Difference between revisions of "Fundamental Interactions"
 
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* [[Fundamental Interactions Group|People and activities]] (← link to current activities and more information on members of the institute with research in Fundamental Interactions, of which the following provides some basic overview)
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Our specializations:
  
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<!-- Our specializations:
   
 
* String theory ([http://hep.itp.tuwien.ac.at/string String Theory Group Webpage])
  
* String theory ([http://hep.itp.tuwien.ac.at/string String Theory Group Webpage])
 
* Strong Interactions, Quark-Gluon-Plasma ([http://hep.itp.tuwien.ac.at/~ipp Ipp], [[Kraemmer]], [[Rebhan]], [[Homepage_Andreas_Schmitt|Schmitt]])
  
* Strong Interactions, Quark-Gluon-Plasma ([http://hep.itp.tuwien.ac.at/~ipp Ipp], [[Kraemmer]], [[Rebhan]], [[Homepage_Andreas_Schmitt|Schmitt]])
 
* Gravitation (Balasin, [http://quark.itp.tuwien.ac.at/~grumil/ Grumiller] - [http://quark.itp.tuwien.ac.at/~grumil/jobs.html START project])
  
* Gravitation (Balasin, [http://quark.itp.tuwien.ac.at/~grumil/ Grumiller] - [http://quark.itp.tuwien.ac.at/~grumil/jobs.html START project])
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* Quantum Field Theory and noncommutative geometry (Schweda)
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* Quantum Field Theory and noncommutative geometry (Schweda) -->
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According to our present knowledge there are four fundamental interactions in nature: gravity, electromagnetism, weak and strong interaction with electromagnetism and weak interaction unified in the electroweak theory. Gravity as well as electromagnetism are macroscopic phenomena, immediately present in our everyday life, like falling objects and static electricity. Weak and strong nuclear interactions, on the other hand, become only important on the microscopic, atomic and subatomic level.
  
According to our present knowledge there are four fundamental interactions in nature: gravity, electromagnetism, weak and strong interaction with electromagnetism and weak interaction unified in the electroweak theory. Gravity as well as electromagnetism are macroscopic phenomena, immediately present in our everyday life, like falling objects and static electricity. Weak and strong nuclear interactions, on the other hand, become only important on the microscopic, atomic and subatomic level.
   
 
The most important aspect of the strong interaction is that it provides stability to the nucleus overcoming electric repulsion, whereas the transmutation of neutrons into protons is the most well-known weak phenomenon. The aim of fundamental physics may be described as obtaining a deeper understanding of these interactions, and penultimately finding a unified framework, which understands the different interactions as different aspects of a single truly fundamental interaction.
  
The most important aspect of the strong interaction is that it provides stability to the nucleus overcoming electric repulsion, whereas the transmutation of neutrons into protons is the most well-known weak phenomenon. The aim of fundamental physics may be described as obtaining a deeper understanding of these interactions, and penultimately finding a unified framework, which understands the different interactions as different aspects of a single truly fundamental interaction.
   
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[[http://quark.itp.tuwien.ac.at/~grumil/pdf/Bachelor_2013.pdf Possible topics for a Bachelor thesis]]
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<!-- [[http://quark.itp.tuwien.ac.at/~grumil/pdf/Bachelor_2013.pdf Possible topics for a Bachelor thesis]] -->
   
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== Research topics ==
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== Quantum field theory ==
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=== Quantum field theory and non-commutative geometry ===
  
   
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Describing the interactions on a more fundamental level the concepts of relativistic quantum field theories are employed. With the advent of quantum mechanics in the first decades of the 20th century it was realized that the electromagnetic field, including light, is quantized and can be seen as a stream of particles, the photons. This implies that the interaction between matter is mediated by the exchange of photons. The concept of relativistic quantum field theory is very simple, unifying a classical field theory with the concepts of quantum theory and special relativity.
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Describing the interactions on a more fundamental level the concepts of relativistic quantum field theories are employed. With the advent of quantum mechanics in the first decades of the 20th century it was realized that the electromagnetic field, including light, is quantized and can be seen as a stream of particles, the photons. This implies that the interaction between matter is mediated by the exchange of photons. In turn, matter particles are excitations of further quantum fields which pervade all of spacetime and which produce incessant vacuum fluctuations.
   
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An example of a pure quantum field theoretical phenomenon is the scattering of light by light, which is impossible in the classical theory of electromagnetism. Quantum fluctuations can turn photons fleetingly into electron-positron pairs which can be exchanged with those of other photons. Light-by-light scattering has only recently been observed directly (in ultrarelativistic heavy-ion collisions at CERN), but it also contributes indirectly to other quantum field theoretical phenomena, in particular to the anomalous magnetic moment of elementary particles. The latter can be measured to such high accuracy that it can be used to test the limits of the present Standard Model of particle physics, because even particles that are much too heavy to be produced in present-day particle colliders make their appearance in vacuum fluctuations.
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[[image:Loop.jpg|Full propagator of free propagation]] <br />
  
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Fig.: Full propagator in terms of free propagation and self-energy corrections.
  
   
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[[image:Lbl.jpg|150px]] &nbsp;&nbsp;&nbsp; [[image:Lblg-2.jpg|200px]] <br />
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The construction of the perturbative NCQFT leads to new types of infrared (IR) singularities which represent a severe obstacle for the renormalization program at higher order and therefore lead to inconsistencies. The IR singularities are produced by the so-called UV finite nonplanar one-loop graphs (which are expected to be UV divergent by naive power counting) in U(N) gauge models and also in scalar field theories. The interplay between expected UV divergencies and the existence of the IR singularities is the so-called UV/IR mixing problem of NCQFT. One also has to stress that the usual UV divergences may be removed by the standard renormalization procedure.
  
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Fig.: Light-by-light scattering (photons respresented by wavy lines, charged particles by lines with arrows), and virtual light-by-light scattering in higher-order corrections to the anomalous magnetic moment of charged particles.
   
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Recent research topics at our institute include hadronic light-by-light scattering where the photon couples to strongly interacting particles. The interactions of the latter are too complex to be captured by perturbation theory and Feynman diagrams, requiring new techniques such as gauge-gravity correspondence. The latter is also known as holography, because it is based on the description of a strongly interacting quantum field theory in flat spacetime as sort of a hologram in a higher-dimensional curved spacetime.
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The present research activities are devoted to find solutions for the UV/IR mixing problem of noncommutative gauge field models. In order to respect the effects of noncommutativity implied by the non-abelian structure a consistent treatment requires the use of the BRS quantization procedure even for a U(1) deformed Maxwell theory.
  
   
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A theoretically clean and well studied example of gauge-gravity duality is the so-called AdS/CFT correspondence, where the higher dimensional spacetime is a maximally symmetric negatively curved (anti de Sitter) space and the quantum field theory in one dimension less is a conformal field theory (CFT). Conformal field theories also play important roles in string theory (see below).
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* Highlight: Our involvement in the [[Myon g-2|muon g-2]] (in German)
 
 
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<!--The construction of the perturbative NCQFT leads to new types of infrared (IR) singularities which represent a severe obstacle for the renormalization program at higher order and therefore lead to inconsistencies. The IR singularities are produced by the so-called UV finite nonplanar one-loop graphs (which are expected to be UV divergent by naive power counting) in U(N) gauge models and also in scalar field theories. The interplay between expected UV divergencies and the existence of the IR singularities is the so-called UV/IR mixing problem of NCQFT. One also has to stress that the usual UV divergences may be removed by the standard renormalization procedure.
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=== Gravitation ===
  
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The present research activities are devoted to find solutions for the UV/IR mixing problem of noncommutative gauge field models. In order to respect the effects of noncommutativity implied by the non-abelian structure a consistent treatment requires the use of the BRS quantization procedure even for a U(1) deformed Maxwell theory.-->
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== Gravitation ==
   
 
Since the groundbreaking work of Einstein, gravitation is conceived as defining the geometry of spacetime - even defining the very concepts of time and space itself. Planetary motion as well as the motion of massless particles, that is to say light, become the straightest possible paths in a non-Euclidean geometry.
  
