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| TS11 EXPERIMENT, RESPONSIBLE: Loriano Bonora |
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Here are some headings for the topics recently covered by the IS:
1) STRING AND BRANE THEORIES AND THEIR DUALITIES.
2) QUANTUM GRAVITY, COSMOLOGY AND BLACK HOLES.
3) GAUGE FIELD THEORIES.
4) 2D and other FIELD THEORIES.
The IS involves almost 60 researchers from ten INFN sections. During the last year almost 100 papers have been produced. Here is a short summary of the recent research activity.
STRING AND BRANE THEORIES.
Research in string inspired gauge field theories has been carried out in Padova, Roma1 and Roma2 (Seiberg duality, generalized Seiberg-Witten N=2 theory, Seiberg-Witten prepotentials).
An important research subject has been as always the AdS/CFT duality and its developments. This has been carried out especially in Roma2 (properties of SYM composite operators) and Trieste (developments of the LLM proposal on bubbling AdS).
A third relevant topic has been tachyon condensation and string field theory, a type of research carried out in Trieste.
Under the heading of string theory we can perhaps classify the intense activity in higher spins fields dynamics, which has continued in the last period, both in Padova, Pisa and in Roma2 and Trieste.
Flux compactifications. This subject has been a hot topic worldwide in recent years. In our initiative significant contributions in this regard have come from Padova and,
especially Roma2 (flux compactification on tori).
Pure spinors. This subject is acquiring momentum. There has been intense activity both in Padova and Roma2.
Topological strings and membranes. This subject is a new entry. It has been developed in Trieste.
The activity in string theory is not limited to the above topics. There have been other significant contributions. A vast activity on brane dynamics, brane on curved backgrounds and brane with fluxes, has been carried out in Rome2. In Pavia there has been an intense activity on open-closed string duality.
QUANTUM GRAVITY, COSMOLOGY AND BLACK HOLES.
This is a very lively subject in our initiative. The Bologna group is very active in three main directions: quantum field in curved space-time and black-hole evaporation; acoustic black-holes; black-holes and cosmology in braneworlds. Another active group in this subject is the Pavia one (research on dynamical triangulated manifolds and on the holographic principle in 4D). There have been various contributions in Roma1 on canonical non-commutative space-time and on loop quantum gravity. Finally one should mention the application of RG in quantunm gravity in Trieste and the research on gravitational helicity interactions in Pisa.
GAUGE THEORIES
This is also a very important research ground. Of course many of the subjects already mentioned could be classified under this heading. But there are specific contributions, which come from Milano and Rome1: works on exact renormalization group and research on large N QCD in Roma1, and on BF theories and Hopf algebra structure of the relevant Feynman graphs in Milano.
2D and other FIELD THEORIES.
Conformal and integrable field theories form the common background of many developments in string and brane theories and gauge theories. However sometime they are studied on their own. This is the case of (integrable) field theories with impurities and finite temperature field theories with defects in Pisa, the t-J model (Padova) and WZW models in TS. A subject that is taking up momentum is quantum computation: Milano and especially Pavia are active in this area.
PROGRAM FOR THE FUTURE.
The research programs for the future are mostly a prolongation of the past activity. Many themes will keep being among the most popular ones. This is the case for AdS/CFT correspondence and, especially, the properties of N=4 SYM theories in 4D, open-closed string duality and gauge-gravity correspondence, topological strings, higher spins, pure spinors, properties of supersymmetric field theories, exact renormalization group, field theory models with defects, noncommutative spaces, quantum computing. An increasing role of black hole physics and cosmology is expected.
