## Final Report Summary - CRETEHEPCOSMO (Crete centre for particle physics and cosmology)

The main purpose of the project CRETEHEPCOSMO is to provide a substantial boost to the Crete Centre of Theoretical Physics, a scientifically promising research institution in Heraklion, Crete, Greece in order to arrive at the level of leading European institutions.

This was planned to be achieved by:

- establishing a strong long-term research team of core researchers that are at European level, establish a computational unit and upgrading the hosting facilities for incoming researchers;

- importing new research expertise in key research directions of interest for the Centre via the hiring of experienced researchers;

- being in tune with top research directions and top European groups by exchanging visits and by the organisation of specially targeted research meetings in Crete;

- establish an advisory and evaluation committee that will review the Centre's strategy and activities.

During the project these issues were addressed successfully and in due time.

In particular:

1. Several high quality researchers were hired from top world-wide institutions. They contributed significantly to the enhancement of the research potential.

2. Many visits to and from the partner institutions were made. Strong research and educational ties were built to these institutions, and 6 MoUs of cooperation were agreed and signed.

3. The organisation of important number of high quality and extremely succesful international meetings provided an important visbility boost for the Centre.

4. The Centre has been evaluated and advised from the beginning to the end of the projects by three world class scientists (C. Callan (Princeton), J. Iliopoulos (ENS), G. Veneziano (CERN and College de France)). The final evaluation was very positive.

Several indicators suggest that the impact of the project on the Centre was central and will be long lasting.

Project context and objectives:

The main purpose of the project CRETEHEPCOSMO is to provide a substantial boost to the Crete Centre of Theoretical Physics, a scientifically promising research institution in Heraklion, Crete, Greece in order to arrive at the level of leading European institutions.

This was planned to be achieved by:

- establishing a strong long-term research team of core researchers that are at European level, establish a computational unit and upgrading the hosting facilities for incoming researchers;

- importing new research expertise in key research directions of interest for the Centre via the hiring of experienced researchers;

- being in tune with top research directions and top European groups by exchanging visits and by the organisation of specially targeted research meetings in Crete;

- establish an advisory and evaluation committee that will review the Centre's strategy and activities.

Project results:

A senior postdoctoral researcher was hired (Vassilis Niarchos, PhD Chicago, from Ecole Polytechnique, France) in order to boost the scientific activities of the centre and lead his own research. Niarchos established himself at CCTP, and performed as expected , producing important scientific work, guiding younger researchers both doctoral and postdoctoral, participating in the organisation of the Centre, and organising a very successful July 2012 workshop in Heraklion.

Several other young researchers were hired after a prominent international campaign which attracted about 400 qualified candidates in the field on two occasions.

In the last year, the analogue of 6-7 man-months of postdoctoral fellowships was distributed to a few young researchers that were selected following again an international campaign.

In the meantime a small computational facility was created in order to accommodate the numerical work done by Centre members. The hosting infrastructure was also improved in order to handle the incoming researchers and visitors of the programme.

In order to increase the competitiveness of the Centre, links with nine prominent European institutions are cultivated. Numerous visits and common activities were planned and executed by Centre members to these institutions of related meeting. A vigorous incoming visitor program was also instituted averaging one to two visitors per week that visit the Centre, give seminars on their work and interact with Centre members.

With 6 of the above institutions, namely LPTENS, APC, Arnold Sommerfeld Institute Institute for Theoretical Physics, University of Amsterdam, Theory group, Imperial College, London and Israel Centre of Excellence, specific agreements for cooperation on research and education were signed, setting the guidelines for further cooperation.

Along a different line the opening of the Centre to the physics community abroad was also cultivated by the organisation of workshops and conferences. So far a workshop has been organised in Heraklion focused on major open problems in cosmology linking theory to observations. Some of the top experts in the field attended and directed presentations and discussions. A conference was also organised in Kolymbari, Crete focusing on the broad subject of gauge theories and the structure of space-time.

A second workshop was organised in Heraklion in July 2012, focusing on the gravity theories and their avatars. Finally, the Centre coorganised the sixth Crete regional meeting on string theory in collaboration with the Israel Centre of Excellence, as well as the 6th Aegean School that focused in Quantum Gravity and Quantum Cosmology. All were very successful events.

The Scientists visited the Centre in 2009, at the beginning steps of the project and assessed various aspects of the Centre and its Strategy. The committee visited again the Centre in July 2012 and assessed the implementation of the project, and the results. The first report and the final report can be found at the Centre Website.

Overall all the objectives of the project were achieved to a superlative degree.

The science done during this period at the Centre was diverse, interesting and with impact:

1. AdS / CFT and applications

1.1 Finite density and condensed matter applications

This is a novel topic developed in the last 3-4 years at which the Centre has become one of the world players producing good quality work. There is a lot of expertise on this topic at the Centre.

Some of the topics that were addressed in papers are:

The holography of Schrodinger symmetric systems, with particular focus on finite temperature transport. An intriguing model for strange metal transport at ultralow temperatures has also been constructed that is very close to recent transport and magnetotransport experimental data.