Since the groundbreaking work of Einstein, gravitation is conceived as defining the geometry of spacetime - even defining the very concepts of time and space itself. Planetary motion as well as the motion of massless particles, that is to say light, become the straightest possible paths in a non-Euclidean geometry.
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=== Quark-Gluon plasma ===
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== Quark-Gluon plasma ==
   
 
Quantum chromodynamics (QCD) is the accepted theory of the strong interactions responsible for the binding of quarks into hadrons such as protons and neutrons, and the binding of protons and neutrons into atomic nuclei. The fundamental particles of QCD, the quarks and gluons, carry a new form of charge, which is called color because of its triplet nature in the case of the quarks (e.g. red, green, blue); gluons come in eight different colors which are composites of color and anticolor charges. However, quarks and gluons have never been observed as free particles. Nevertheless, because quarks have also electrical charge, they can literally be seen as constituents of hadrons by deep inelastic scattering using virtual photons. The higher the energy of the probing photon, the more do the quarks appear as particles propagating freely within a hadron. This feature is called "asymptotic freedom". It arises from so-called nonabelian gauge field dynamics, with gluons being the excitations of the nonabelian gauge fields similarly to photons being the excitations of the electromagnetic fields, except that gluons also carry color charges. Asymptotic freedom is well understood, and the Nobel prize was awarded to its main discoverers Gross, Politzer, and Wilczek in 2004.
  
Quantum chromodynamics (QCD) is the accepted theory of the strong interactions responsible for the binding of quarks into hadrons such as protons and neutrons, and the binding of protons and neutrons into atomic nuclei. The fundamental particles of QCD, the quarks and gluons, carry a new form of charge, which is called color because of its triplet nature in the case of the quarks (e.g. red, green, blue); gluons come in eight different colors which are composites of color and anticolor charges. However, quarks and gluons have never been observed as free particles. Nevertheless, because quarks have also electrical charge, they can literally be seen as constituents of hadrons by deep inelastic scattering using virtual photons. The higher the energy of the probing photon, the more do the quarks appear as particles propagating freely within a hadron. This feature is called "asymptotic freedom". It arises from so-called nonabelian gauge field dynamics, with gluons being the excitations of the nonabelian gauge fields similarly to photons being the excitations of the electromagnetic fields, except that gluons also carry color charges. Asymptotic freedom is well understood, and the Nobel prize was awarded to its main discoverers Gross, Politzer, and Wilczek in 2004.
   
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Much less understood is the phenomenon of "confinement", which means that only color-neutral bound states of quarks and gluons exist. This confinement can in fact be broken in a medium if the density exceeds significantly that of nuclear matter. When hadrons overlap so strongly that they loose their individuality, quarks and gluons come into their own as the elementary degrees of freedom. It is conceivable that such conditions are realized in the cores of certain neutron stars.
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Much less understood is the phenomenon of "confinement", which means that only color-neutral bound states of quarks and gluons can be observed. This confinement can be overcome when the temperature is very large, as, for example, in the first instances of the Early Universe. In this case, quarks and gluons form a quantum fluid that is known as the quark-gluon plasma. Its unique properties are studied on Earth in large collider facilities at LHC (CERN, Switzerland) or at RHIC (BNL, United States), where this plasma is created in ultrarelativistic heavy-ion collision experiments.
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<!--Much less understood is the phenomenon of "confinement", which means that only color-neutral bound states of quarks and gluons exist. This confinement can in fact be broken in a medium if the density exceeds significantly that of nuclear matter. When hadrons overlap so strongly that they loose their individuality, quarks and gluons come into their own as the elementary degrees of freedom. It is conceivable that such conditions are realized in the cores of certain neutron stars.-->
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[[Image:Phase_diag03.jpg|phase diagram of quark-gluon matter]] <br />
  
[[Image:Phase_diag03.jpg|phase diagram of quark-gluon matter]] <br />
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Fig.: Qualitative sketch of the phase diagram of quark-gluon matter as a function of temperature T and quark chemical potential µ. Solid lines denote rst-order phase transitions, the dashed line a rapid crossover.
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Fig.: Qualitative sketch of the expected phase diagram of quark-gluon matter as a function of temperature T and quark chemical potential µ. Solid lines denote first-order phase transitions, the dashed line a rapid crossover.
   
   
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In our group, we investigate different thermal and nonthermal properties of the quark-gluon plasma, putting particular emphasis on its non-equilibrium early-time evolution shortly after the heavy-ion collision. Using a variety of different techniques, involving perturbative calculations, kinetic theory, hydrodynamics, holography, real-time lattice simulations and artificial neural networks, not only enables us to extract dynamical and universal key features of the plasma, but also to link to other fields of research like machine learning, gravity, the Early Universe and experiments with ultra-cold Bose gases.
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At comparatively low temperatures, quark matter is known to form Cooper pairs and turns into a color superconductor. Also at temperatures just above the superconductivity phase new phenomena appear, which reflect that quark matter has strong deviations from an ideal Fermi liquid. In particular, there is anomalous behaviour in the low-temperature specific heat, which has been calculated for the first time systematically by our group. This has already found application in revised calculations of the cooling behavior of young neutron stars.
  
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<!--At comparatively low temperatures, quark matter is known to form Cooper pairs and turns into a color superconductor. Also at temperatures just above the superconductivity phase new phenomena appear, which reflect that quark matter has strong deviations from an ideal Fermi liquid. In particular, there is anomalous behaviour in the low-temperature specific heat, which has been calculated for the first time systematically by our group. This has already found application in revised calculations of the cooling behavior of young neutron stars.-->
   
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=== String theory ===
  
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== String theory ==
   
 
The names of the fundamental forces are related to their strength. The strong force is much stronger than electromagnetism and is thus able to overcome the repulsive force between objects with the same electrical charge (protons or quarks). The weak force is weaker than electromagnetism but still much stronger than gravity. The reason that we almost only recognize gravity in everyday life is that the macroscopic objects are neutral. They don't carry an effective color charge and they carry - if at all - only very small electric charges. For gravity there is no negative charge (negative mass), so that all the small gravitational effects add up to something which is strong enough to move galaxies and build black holes. The seperate description of the forces is quite accurate by now. This is summarized in the standard model of particle physics.
  
The names of the fundamental forces are related to their strength. The strong force is much stronger than electromagnetism and is thus able to overcome the repulsive force between objects with the same electrical charge (protons or quarks). The weak force is weaker than electromagnetism but still much stronger than gravity. The reason that we almost only recognize gravity in everyday life is that the macroscopic objects are neutral. They don't carry an effective color charge and they carry - if at all - only very small electric charges. For gravity there is no negative charge (negative mass), so that all the small gravitational effects add up to something which is strong enough to move galaxies and build black holes. The seperate description of the forces is quite accurate by now. This is summarized in the standard model of particle physics.
   