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The aim of this IS is to form a common area where problems at the intersection of gravity, field theory and string theory are investigated. Therefore the main purpose of our IS is the exchange of ideas and the cross-fertilization among nearby areas of research. In recent years string theory has become a popular unifying tool for gravity and particle physics. However at this right moment the prevailing attitude is a reflexive one. On the one hand the difficulties met by string theory suggest that perhaps it has be put under more careful scrutiny. On the other hand we are waiting for some crucial experimental results, especially those from the LHC, which may reorient the research in high energy physics. This state of suspension favors new attempts and approaches and the reappraisal of old tools and theories. We believe this moment is particularly favorable to the interdisciplinary attitude of our IS. The latter meantime has evolved. It can be said that it is now predominantly (although not exclusively) oriented to gravity theories, dealt with both with traditional field theoretic and string theoretic methods. It is no accident that the most visited research topic has become black hole physics. Here anyhow is a list of the most prominent ones: acoustic black holes, Hawking radiation, Kerr/CFT duality, cosmological singularities, asymptotically safe gravity, YM/string duality, noncommutative space-times, string field theory and open-closed string duality, Ricci flow, Chern-Simons theories, topological field theory and quantum computation, quantum wires and applications, holographic approach to condensed matter systems.
From the organizational point of view we plan to have periodic meetings of the IS participants, and a biennial meeting with other contiguous IS's.
Going now to our concrete scientific program, the main (present and future) research subjects are, section by section, the following ones.
BOLOGNA.
Bose-Einstein condensate and Hawking radiation (R.Balbinot).
For their high coherence, the low temperature and the surprisingly high technology in handling them, Bose-Einstein condensates (BEC) are so far the most promising candidate to build a concrete setting in condensed matter physics for detecting the analogue of Hawking radiation. The new idea we have developed in this area lies in the study of the
correlations between Hawking partner particles. In fact Hawking radiation consists in the production of particles in couples: one located inside the horizon and falling into the hole, the other escaping and eventually reaching far observers. This Hawking couple shows peculiar quantum correlations. While in gravitational black holes the simultaneous
detection of IN/OUT partners is impossible, this is not true any more in the acoustic setting, since the IN/OUT regions are not causally disconnected: a simultaneous easurement is possible. This fact can be of great importance, since the measurement of correlations is much easier than the detection of single particles. As we have shown, after a transient due to the horizon formation (Dynamical Casimir), a characteristic peak appears in the correlation function in correspondence of the position of the two partners. The signal appears not too low and we have also studied a way to amplify it by modifying (lowering) the coupling between the atoms.
This should make its experimental detection more easy.
PAVIA
(i) Ricci flow, QFT and the renormalization group:
Recent advances in Ricci flow theory have a potential impact in addressing 2D Quantum Field Theory. We have been analyzing this issue in depth providing some new results related to a Green function representation of the backward Ricci flow (corresponding to the UV regime for the associated renormalization group in QFT). In particular we have analyzed the geometrical landscape of non linear sigma model in the strong curvature regime.
(ii) Topological Quantum field theory and quantum computation.
We have continued the investigation of the properties of a scheme for quantum computation based on modular functors of the Chern-Simons theory realized by the recoupling theory of N SU(2) angular momenta. This research theme will be continued next year.
PISA
1. Chern-Simons quantum field theory:
We are considering the topological quantum field theory defined by the Chern-Simons action and the path integral computation of certain topological invariants in ontrivial 3-manifolds. The possible interplay between the abelian and the non abelian link invariants, the dependence of the invariants on the homology and on the homotopy type of the manifold are being investigated.
2. Quantum wires and time reversal:
We explore the possibility to break time reversal invariance at the junction of quantum wires. The universal features in the bulk of the wires are described by the anyon Luttinger liquid. A simple necessary and sufficient condition for the breaking of time
reversal invariance is formulated in terms of the scattering matrix at the junction. The phase diagram of a junction with generic number of wires is investigated in this framework. We give an explicit classification of those critical points which can be reached by bosonization and study the interplay between their stability and symmetry content.
3. Anyonic Luttinger junctions:
Anyonic Luttinger liquids wires joining at a single point are investigated. Using some simple results from the spectral theory of differential operators on graphs, we have solved the model exactly. This allows to reach some of the critical fixed points in the low momentum regime. The stability of these fixed points is analyzed.
ROMA1.
TS11 at Roma1 has continued work on "the pure Yang-Mills/string-theory correspondence" [Bochicchio], "Mathematical foundations of the replica method in spin-glasses" [Guerra] and "Non-commutative QFT and its applications" [Amelino-Camelia].
Bochicchio has made further progress in characterizing the pure Yang-Mills/string-theory correspondence codified in an exact beta function in the large N limit, on the Yang-Mills side, by means of homological localization in the loop equation. In particular, he has computed the exact beta function and the glueball spectrum in large-N Yang-Mills theory.