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There is only one particle (the Higgs boson), which is predicted by the standard model and has not yet been found. A measure for the strength of a force are the coupling constants of the corresponding theory. They are, however, not constant, but depend on the energy level one is dealing with. If one extrapolates their values to high energies, one discovers that the couplings of electromagnetism, strong and weak force meet at a certain energy level almost in one single point (see Figure 1). This supports the idea that those three forces could be just different aspects of one and the same universal force. There are several theories which try to describe this unification. They are called GUTs, 'grand unified theories'. However, to be really 'grand', such a unification should also include gravity, whose coupling constant is far weaker still at this high energies. The theory, which will manage to unify all forces, including gravity, is sometimes called TOE, "theory of everything". String theory is one candidate, and at present actually the only one for this TOE.
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A measure for the strength of a force are the coupling constants of the corresponding theory. They are, however, not constant, but depend on the energy level one is dealing with. If one extrapolates their values to high energies, one discovers that the couplings of electromagnetism, strong and weak force meet at a certain energy level almost in one single point (see Figure 1). This supports the idea that those three forces could be just different aspects of one and the same universal force. There are several theories which try to describe this unification. They are called GUTs, 'grand unified theories'. However, to be really 'grand', such a unification should also include gravity, whose coupling constant is far weaker still at this high energies. The theory, which will manage to unify all forces, including gravity, is sometimes called TOE, "theory of everything". String theory is one candidate, and at present actually the only one for this TOE.
   
 
[[Image:Particle_string_interaction.jpg| Point particle and closed string interaction]] <br />
  
[[Image:Particle_string_interaction.jpg| Point particle and closed string interaction]] <br />
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'SUSY' stands for supersymmetry and means that there is an exchange symmetry between fermionic particles (like quarks and electrons) and bosonic ones (like photons and even gravitons, if one includes gravity into the considerations). It does, however, not relate the already known particles, but it predicts new supersymmetric partners to the known particles (called e.g. squarks, selectrons, photinos and gravitinos). So far none of those superparticles has been discovered, but there are a lot of theoretical reasons for believing in supersymmetry. Supersymmetry is an integral part of string theory, or more precisely 'superstring theory'. Within one year now, the new accelerator LHC (large hadron collider) at CERN will start and try to produce the Higgs boson and the superparticles mentioned above and will therefore also be a first test for string theory.
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'SUSY' stands for supersymmetry and means that there is an exchange symmetry between fermionic particles (like quarks and electrons) and bosonic ones (like photons and even gravitons, if one includes gravity into the considerations). It does, however, not relate the already known particles, but it predicts new supersymmetric partners to the known particles (called e.g. squarks, selectrons, photinos and gravitinos). So far none of those superparticles has been discovered, but there are a lot of theoretical reasons for believing in supersymmetry. Supersymmetry is an integral part of string theory, or more precisely 'superstring theory'. If supersymmetry is realized at energies not too far above the scale of electroweak symmetry breaking, the Large Hadron Collider at CERN may be able to discover its signatures in its ongoing searches of physics beyond the standard model.
   
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For further information and news on fundamental physics visit:
  
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== Further Information ==
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This contains the public outreach web pages of the [http://www.teilchen.at Fachausschuss f&uuml;r Kern- und Teilchenphysik (FAKT)] of the [http://www.oepg.at/ &Ouml;PG] (Austrian Physical Society), which our institute are hosting.
  
   
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* [https://owncloud.tuwien.ac.at/index.php/s/1kJ4NNZ6xJOz6q3 Presentation slides] for the course 138.039 - Introduction into the Fields of Science and Research of the Faculty of Physics
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* [[Fundamental_Interactions_Preprints|(Some of) our preprints in the field of fundamental interactions]] (Complete lists of preprints and publications can now be found https://arxiv.org and https://inspirehep.net by searching by author)
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== Preprints ==
  
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Preprints of the group '''Fundamental Interactions''':
  
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=== Current year ===
  
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* <b>TUW-14-01</b> M. Gary, D. Grumiller, S. Prohazka, and S.-J. Rey, ''Lifshitz Holography with Isotropic Scale Invariance '' [http://arxiv.org/abs/1406.1468 hep-th/1406.1468]
  
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* <b>TUW-14-02</b> S. Detournay, D. Grumiller, F. Schöller and J. Simon, ''Variational principle and 1-point functions in 3-dimensional flat space Einstein gravity '' [http://arxiv.org/abs/1402.3687 hep-th/1402.3687]
  
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* <b>TUW-14-03</b> D. Grumiller, R. McNees and J. Salzer, ''Black holes and thermodynamics - The first half century'' [http://arxiv.org/abs/1402.5127 hep-th/1402.5127]
  
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* <b>TUW-14-04</b> H. Afshar, T. Creutzig, D. Grumiller, Y. Hikida and P. Ronne, ''Unitary W-algebras and three-dimensional higher spin gravities with spin one symmetry'' [http://arxiv.org/abs/1404.0010 1404.0010]
  
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* <b>TUW-14-05</b> D. Grumiller, M. Riegler and J. Rosseel, ''Unitarity in three-dimensional flat space higher spin theories'' [http://arxiv.org/abs/1403.5297 hep-th/1403.5297]
  
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* <b>TUW-14-06</b> V. Keranen, H Nishimura, S. Stricker, O. Taanila, A. Vuorinen, ''Universality in holographic entropy production'' [http://arxiv.org/abs/arXiv:1405.7015 1405.7015]
  
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* <b>TUW-14-07</b> A. Bagchi, S. Detournay, D. Grumiller, S. Prohazka and M. Riegler, ''Holographic Chern-Simons Theories'' [http://arxiv.org/abs/1404.1919 1404.1919]
  
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* <b>TUW-14-08</b> D. Grumiller, R. McNees and J. Salzer, ''Cosmological constant as confining U(1) charge in two-dimensional dilaton gravity'' [http://arxiv.org/abs/1406.7007 1406.7007]
  
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* <b>TUW-14-09</b> Harald Skarke, ''The Evolution of an Inhomogeneous Universe'' [http://arxiv.org/abs/1407.6602 1407.6602]
  
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* <b>TUW-14-10</b> A. Bagchi, D. Grumiller, J. Salzer, S. Sarkar and F. Schöller, ''Flat space cosmologies in two dimensions'' [http://arxiv.org/abs/1408.5337 1408.5337]
 
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* <b>TUW-14-11</b> P. Anastasopoulos and R. Richter, ''Light stringy state production'' [http://arxiv.org/abs/1408.4810 1408.4810]
  
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* <b>TUW-14-12</b> M. Riegler, ''Flat space limit of Cardy formula'' [http://arxiv.org/abs/1408.6931 1408.6831]
  
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* <b>TUW-14-13</b> R. Baier, H. Nishimura, S. Stricker, ''Scalar field collapse with negative cosmological constant'' [http://arxiv.org/abs/1410.3495 1410.3495]
  
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* <b>TUW-14-14</b> A. Bagchi, R. Basu, D. Grumiller, M. Riegler, ''Entanglement entropy in Galilean conformal field theories and flat holography'' [http://arxiv.org/abs/arXiv:1410.4089 1410.4089]
  
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* <b>TUW-14-15</b> M. Gary, D. Grumiller, M. Riegler and J. Rosseel, ''Flat space (higher spin) gravity with chemical potentials'' [http://arxiv.org/abs/arXiv:1411.3728 1411.3728]
 
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=== 2013 ===
  
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* <b>TUW-13-01</b> D. Grumiller, W. Riedler, J. Rosseel and T. Zojer, ''Holographic applications of logarithmic conformal field theories'' [http://arxiv.org/abs/1302.0280 hep-th/1302.0280]
  
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* <b>TUW-13-02</b> M. Attems, A. Rebhan, M. Strickland, ''Longitudinal thermalization via the chromo-Weibel instability'' [http://arxiv.org/abs/1301.7749 hep-ph/1301.7749]
  
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* <b>TUW-13-03</b> M. Attems, A. Rebhan, M. Strickland, ''The chromo-Weibel instability in an expanding background'' [http://arxiv.org/abs/1302.5098 hep-ph/1302.5098]
  