Amelino-Camelia has continued his work on the Noether analysis of the Hopf-algebra spacetime symmetries of theories in the "kappa-Minkowski" and "canonical" noncommutative spacetimes, as well as on the formalization of an "area observable" for noncommutative spaces He has also initiated a study (Phys.Lett.B686:283-287,2010) of the fate of spacetime symmetries in the general framework of Horava-Lifshitz theories.
TRIESTE.
String Field Theory (L.Bonora).
In recent years, via the Sen conjectures, string field theory has become a privileged ground to analyze tachyon condensation. The solution found by Schnabl, which identifies exactly the tachyon condensation vacuum, has redirected all the research in this field. In our Unit a research program has just been completed for the search of such solutions in the oscillator formalism. The aim is to prepare the ground for finding many other solutions like Schnabl's one. Indeed string field theory is the most advanced attempt to formulate string theory in a complete and consistent way, that guarantees its UV completion. In the face of such vast program it is extremely important to know whether this theory possesses 'enough classical solutions' to be up to its ambitions.
Hawking radiation and anomalies (L.Bonora).
In the wake of the abundant literature concerning the calculation of the Hawking flux by means of anomalies, we have completed the study of the relation between the W(infinity) algebra of currents and the structure of the thermal spectrum of the Hawking radiation by considering the case of the Kerr black-hole and the fermionic currents. This study confirms the results previously found for the case of the Schwarzschild BH.
Spinning black holes, (C.Krishnan)
Spinning black holes offer a tractable situation in our quest for an understanding of time dependent backgrounds in a fundamental theory. Since AdS/CFT provides a strategy for probing the internal structure of black holes, we have investigated what it has to say about spinning black holes in AdS. The conclusion in the three-dimensional case is that regions beyond the Cauchy horizon are excised in the full quantum theory, and that when
perturbed, the inner horizon settles down as a singularity.
A recent related development regarding spinning black holes is the Kerr-CFT correspondence. It was shown by Castro, Maloney and Strominger that 4 dimensional Kerr black holes have a hidden conformal symmetry. Since the Kerr black hole is a rather simple black hole, it is important to see whether this phenomenon is special to Kerr or
a generic feature of black holes. We have showed that for a very generic class of black holes in string theory, this hidden conformal symmetry indeed exists.
Holographic approach to Condensed Matter Systems (C.Krishnan).
The work on AdS/condensed matter (in collaboration with D. Arean and P. Basu) has shown that the phase structure of 3+1 dimensional holographic superfluids is quite different from that of 2+1 dimensional superfluids which have previously been investigated in the literature. We have found a very rich structure in 3+1 dimensions including new uperconduting regions and new phase transitions depending on the mass of the condensate. We have also developed an asymptotic method for investigating phase structures of holographic superfluids, which is fully analytic in 3+1 D. We expect that the 3+1 dimensional case will be of relevance in studying realistic superluids as well as the phase structure of QCD.
Cosmological Singularities and String theory (Lorenzo Seri)
We want to understand how much we can learn about the physics of such singularities in a string theoretical frame. In particular we are working on an extension of the CSV matrix Big-Bang to some special backgrounds, Singular Homogeneous Plane Waves (SHPWs). The extension of DLCQ (Discrete Light-Cone Quantization) to such backgrounds has led us to study a non-Abelian gauge theory with time-dependent coupling, where the space-time coordinates are represented by generally non-commuting matrices: in particular we have focused on the case of strong coupling singularities, namely when the string coupling blows up as the singularity t=0 is approached. Conversely in the same limit the yang-Mills coupling goes to 0, so the standard lore is that near the singularity the geometry of space-time is non-commuting, while as we go to large times the growth of the Yang-Mills coupling forces the coordinates to choose a commuting configuration and ordinary flat space-time is recovered. In order to test both these limits, we have built a toy model that would retain the basic features of our non-Abelian time-dependent theory, and we investigated the behavior of its solutions both at classical and quantum mechanical level. The first results are the following: as t goes to 0 the non-Abelian quartic interaction becomes negligible and all the modes (diagonal and off-diagonal) decouple; at large times the coordinates do not choose a particular commuting configuration but they bounce amongst all the possible ones.