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* <b>TUW-13-04</b> Roberto Emparan, Daniel Grumiller and Kentaro Tanabe, ''Large D gravity and low D strings'' [http://arxiv.org/abs/arXiv:1303.1995 hep-th/1303.1995]
  
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*<b>TUW-13-05</b> Steineder, Stricker, Vuorinen, ''Probing the pattern of holographic thermalization with photons'' [http://arxiv.org/abs/arXiv:1304.3404 hep-ph/1304.3404]
  
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*<b>TUW-13-06</b> Arjun Bagchi, Stephane Detournay and Daniel Grumiller, Joan Simon, ''Cosmic evolution from phase transition of 3-dimensional flat space'' [http://arxiv.org/abs/arXiv:1305.2919 hep-th/1305.2919]
  
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*<b>TUW-13-07</b> R. Andringa, E. Bergshoeff, J. Rosseel and E. Sezgin, ''Newton-Cartan Supergravity'' [http://arxiv.org/abs/arXiv:1305.6737 hep-th/1305.6737]
  
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*<b>TUW-13-08</b> S. Stricker, ''Holographic thermalization in N=4 Super Yang-Mills theory at finite coupling'' [http://arxiv.org/abs/arXiv:1307.2736 hep-th/1307.2736]
  
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*<b>TUW-13-09</b> H. Afshar, A. Bagchi, R. Fareghbal, D. Grumiller and J. Rosseel, ''Higher spin theory in 3-dimensional flat space,'' [http://arXiv.org/abs/1307.4768 hep-th/1307.4768]
  
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*<b>TUW-13-10</b> H. R. Afshar, ''Flat/AdS boundary conditions in three dimensional conformal gravity,'' [http://www.arXiv.org/abs/1307.4855 hep-th/1307.4855]
  
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*<b>TUW-13-11</b> M. Gary, ''Still No Rindler Firewalls,'' [http://www.arXiv.org/abs/1307.4972 hep-th/1307.4972]
  
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*<b>TUW-13-12</b> K. Hori and J. Knapp, ''Linear Sigma Models With Strongly Coupled Phases - One Parameter Models,'' [http://www.arXiv.org/ hep-th/1308.xxxx]
  
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*<b>TUW-13-13</b> R. Baier, S. Stricker, O. Taanila, ''Critical scalar field collpase in AdS3: an analytic approach,'' [http://www.arXiv.org/ hep-th/1309.xxxx]
  
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*<b>TUW-13-14</b> D. Parganlija, P. Kovacs, Gy. Wolf, F. Giacosa and D. Rischke, ''Eta, Eta' and eLSM'', [http://arxiv.org/abs/arXiv:1301.3478 hep-ph/1301.3478]
  
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*<b>TUW-13-15</b> D. Grumiller, M. Irakleidou, I. Lovrekovic and R. McNees, ''Conformal gravity holography in four dimensions'', [http://arxiv.org/abs/arXiv:1310.0819 hep-th/1310.0819]
  
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*<b>TUW-13-16</b> Harald Skarke, ''Inhomogeneity implies Accelerated Expansion'', [http://arxiv.org/abs/arXiv:1310.1028 astro-ph.CO/1310.1028]
  
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*<b>TUW-13-17</b> D. Arnaudov, R.C. Rashkov and T. Vetsov, ''On the algebraic curves for circular and folded strings in AdS5 x S5,'' [http://www.arXiv.org/abs/1311.6114 hep-th/1311.6114]
  
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*<b>TUW-13-18</b> Daniel Grumiller, Mauricio Leston and Dmitri Vassilevich, ''Anti-de Sitter holography for gravity and higher spin theories in two dimensions'', [http://arxiv.org/abs/arXiv:1311.7413 hep-th/1311.7413]
  
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=== 2012 ===
  
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* <b>TUW-12-01</b> M. Gary, D. Grumiller and R. Rashkov, ''Towards non-AdS holography in 3-dimensional higher spin gravity'' [http://www.arXiv.org/abs/1201.0013 hep-th/1201.0013]
  
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* <b>TUW-12-02</b> P. Anastasopoulos, I. Antoniadis, K. Benakli, M.D.Goodsel and A. Vichi, ''One-loop adjoint masses for branes at non-supersymmetric angles'' [http://arxiv.org/abs/1201.2663 hep-th/1201.2663]
  
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* <b>TUW-12-03</b> A. Ipp, J. Evers, C. H. Keitel, K. Z. Hatsagortsyan, ''Streaking at high energies with electrons and positrons'' [http://arxiv.org/abs/1202.0180 hep-ph/1202.0180]
  
−  
−
* <b>TUW-12-04</b> A.P. Braun, A. Collinucci and R. Valandro, ''Algebraic description of G-flux in F-theory: new techniques for F-theory phenomenology'' [http://arxiv.org/abs/1202.5029 hep-th/1202.5029]
  
−  
−
* <b>TUW-12-05</b> H. Steinacker, ''Gravity and compactified branes in matrix models'' [http://arxiv.org/abs/1202.6306 hep-th/1202.6306]
  
−  
−
* <b>TUW-12-06</b> Gabriela-Raluca Mocanu and Daniel Grumiller ''Self-organized criticality in boson clouds around black holes'' [http://arxiv.org/abs/1203.4681 astro-ph/1203.4681]
  
−  
−
* <b>TUW-12-07</b> Victor Batyrev and Maximilian Kreuzer ''Conifold degenerations of Fano 3-folds as hypersurfaces in toric varieties'' [http://arxiv.org/abs/1203.6058 math.AG/1203.6058]
  
−  
−
* <b>TUW-12-08</b> Harald Skarke ''How to Classify Reflexive Gorenstein Cones'' [http://arxiv.org/abs/1204.1181 hep-th/1204.1181]
  
−  
−
* <b>TUW-12-09</b> Niklas Johansson, Ali Naseh and Thomas Zojer ''Holographic two-point functions for 4d log-gravity'' [http://arxiv.org/abs/1205.5804 hep-th/1205.5804]
  
−  
−
* <b>TUW-12-10</b> A.P. Braun, J.Knapp, E.Scheidegger, H.Skarke and N.-O. Walliser ''PALP: a User Manual'' [http://arxiv.org/abs/1205.4147 math.AG/1205.4147]
  
−  
−
* <b>TUW-12-11</b> D.Arnaudov, R.C.Rashkov ''On semiclassical four-point correlators in AdS5 x S5'' [http://arxiv.org/abs/1206.2613 hep-th/1206.2613]
  
−  
−
* <b>TUW-12-12</b> A. Ipp, P. Somkuti ''Yoctosecond metrology through HBT correlations from a quark-gluon plasma'' [http://arxiv.org/abs/1207.0197 hep-th/1207.0197]
  
−  
−
* <b>TUW-12-13</b> R. Baier, S. Stricker, O. Taanila, A. Vuorinen ''Production of Prompt Photons: Holographic Duality and Thermalization'' [http://arxiv.org/abs/arXiv:1207.1116 hep-ph/1207.1116]
  
−  
−
* <b>TUW-12-14</b> R. Baier, S. Stricker, O. Taanila, A. Vuorinen ''Holographic dilepton production in a thermalizing plasma'' [http://arxiv.org/abs/arXiv:1205.2998 hep-ph/1205.2998]
  
−  
−
* <b>TUW-12-15</b> A. Rebhan, D. Steineder ''Probing Two Holographic Models of Strongly Coupled Anisotropic Plasma'' [http://arxiv.org/abs/arXiv:1205.4684 hep-th/1205.4684]
  
−  
−
* <b>TUW-12-16</b> M. Attems, A. Rebhan, M. Strickland ''Instabilities of an anisotropically expanding non-Abelian plasma: 3D+3V discretized hard-loop simulations'' [http://arxiv.org/abs/arXiv:1207.5795 hep-ph/1207.5795]
  
−  
−
* <b>TUW-12-17</b> P. Candelas, A. Constantin, H. Skarke ''An Abundance of K3 Fibrations from Polyhedra with Interchangeable Parts'' [http://arxiv.org/abs/1207.4792 hep-th/1207.4792]
  
−  
−
* <b>TUW-12-18</b> A. Gynther, A. Rebhan, D. Steineder ''Thermodynamics and phase diagram of anisotropic Chern-Simons deformed gauge theories'' [http://arxiv.org/abs/arXiv:1207.6283 hep-th/1207.6283]
  
−  
−
* <b>TUW-12-19</b> Michal Michalcik, Radoslav C. Rashkov, "On finite size corrections to the dispersion relations of giant magnon and single spike on γ-deformed T^{1,1}" [http://arxiv.org/abs/arXiv:1208.0698 hep-th/1208.0698]
  
−  
−
* <b>TUW-12-20</b> Arjun Bagchi, Stephane Detournay and Daniel Grumiller ''Flat-Space Chiral Gravity'' [http://arxiv.org/abs/arXiv:1208.1658 hep-th/1208.1658]
  
−  
−
* <b>TUW-12-21</b> Stanley Deser, Sabine Ertl and Daniel Grumiller ''Canonical bifurcation in higher derivative, higher spin, theories'' [http://arxiv.org/abs/arXiv:1208.0339 hep-th/1208.0339]
  
−  
−
* <b>TUW-12-22</b> H. Afshar, M. Gary, D. Grumiller, R. Rashkov and M. Riegler ''Non-AdS holography in 3-dimensional higher spin gravity - General recipe and example'' [http://arxiv.org/abs/arXiv:1209.2860 hep-th/1209.2860]
  
−  
−
* <b>TUW-12-23</b> D. Steineder, S. A. Stricker and A. Vuorinen ''Thermalization at intermediate coupling'' [http://arxiv.org/abs/arXiv:1209.0291 hep-ph/1209.0291]
  
−  
−
* <b>TUW-12-24</b> M. Gary ''A Holographic Holographic Bound and the Black Hole S-Matrix'' [http://arxiv.org/abs/arXiv:1209.3040 hep-th/1209.3040]
  
−  
−
* <b>TUW-12-25</b> M. Bertin, S. Ertl, P. Ghorbani, D. Grumiller, N. Johansson and D. Vassilevich ''Lobachevsky holography in conformal Chern-Simons gravity'' [http://arxiv.org/abs/arXiv:1212.3335 hep-th/1212.3335]
  
−  
−
* <b>TUW-12-26</b> J. Aparicio, D. Grumiller, E. Lopez, I. Papadimitriou and S. Stricker ''Bootstrapping gravity solutions'' [http://arxiv.org/abs/arXiv:1212.3609 hep-th/1212.3609]
  
−  
−
* <b>TUW-12-27</b> Harald Skarke ''Why is the Legendre Transformation Involutive?'' [http://arxiv.org/abs/arXiv:1209.6193 math-ph/1209.6193]
  
−  
−
* <b>TUW-12-28</b> K. Chelabi, M. Schweda and S. Kouadik ''Translation-Invariant Renormalizable Noncommutative Chern-Simons Theory'' [http://arxiv.org/abs/arXiv:1207.4591 hep-th/1207.4591]
  
−  
−
* <b>TUW-12-29</b> D. N. Blaschke, T. Garschall, F. Gieres, F. Heindl, M. Schweda and M. Wohlgenannt ''On the Renormalization of Non-Commutative Field Theories'' [http://arxiv.org/abs/arXiv:1207.5494 hep-th/1207.5494]
  
−  
−
* <b>TUW-12-30</b> D. Grumiller, R. McNees and S. Zonetti, ''Black holes in the conical ensemble'', [http://arxiv.org/abs/arXiv:1210.6904 gr-qc/1210.6904]
  
−  
−
* <b>TUW-12-31</b> A. Ipp, ''Unstable dynamics of Yang-Mills fields at early times of heavy ion collisions'', [http://arxiv.org/abs/arXiv:1210.5150 hep-th/1210.5150]
  
−  
−
* <b>TUW-12-32</b> P. Anastasopoulos, M. Cvetic, R. Richter, P. Vaudrevange ''Discrete symmetries in semi-realistic orientifold compactifications'', [http://arxiv.org/abs/arXiv:1210.xxxx hep-th/1210.xxxx]
  
−  
−
* <b>TUW-12-33</b> P. Anastasopoulos, M. Goodsell, R. Richter, ''Excited twist correlators in open string models'', [http://arxiv.org/abs/arXiv:1211.xxxx hep-th/1211.xxxx]
  
−  
−
* <b>TUW-12-34</b> H. Afshar, M. Gary, D. Grumiller, R. Rashkov and M. Riegler, ''Semi-classical unitarity in 3-dimensional higher-spin gravity for non-principal embeddings'', [http://arxiv.org/abs/arXiv:1211.4454 hep-th/1211.4454]
  
−  
−
* <b>TUW-12-35</b> H. Afshar, H. Firouzjahi and S. Parvizi, ''dS solutions with co-dimension two branes in six dimensions'', [http://arxiv.org/abs/arXiv:1212.xxxx hep-th/1212.xxxx]
  
−  
−
* <b>TUW-12-36</b> D. Parganlija, ''Quarkonium Phenomenology in Vacuum'', [http://arxiv.org/abs/arXiv:1208.0204 hep-ph/1208.0204]
  
−  
−
* <b>TUW-12-37</b> D. Parganlija, P. Kovacs, Gy. Wolf, F. Giacosa and D. Rischke, ''Meson vacuum phenomenology in a three-flavor linear sigma model with (axial-)vector mesons'', [http://arxiv.org/abs/arXiv:1208.0585 hep-ph/1208.0585]
  
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−
* <b>TUW-12-38</b> D. Parganlija, P. Kovacs, Gy. Wolf, F. Giacosa and D. Rischke, ''Phenomenology of Axial-Vector Mesons from an Extended Linear Sigma Model'', [http://arxiv.org/abs/arXiv:1208.2054 hep-ph/1208.2054]
  
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−
* <b>TUW-12-39</b> D. Parganlija, P. Kovacs, Gy. Wolf, F. Giacosa and D. Rischke, ''Scalar mesons in a linear sigma model with (axial-)vector mesons'', [http://arxiv.org/abs/arXiv:1208.5611 hep-ph/1208.5611]
  
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−
* <b>TUW-12-40</b> F. Giacosa, D. Parganlija, P. Kovacs and Gy. Wolf, ''Phenomenology of light mesons within a chiral approach'', [http://arxiv.org/abs/arXiv:1208.6202 hep-ph/1208.6202]
  
−  
−
* <b>TUW-12-41</b> D. Parganlija, ''Scalar Mesons and FAIR'', [http://arxiv.org/abs/arXiv:1211.4804 hep-ph/1211.4804]
  
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=== 2011 ===
  
−  
−
* <b>TUW-11-01</b> R. S. Garavuso, L. Katzarkov, M. Kreuzer and A. Noll, ''Super Landau-Ginzburg mirrors and algebraic cycles'' [http://arxiv.org/abs/1101.1368 hep-th/1101.1368]
  
−  
−
* <b>TUW-11-02</b> J. Knapp, M. Kreuzer, C. Mayrhofer and N.-O. Walliser, ''Toric Construction of Global F-Theory GUTs'', JHEP03(2011)138, [http://arxiv.org/abs/1101.4908 hep-th/1101.4908]
  