Asymptotically safe theories (R.Percacci).
This line of research involves calculations of beta functions using functional renormalization group methods, with the long term aim of proving the conjecture that gravity, or gravity coupled to matter, is asymptotically safe.
Recent calculations in this directions have targeted the following systems:
- topologically massive gravity in 3d (with E. Sezgin)
- gravity in 4d coupled to scalars with potential interactions and fermions with Yukawa interactions (with Narain, Zanusso and Vacca)
- nonlinear sigma models with two and four derivative terms, a system that is very similar to higher derivative gravity (with Zanusso).
Another line of research is the construction of unified theories of gravity where the gravitational connection is put in a multiplet with Yang-Mills fields describing the other interactions. Recently we have shown (with F.Nesti) that one can construct a fully realistic fermionic sector for one such theory based on the group SO(3,11).
Theory of invariants (V. Talamini)
We have studied topics of the theory of invariants of compact (continuous or finite) groups, and in particular the orbits of compact groups. The aim of this research is the study of spontaneous breakdown of symmetry in many fields of physics such as grandunified theories, superstring theories as well as phase transitions in cristalline systems.
ATTIVITA' PREVISTA PER L'ANNO 2011
The aim of this IS is to form a common area where problems at the intersection of gravity, field theory and string theory are investigated. Therefore the main purpose of our IS is the exchange of ideas and the cross-fertilization among nearby areas of research. In recent years string theory has become a popular unifying tool for gravity and particle physics. However at this right moment the prevailing attitude is a reflexive one. On the one hand the difficulties met by string theory suggest that perhaps it has be put under more careful scrutiny. On the other hand we are waiting for some crucial experimental results, especially those from the LHC, which may reorient the research in high energy physics. This state of suspension favors new attempts and approaches and the reappraisal of old tools and theories. We believe this moment is particularly favorable to the interdisciplinary attitude of our IS. The latter meantime has evolved. It can be said that it is now predominantly (although not exclusively) oriented to gravity theories, dealt with both with traditional field theoretic and string theoretic methods. It is no accident that the most visited research topic has become black hole physics. Here anyhow is a list of the most prominent ones: acoustic black holes, Hawking radiation, Kerr/CFT duality, cosmological singularities, asymptotically safe gravity, YM/string duality, noncommutative space-times, string field theory and open-closed string duality, Ricci flow, Chern-Simons theories, topological field theory and quantum computation, quantum wires and applications, holographic approach to condensed matter systems.
From the organizational point of view we plan to have periodic meetings of the IS participants, and a biennial meeting with other contiguous IS's.
Going now to our concrete scientific program, the main (present and future) research subjects are, section by section, the following ones.
BOLOGNA.
Bose-Einstein condensate and Hawking radiation (R.Balbinot).
For their high coherence, the low temperature and the surprisingly high technology in handling them, Bose-Einstein condensates (BEC) are so far the most promising candidate to build a concrete setting in condensed matter physics for detecting the analogue of Hawking radiation. The new idea we have developed in this area lies in the study of the
correlations between Hawking partner particles. In fact Hawking radiation consists in the production of particles in couples: one located inside the horizon and falling into the hole, the other escaping and eventually reaching far observers. This Hawking couple shows peculiar quantum correlations. While in gravitational black holes the simultaneous
detection of IN/OUT partners is impossible, this is not true any more in the acoustic setting, since the IN/OUT regions are not causally disconnected: a simultaneous measurement is possible. This fact can be of great importance, since the measurement of correlations is much easier than the detection of single particles. As we have shown, after a transient due to the horizon formation (Dynamical Casimir), a characteristic peak appears in the correlation function in correspondence of the position of the two partners. The signal appears not too low and we have also studied a way to amplify
it by modifying (lowering) the coupling between the atoms. This should make its experimental detection more easy.
For next year we plan to study Hawking like emission in BECs with Black Hole and White Hole configurations with particular emphasis on the stability/instability of the latter.