−  
−
* <b>TUW-11-03</b> J. Knapp and M. Kreuzer, ''Toric Methods in F-theory Model Building'' [http://arxiv.org/abs/1103.3358 hep-th/1103.3358]
  
−  
−
* <b>TUW-11-04</b> A. Ipp, ''Yoctosecond photon pulse generation in heavy ion collisions'' [http://arxiv.org/abs/1102.0420 hep-ph/1102.0420]
  
−  
−
* <b>TUW-11-05</b> S. Carloni, D. Grumiller and F. Preis, ''Solar system constraints on Rindler acceleration'' [http://arxiv.org/abs/1103.0274 astro-ph/1103.0274]
  
−  
−
* <b>TUW-11-06</b> M. Bertin, D. Grumiller, D. Vassilevich and T. Zojer, ''Generalised massive gravity one-loop partition function and AdS/(L)CFT'' [http://arxiv.org/abs/1103.5468 hep-th/1103.5468]
  
−  
−
* <b>TUW-11-07</b> H. Afshar, B. Cvetkovic, S. Ertl, D. Grumiller and N. Johansson, ''Holograms of Conformal Chern-Simons Gravity'' [http://arxiv.org/abs/1106.6299 hep-th/1106.6299]
  
−  
−
* <b>TUW-11-08</b> D. Arnaudov, R.C. Rashkov, and T. Vetsov, ''Three- and four-point correlators of operators dual to folded string solutions in AdS_5 x S^5'' [http://arxiv.org.abs/1103.6145 hep-th/1103.6145]
  
−  
−
* <b>TUW-11-09</b> P. Anastasopoulos, I. Antoniadis, K. Benakli, M.D.Goodsel and A. Vichi, ''One-loop adjoint masses for non-supersymmetric intersecting branes'' [http://arxiv.org.abs/1105.0591 hep-th/1105.0591]
  
−  
−
* <b>TUW-11-10</b> D. Arnaudov and R.C. Rashkov, ''Quadratic corrections to three-point functions'' [http://arxiv.org.abs/1106.0859 hep-th/1106.0859]
  
−  
−
* <b>TUW-11-11</b> D. Arnaudov and R.C. Rashkov, ''Three-point correlators: examples from Lunin-Maldacena background'' [http://arxiv.org.abs/1106.4298 hep-th/1106.4298]
  
−  
−
* <b>TUW-11-12</b> A. P. Braun and N.-O. Walliser, ''A new offspring of PALP'' [http://arxiv.org.abs/1106.4529 hep-th/1106.4529]
  
−  
−
* <b>TUW-11-13</b> A. Rebhan and D. Steineder, ''Electromagnetic signatures of a strongly coupled anisotropic plasma'' [http://arxiv.org/abs/1106.3539 hep-th/1106.3539]
  
−  
−
* <b>TUW-11-14</b> M. Cicoli, M. Kreuzer and Christoph Mayrhofer, ''Toric K3-Fibred Calabi-Yau Manifolds with del Pezzo Divisors for String Compactifications'' [http://arxiv.org/abs/1107.0383 hep-th/1107.0383]
  
−  
−
* <b>TUW-11-15</b> D. Grumiller and F. Preis, ''Rindler force at large distances'' [http://arxiv.org/abs/1107.2373 astro-ph/1107.2373]
  
−  
−
* <b>TUW-11-16</b> C.-M. Chen, S. Hu, T. Li, D.V. Nanopoulos, ''Type IIB Supersymmetric Flux vacua'' [http://arxiv.org/abs/1107.3465 hep-th/1107.3465]
  
−  
−
* <b>TUW-11-17</b> K. Z. Hatsagortsyan, A. Ipp, J. Evers, A. Di Piazza, and C. H. Keitel, ''Ultra-strong laser pulses: streak-camera for gamma-rays via pair production and quantum radiative reaction'' [http://arxiv.org/abs/1107.4036 physics.ins-det/1107.4036]
  
−  
−
* <b>TUW-11-18</b> D. Burke and R. Wimmer, ''Quantum energies and tensorial central charges of confined monopoles'' [http://arxiv.org/abs/1107.3568 hep-th/1107.3568]
  
−  
−
* <b>TUW-11-19</b> A.P. Braun, A. Collinucci and R. Valandro, ''G-Flux in F-theory and algebraic cycles'' [http://arxiv.org/abs/1107.5337 hep-th/1107.5337]
  
−  
−
* <b>TUW-11-20</b> A.P. Braun, N. Johansson, M. Larfors and N.-O. Walliser, ''Restrictions on infinite sequences of type IIB vacua'' [http://arxiv.org/abs/1108.1394 hep-th/1108.1394]
  
−  
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* <b>TUW-11-21</b> S. Carlip and D. Grumiller, ''Lower bound on the spectral dimension near a black hole'' [http://arxiv.org/abs/1108.4686 gr-qc/1108.4686]
  
−  
−
* <b>TUW-11-22</b> H. Afshar, B. Cvetkovic, S. Ertl, D. Grumiller and N. Johansson, ''Conformal Chern-Simons holography - lock, stock and barrel'' [http://arxiv.org/abs/1110.5644 hep-th/1110.5644]
  
−  
−
* <b>TUW-11-23</b> P. Anastasopoulos, M. Bianchi and R. Richter, ''Light stringy states'' [http://arxiv.org/abs/1110.5424 hep-th/1110.5424]
  
−  
−
* <b>TUW-11-24</b> P. Anastasopoulos, M. Bianchi and R. Richter, ''On closed-string twist-field correlators and their open-string descendants'' [http://arxiv.org/abs/1110.5359 hep-th/1110.5359]
  
−  
−
* <b>TUW-11-25</b> Michal Michalcik, Radoslav C. Rashkov, Maria Schimpf, ''Three-point correlators: Examples from Lunin-Maldacena background '' [http://arxiv.org.abs/1107.5795 hep-th/1107.5795]
  
−  
−
* <b>TUW-11-26</b> D. Arnaudov and R.C. Rashkov, ''Subleading semiclassical four-poinr functions'' [http://arxiv.org.abs/1111.xxxx hep-th/1111.xxxx]
  
−  
−
* <b>TUW-11-27</b> F. Preis, A. Rebhan and A. Schmitt, ''Holographic baryonic matter in a background magnetic field'' [http://arxiv.org/abs/1109.6904 hep-th/1109.6904]
  
−  
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* <b>TUW-11-28</b> A. Rebhan and D. Steineder, ''Violation of the Holographic Viscosity Bound in a Strongly Coupled Anisotropic Plasma'' [http://arxiv.org/abs/1110.6825 hep-th/1110.6825]
  
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=== 2010 ===
  
−  
−
* <b>TUW-10-01</b> D.N. Blaschke, E. Kronberger, R.I.P. Sedmik and M. Wohlgenannt, ''Gauge Theories on Deformed Spaces'' [http://arxiv.org/abs/1106.4529 math.AG/1106.4529]
  
−  
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* <b>TUW-10-02</b> V.G. Filev and R.C. Rashkov, ''Magnetic Catalysis of Chiral Symmetry Breaking. A Holographic Prospective.'' [http://arxiv.org/abs/1010.0444 hep-th/1010.0444]
  
−  
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* <b>TUW-10-03</b> S. Ertl, D. Grumiller and N. Johansson, All stationary axi-symmetric local solutions of topologically massive gravity. [http://arxiv.org/abs/1006.3309 hep-th/1006.3309]
  
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* <b>TUW-10-04</b> A. Gynther, K. Landsteiner, F. Pena-Benitez and A. Rebhan, ''Holographic Anomalous Conductivities and the Chiral Magnetic Effect'' [http://arxiv.org/abs/1005.2587 hep-th/1005.2587]
  
−  
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* <b>TUW-10-05</b> C. P. Herzog, S. A. Stricker and A. Vuorinen, ''Hyperfine splitting and the Zeeman effect in holographic heavy-light mesons'' [http://arxiv.org/abs/1005.3285 hep-th/1005.3285]
  
−  
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* <b>TUW-10-06</b> C.-M. Chen and Y.-C. Chung, ''Flipped SU(5) GUTs from E8 singularity in F-theory'' [http://arxiv.org/abs/1005.5728 hep-th/1005.5728]
  
−  
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* <b>TUW-10-07</b> C.-M. Chen , J. Knapp , M. Kreuzer and C. Mayrhofer, ''Global SO(10) F-theory GUTs'' [http://arxiv.org/abs/1005.5735 hep-th/1005.5735]
  
−  
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* <b>TUW-10-08</b> M. Schweda and M. Wohlgenannt, ''On NCQFT and dimensionless insertions'' [http://arxiv.org/abs/1005.5107 hep-th/1005.5107]
  
−  
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* <b>TUW-10-09</b> D. Arnaudov, H. Dimov and R.C. Rashkov, ''On the pulsating strings in $AdS_5\times T^{1,1}$ '' [http://arxiv.org/abs/1005.5334 hep-th/1005.1539]
  
−  
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* <b>TUW-10-10</b> Jean-Paul Blaizot, Andreas Ipp, Nicolás Wschebor, ''Calculation of the pressure of a hot scalar theory within the Non-Perturbative Renormalization Group'' [http://arxiv.org/abs/1007.0991 hep-th/1007.0991]
  
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* <b>TUW-10-11</b> Matthias R. Gaberdiel, Daniel Grumiller and Dmitri Vassilevich, ''Graviton 1-loop partition function for 3-dimensional massive gravity'' [http://arxiv.org/abs/1007.5189 hep-th/1007.5189]
  
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* <b>TUW-10-12</b> Andreas Ipp, Jörg Evers, Christoph H. Keitel, Karen Z. Hatsagortsyan, ''Streaking at high energies with electrons and positrons'' [http://arxiv.org/abs/1008.0355 hep-th/1008.0355]
  
−  
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* <b>TUW-10-13</b> Daniel Grumiller, Niklas Johansson and Thomas Zojer, ''Short-cut to new anomalies in gravity duals to logarithmic conformal field theories'' [http://arxiv.org/abs/1010.4449 hep-th/1010.4449]
  
−  
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* <b>TUW-10-14</b> Matteo Beccaria, Maximilian Kreuzer and Andrea Puhm, ''Counting charged massless states in the (0,2) heterotic CFT/geometry connection'' [http://arxiv.org/abs/1010.4564 hep-th/1010.4564]
  
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* <b>TUW-10-15</b> C.-M. Chen and Y.-C. Chung, ''On F-theory E<sub>6</sub> GUTs'' [http://arxiv.org/abs/1010.5536 hep-th/1010.5536]
  
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* <b>TUW-10-16</b> P. Anastasopoulos, G. K. Leontaris, R. Richter, A. N. Schellekens, ''SU(5) D-brane realizations, Yukawa couplings and proton stability'' [http://arxiv.org/abs/1010.5188 hep-th/1010.5188]
  
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* <b>TUW-10-17</b> Andreas Ipp, Anton Rebhan, Michael Strickland, ''Non-Abelian plasma instabilities: SU(3) vs. SU(2)'' [http://arxiv.org/abs/1012.0298 hep-ph/1012.0298]
  
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* <b>TUW-10-18</b> M.E. Carrington and A. Rebhan, ''Perturbative and Nonperturbative Kolmogorov Turbulence in a Gluon Plasma'' [http://arxiv.org/abs/1011.0393 hep-ph/1011.0393]
  
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* <b>TUW-10-19</b> Daniel Grumiller, ''Model for gravity at large distances'' [http://arxiv.org/abs/1011.3625 astro-ph/1011.3625]
  
−  
−
* <b>TUW-10-20</b> D. Arnaudov and R.C. Rashkov, ''On semiclassical calclation of three-point functions in AdS_4 x CP^3'' [http://arxiv.org/abs/1011.4669 hep-th/1011.4669]
  
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* <b>TUW-10-21</b> F. Preis, A. Rebhan and A. Schmitt, ''Inverse magnetic catalysis in dense holographic matter'' [http://arxiv.org/abs/1012.4785 hep-th/1012.4785]
  
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=== Previous years ===
  
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: [[Fundamental_Interactions_Preprints_2009|2009]], [[Fundamental_Interactions_Preprints_2008|2008]], [[Fundamental_Interactions_Preprints_2007|2007]], [[Fundamental_Interactions_Preprints_2006|2006]], [http://tph.tuwien.ac.at/~moessmer/preprints05.html 2005], [http://tph.tuwien.ac.at/~moessmer/preprints04.html 2004], [http://tph.tuwien.ac.at/~moessmer/preprints03.html 2003], [http://tph.tuwien.ac.at/~moessmer/preprints02.html 2002], [http://tph.tuwien.ac.at/~moessmer/preprints01.html 2001], [http://tph.tuwien.ac.at/~moessmer/preprints00.html 2000], [http://tph.tuwien.ac.at/~moessmer/preprints99.html 1999], [http://tph.tuwien.ac.at/~moessmer/preprints98.html 1998], [http://tph.tuwien.ac.at/~moessmer/preprints97.html 1997], [http://tph.tuwien.ac.at/~moessmer/preprints96.html 1996]
  
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For published articles, talks, and poster presentations see [[Publications]]
  

Latest revision as of 09:41, 27 April 2021

  • People and activities (← link to current activities and more information on members of the institute with research in Fundamental Interactions, of which the following provides some basic overview)


According to our present knowledge there are four fundamental interactions in nature: gravity, electromagnetism, weak and strong interaction with electromagnetism and weak interaction unified in the electroweak theory. Gravity as well as electromagnetism are macroscopic phenomena, immediately present in our everyday life, like falling objects and static electricity. Weak and strong nuclear interactions, on the other hand, become only important on the microscopic, atomic and subatomic level.

The most important aspect of the strong interaction is that it provides stability to the nucleus overcoming electric repulsion, whereas the transmutation of neutrons into protons is the most well-known weak phenomenon. The aim of fundamental physics may be described as obtaining a deeper understanding of these interactions, and penultimately finding a unified framework, which understands the different interactions as different aspects of a single truly fundamental interaction.


Quantum field theory

Describing the interactions on a more fundamental level the concepts of relativistic quantum field theories are employed. With the advent of quantum mechanics in the first decades of the 20th century it was realized that the electromagnetic field, including light, is quantized and can be seen as a stream of particles, the photons. This implies that the interaction between matter is mediated by the exchange of photons. In turn, matter particles are excitations of further quantum fields which pervade all of spacetime and which produce incessant vacuum fluctuations.

An example of a pure quantum field theoretical phenomenon is the scattering of light by light, which is impossible in the classical theory of electromagnetism. Quantum fluctuations can turn photons fleetingly into electron-positron pairs which can be exchanged with those of other photons. Light-by-light scattering has only recently been observed directly (in ultrarelativistic heavy-ion collisions at CERN), but it also contributes indirectly to other quantum field theoretical phenomena, in particular to the anomalous magnetic moment of elementary particles. The latter can be measured to such high accuracy that it can be used to test the limits of the present Standard Model of particle physics, because even particles that are much too heavy to be produced in present-day particle colliders make their appearance in vacuum fluctuations.