PAVIA
(i) Ricci flow, QFT and the renormalization group:
Recent advances in Ricci flow theory have a potential impact in addressing 2D Quantum Field Theory. We have been analyzing this issue in depth providing some new results related to a Green function representation of the backward Ricci flow (corresponding to the UV regime for the associated renormalization group in QFT). In particular we have analyzed the geometrical landscape of non linear sigma model in the strong curvature regime. The purpose for the near future is to use such Ricci flow framework in order to analyze c-theorems.
(ii) A new subject we would like to start is the analysis of dark energy by means of geometrical averaging.
(iii) Topological Quantum field theory and quantum computation.
We have continued the investigation of the properties of a scheme for quantum computation based on modular functors of the Chern-Simons theory realized by the recoupling theory of N SU(2) angular momenta. This research theme will be continued next year.
PISA
1. Quantum graphs modeling quantum wires:
Quantum graphs are networks of one-dimensional wires connected at nodes. For the first time such structures have been applied some decades ago to describe the electron transport in organic molecules. Due to the impressive progress in nanotechnology such devices can be constructed and tested nowadays in laboratory. On the theoretical side, the quantum behavior of these essentially one-dimensional systems involves a series of interesting physical problems in the context of both quantum field theory and string theory:
(i) interacting one-dimensional electron gas and conductance properties of quantum wires;
(ii) bosonization and vertex algebras on quantum graphs;
(iii) study of quantum graphs with dissipative vertices.
(iv) string theory: the appearance of BPS configurations in which three strings meet at a point is well known, but poorly investigated. Using this three string configuration one can construct string networks and, applying the methods of quantum graphs, investigate their properties.
2. Study of the transport properties of quantum wire junction away from equilibrium:
Construction of nonequilibrium steady states on quantum wire junctions and derivation of the associated steady currents describing the charge, energy and entropy flows.
3. Chern-Simons theory and link invariants in generic closed orientable 3-manifolds:
Application of the Chern-Simons gauge theory for computation of link invariants.
ROMA I.
Yang-Mills/String Theory (Bochicchio)
In the last years this theme has always been present in our IS. Recently further progress has been made in characterizing the pure Yang-Mills/string-theory correspondence codified in an exact beta function in the large N limit, on the Yang-Mills side, by means of homological localization in the loop equation. In particular, the exact beta function and the glueball spectrum in large-N Yang-Mills theory has been computed. The intention is to further exploit the application of the homological localization formula for the loop equation for new developments. (see Bochicchio's JHEP 0905:116,2009).
Non-commutative space times (Amelino-Camelia).
Noether analysis of the Hopf-algebra spacetime symmetries of theories in the "kappa-Minkowski" and "canonical" noncommutative spacetimes, as well as the formalization of an "area observable" for noncommutative spaces have been the object of the most recent research in the area of non-commutative spacetimes. A key objective for the near future will be showing the applicability of the techniques of the above Noether analysis of Hopf-algebra spacetime symmetries also to the case of more realistic theories (so far only Klein-Gordon fields have been analyzed).
Mathematical foundation of the replica methods (F.Guerra)
The study on the mathematical foundations of the replica method in spin-glasses will be continued.
TRIESTE
String Field Theory (L.Bonora)
A. Sen has suggested that closed string theory (in the presence of D-branes) should be expressible in terms of open string theory modes. In other words it would seem that closed string theory should be regarded as an effective theory. This conjectured open-closed string relationship constitutes an ongoing research theme. A few years ago M.Schnabl was able to find an analytic solution that singles out the tachyon condensation vacuum, starting from the unstable vacuum where the theory is initially quantized. This solution has opened new prospects. However in order to discuss such issues as open-closed duality it is necessary to find more solutions of the type Schnabl has found, in fact something like a 'complete' set of solutions. Recently we have completed a program that opens the way to the search for such solutions by means of the oscillator formalism (the formalism used by Schnabl and most of the people working on the subject is CFT). The reason why we intend to use this language is the parallelism with vacuum string field theory (a simplified version of OSFT), where the oscillator formalism allows for an elegant classification of the solutions, which seem to be particularly fit for studying the open-closed string duality. The next objective is to search the 'lump' and multi-brane solutions, which are the basis to study open-closed string duality. A further subject is the natural generalization of the previous project to supersymmetric string field theory.
Kerr-CFT Duality (L.Bonora. C.Krishnan)
This is a recently discovered (and still partly conjectured) duality between a near horizon extreme Kerr black hole geometry and a related asymptotic CFT theory. This idea, proposed by A.Strominger and collaborators, has become the object of an intensive research activity and has undergone various degrees of generalizations. Lately it has been shown that away from extremality such duality still holds, but only in the solution space of the wave equations of the propagating fields in the given (non-extremal) geometry. This property is however enough to ensure duality. So far such property has been verified only for the scalar field. We would like to generalize it to other fields.
Another project (with J. Wang) is to investigate the origin of dimensionful temperatures in the Kerr-CFT correspondence.
Holographic approach to Condensed Matter Systems (C.Krishnan).
One project is to construct a full-realization of a holographic superfluid in type IIB string theory (with D. Arean, M. Bertolini and T. Prochazka). In another project (with J. Evlsin) we are constructing vortex solutions of 2+1 dimensional conformal fluids. In a work with D. Arean, E. Conde and A. Ramallo, we are constructing a IIB supergravity dual of an N = (1, 0) supersymmetric two dimensional gauge theory.
Cosmological Singularities and String theory (Lorenzo Seri)
We want to understand how much we can learn about the physics of cosmological singularities in a string theoretical frame. In particular we are working on an extension of the CSV matrix Big-Bang to some special backgrounds, Singular Homogeneous Plane Waves (SHPWs). In particular we have focused on the case of strong coupling singularities, namely when the string coupling blows up as the singularity t=0 is approached. Conversely in the same limit the Yang-Mills coupling goes to 0, so the standard lore is that near the singularity the geometry of space-time is non-commuting, while as we go to large
times the growth of the Yang-Mills coupling forces the coordinates to choose a commuting configuration and ordinary flat space-time is recovered.
Currently we are trying to understand in a toy model in what sense ordinary space-time can be recovered and to make some progress in the description of the singularity. To do this, we are exploring several possible regularizations of the singularity, discussing what could be physically sensible. We would like also to find out if something quantitative can be said about the singularities whose Penrose limits are SHPWs, as such singularities form a large class including e.g. FRW and Schwarzschild.
Asymptotically safe theories (R. Percacci)
In the long run, one would like to have an asymptotically safe theory of gravity coupled to the standard model or, better still, an asymptotically safe unified theory including gravity. One will have to approach this goal by studying increasingly more complete and realistic systems. In the next year we plan to study mostly extensions of the previous work, such as the study of the effect of anomalous dimensions, and the simultaneous coupling of gravity, gauge and matter fields. Another related line of research that we plan to pursue is to look for applications of asymptotic safety within the standard model (without gravity), in particular gauged nonlinear sigma models and semi-realistic higgsless versions of the standard model.
Final Report.
This IS will terminate this year. It has been operative for 29 years.
Its nature has always been interdisciplinary, at the intersection of
gravity, field theory and string theory. It has produced thousands of
papers and accompanied the careers of many tens of researchers and
launched tens of young ones. The initial motivation (in the early 80's)
was to foster the application of modern mathematics in field theory,
in a national panorama which was almost impregnable to modern
mathematical methods. This proved to be a right investment: advanced
mathematical methods in theoretical physics are overwhelming nowadays
and the cross-fertilization of advanced physical and mathematical
ideas are one of the most fruitful results of the last thirty years
of research. We think we have contributed to it with the present IS,
at least as far as the national panorama is concerned.
As for the present, we are still expecting crucial experimental results,
hopefully from the LHC, which may reorient the research in high energy
physics. This state of suspension must favor new attempts and approaches
and the reappraisal of old tools and theories. For this reason I believe
this moment is particularly favorable to an interdisciplinary attitude,
like the one of our IS. The people in charge of the scientific policy
in high energy physics had better take this fact into due account.
As a national coordinator if this IS, I would like to thank all the
participants, old and recent ones, for their collaboration. We have
done a good work. We must be proud of it.
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Istituto Nazionale di Fisica Nucleare - Piazza dei Caprettari, 70 - 00186 Roma
tel. +39 066840031 - fax +39 0668307924 - email: presidenza@presid.infn.it
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