Lbl.jpg     Lblg-2.jpg
Fig.: Light-by-light scattering (photons respresented by wavy lines, charged particles by lines with arrows), and virtual light-by-light scattering in higher-order corrections to the anomalous magnetic moment of charged particles.

Recent research topics at our institute include hadronic light-by-light scattering where the photon couples to strongly interacting particles. The interactions of the latter are too complex to be captured by perturbation theory and Feynman diagrams, requiring new techniques such as gauge-gravity correspondence. The latter is also known as holography, because it is based on the description of a strongly interacting quantum field theory in flat spacetime as sort of a hologram in a higher-dimensional curved spacetime.

A theoretically clean and well studied example of gauge-gravity duality is the so-called AdS/CFT correspondence, where the higher dimensional spacetime is a maximally symmetric negatively curved (anti de Sitter) space and the quantum field theory in one dimension less is a conformal field theory (CFT). Conformal field theories also play important roles in string theory (see below).

  • Highlight: Our involvement in the muon g-2 (in German)


Gravitation

Since the groundbreaking work of Einstein, gravitation is conceived as defining the geometry of spacetime - even defining the very concepts of time and space itself. Planetary motion as well as the motion of massless particles, that is to say light, become the straightest possible paths in a non-Euclidean geometry.

Light-cone representing causal past and future
Fig.: Light-cone of an event representing its causal past and future.

General relativity is a very successful theory. Its predictions range from the deflection of light by massive bodies which distort spacetime (Einstein-lensing) to that of gravitational radiation carrying away energy in the form of "ripples" in spacetime (Hulse-Taylor binary pulsar), as well as to the expansion of the universe (microwave background radiation). One of the most spectacular predictions of general relativity is the existence of black holes, which by now has been confirmed indirectly by numerous astrophysical observations.

Despite of these successes there are several unresolved problems in the physics of gravitation, some of which are considered as the biggest problems in contemporary theoretical physics:

  • The cosmological constant problem entails a gigantic discrepancy (123 orders of magnitude) between observation and naive theoretical expectation, and so far no satisfying explanation exists that resolves this discrepancy.
  • Numerous astrophysical and cosmological observations reveal discrepancies with the theory of general relativity, unless we postulate the existence of dark matter, which so far has not been detected in particle physics experiments.
  • The elusive theory of quantum gravity still is very much a theory under construction, with several conceptual and technical issues seeking for solutions.
  • General relativity predicts its own failure as a consequence of the famous singularity theorems. Physically this means that spacetime contains regions where the curvature grows without a bound. The most prominent examples are the singularities within black holes as well as the Big Bang singularity.

Deeper insights into the structure of physical systems have often been achieved by the imposition of symmetries. This usually breaks the problem down into simpler building blocks which ideally allow a complete solution. Gravity is no exception to this rule since the prototypic black-hole solution, the Schwarzschild geometry (actually the first exact non-trivial solution of the Einstein-equations), has been found precisely along theses lines, i.e. upon imposing spherical symmetry. It is therefore natural to pursue a similar plan of attack for the quantization of gravity. The corresponding models become gravitational theories in a 1+1 dimensional spacetime coupled to the area of the two-sphere which becomes a dynamical variable in the reduced theory. There are several other ways how lowerdimensional (1+1 and 2+1) models arise from higherdimensional configurations in string theory or general relativity, and the description of gravity in lower dimensions is one of the key research fields of our group.


Quark-Gluon plasma

Quantum chromodynamics (QCD) is the accepted theory of the strong interactions responsible for the binding of quarks into hadrons such as protons and neutrons, and the binding of protons and neutrons into atomic nuclei. The fundamental particles of QCD, the quarks and gluons, carry a new form of charge, which is called color because of its triplet nature in the case of the quarks (e.g. red, green, blue); gluons come in eight different colors which are composites of color and anticolor charges. However, quarks and gluons have never been observed as free particles. Nevertheless, because quarks have also electrical charge, they can literally be seen as constituents of hadrons by deep inelastic scattering using virtual photons. The higher the energy of the probing photon, the more do the quarks appear as particles propagating freely within a hadron. This feature is called "asymptotic freedom". It arises from so-called nonabelian gauge field dynamics, with gluons being the excitations of the nonabelian gauge fields similarly to photons being the excitations of the electromagnetic fields, except that gluons also carry color charges. Asymptotic freedom is well understood, and the Nobel prize was awarded to its main discoverers Gross, Politzer, and Wilczek in 2004.

Much less understood is the phenomenon of "confinement", which means that only color-neutral bound states of quarks and gluons can be observed. This confinement can be overcome when the temperature is very large, as, for example, in the first instances of the Early Universe. In this case, quarks and gluons form a quantum fluid that is known as the quark-gluon plasma. Its unique properties are studied on Earth in large collider facilities at LHC (CERN, Switzerland) or at RHIC (BNL, United States), where this plasma is created in ultrarelativistic heavy-ion collision experiments.


phase diagram of quark-gluon matter
Fig.: Qualitative sketch of the expected phase diagram of quark-gluon matter as a function of temperature T and quark chemical potential µ. Solid lines denote first-order phase transitions, the dashed line a rapid crossover.


In our group, we investigate different thermal and nonthermal properties of the quark-gluon plasma, putting particular emphasis on its non-equilibrium early-time evolution shortly after the heavy-ion collision. Using a variety of different techniques, involving perturbative calculations, kinetic theory, hydrodynamics, holography, real-time lattice simulations and artificial neural networks, not only enables us to extract dynamical and universal key features of the plasma, but also to link to other fields of research like machine learning, gravity, the Early Universe and experiments with ultra-cold Bose gases.


String theory

The names of the fundamental forces are related to their strength. The strong force is much stronger than electromagnetism and is thus able to overcome the repulsive force between objects with the same electrical charge (protons or quarks). The weak force is weaker than electromagnetism but still much stronger than gravity. The reason that we almost only recognize gravity in everyday life is that the macroscopic objects are neutral. They don't carry an effective color charge and they carry - if at all - only very small electric charges. For gravity there is no negative charge (negative mass), so that all the small gravitational effects add up to something which is strong enough to move galaxies and build black holes. The seperate description of the forces is quite accurate by now. This is summarized in the standard model of particle physics.

A measure for the strength of a force are the coupling constants of the corresponding theory. They are, however, not constant, but depend on the energy level one is dealing with. If one extrapolates their values to high energies, one discovers that the couplings of electromagnetism, strong and weak force meet at a certain energy level almost in one single point (see Figure 1). This supports the idea that those three forces could be just different aspects of one and the same universal force. There are several theories which try to describe this unification. They are called GUTs, 'grand unified theories'. However, to be really 'grand', such a unification should also include gravity, whose coupling constant is far weaker still at this high energies. The theory, which will manage to unify all forces, including gravity, is sometimes called TOE, "theory of everything". String theory is one candidate, and at present actually the only one for this TOE.

Point particle and closed string interaction
Fig.: Left: Point particle interaction, Right: Closed string interaction, note the smooth interaction surface.


'SUSY' stands for supersymmetry and means that there is an exchange symmetry between fermionic particles (like quarks and electrons) and bosonic ones (like photons and even gravitons, if one includes gravity into the considerations). It does, however, not relate the already known particles, but it predicts new supersymmetric partners to the known particles (called e.g. squarks, selectrons, photinos and gravitinos). So far none of those superparticles has been discovered, but there are a lot of theoretical reasons for believing in supersymmetry. Supersymmetry is an integral part of string theory, or more precisely 'superstring theory'. If supersymmetry is realized at energies not too far above the scale of electroweak symmetry breaking, the Large Hadron Collider at CERN may be able to discover its signatures in its ongoing searches of physics beyond the standard model.


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