The study of holographic Fermi surfaces in the dilatonic (EMD) backgrounds with and without bulk dipole couplings.

The holographic study of Hall-effect-like physics in D-brane models. It was pioneered by M Lippert and the Technion group, and involved the construction of stable models, by turning on internal fluxes, the study of excitations both standard and magnetic rotons, and the study of stripped instabilities.

The proposal and study in several papers of the Effective Holographic Theory asymptotics in order to classify and study low-temperature holographic physics. It involved a parametrisation of the gravitational theories (EMD), finding near-extremal solutions, and studying their thermodynamics and transport. In this direction, the most general quantum critical geometries with hyperscaling violation have been classified in the U(1) unbroken phase, and the classification in the broken phase is underway.

The calculation of the refractive index in holographic superconductors (which sometimes is negative).

The development of the parity-violating hydrodynamic equations for a charged fluid in 2+1 dimensions to first order in derivatives. There are special terms that were not known before, and were uncovered using holography. In this same direction, the use of action techniques to bypass the derivation of constraints emerging from the entropy current in relativistic hydrodynamics.

The study of holographic fluids with vorticity in 2+1 dimensions based on the TaUb-Nut and Kerr solutions, and their potential application to rotating cold strongly coupled atom gases.

The development of techniques to calculate the quantum effective potential holographically at finite temperature and density. This allows the analytic study of phase transitions in scaling regimes, and the numerical study in any regime. The procedure is currently extended to the rest of the effective action.

A new setup for constructing and studying couplings of holographic QFTs analytically using multitrace deformations. This leads to a new setup for Josephson junctions of holographic superconductors that allows direct calculation of their properties and provides relativistic generalisations of the Gross-Pitaevsky equation. Many solutions here have chaotic behaviour.

Applications to QCD and Heavy-Ion physics

The use of improved holographic QCD, the holographic model developed locally, to compute transport coefficients for the quark gluon plasma, most importantly the bulk viscosity.

The construction and study of simple holographic models for the meson sector, by implementing the characteristics of tachyon condensation from the Sen action to describe chiral symmetry breaking. The models are used in the quenched approximation and are remarkably similar to the real world both at zero and finite temperature.

The natural continuation is to study models in the Veneziano limit. The whole phase diagram emerges with a conformal window, a QCD phase and a BKT / Mirasky conformal transition in between. The thermodynamics and spectra are rich and currently under study.

The correct and improved description of U-shaped brane configurations (relevant for chiral symmetry breaking) using a tachyon action was proposed and tested in the hairpin branes in NS5 backgrounds. This sets up the proper framework for discussing the dynamics of chiral symmetry breaking in SS-like models.

The study of energy loss by heavy quarks in a strongly coupled plasma, by modeling the quarks by strings. The non-conformal characteristics of this energy loss were developed and surprises were found for the Langevin evolution of such heavy quarks at LHC conditions. Technical improvements turned out to be necessary in order to include these calculations into the Monte-Carlo's used in the ALICE experiment.

The study of heavy quark motion in a magnetic field, gave a new perspective on energy loss, and a simple model of time-dependent horizons that can be studied further.

The study of black-hole formation during high energy collisions in non-conformal holographic theories. Trapped surfaces are used to obtain multiplicity estimates together with simplifications for the scale invariance from higher energies. The main tendencies in the energy dependence of the total multiplicity have been explored a model has been proposed that agrees with EHIC data and predicted correctly the data of the first LHC run. Similar computations have been made in theories with compact internal dimensions.

The use of a holography-derived matrix model to describe multi-nucleon bound-states (nuclei), based on the SS model instantons and the investigation of the relevant physics.

The study of 4D YM theory at large N compactified to two dimensions. The phase diagram on anisotropic tori is matched between 2 and four dimensions both using QFT and holographic descriptions. Further the 5D SYM theory was studied, and the expected holographic confinement-deconfinement transition was debunked. A new proposal was made based on the Gregory-Laflamme instability for the transition which gives a new view for the restoration of chiral symmetry in the SS model.

AdS4 / CFT3

The F-maximization principle was analysed in a non-trivial model with N equal to 2 supersymmetry in 3d and new non-trivial checks of the F-theorem were performed. A new criterion for spontaneous supersymmetry breaking in 3d was proposed using localisation techniques and the three-sphere partition function.

Superconformal indices have been used to connect Seiberg dualities in 4 dimensions to analogous ones in 3d.

A direct link between holography and stochastic quantisation was proposed.

A new class of three-dimensional vector models, ( the subdeterminant models) was introduced whose effective potentials exhibit non-standard large-N behaviour. It was argued that the models are relevant for obtaining the effective actions of M2 and M5 branes.

Two dimensional large-N CFTs were analysed and several lessons were learned: they provide examples with a gravity description in AdS3, have an analogue of the reduction of the degrees of freedom at strong coupling and bulk states with multiplicity that is larger than the Cardy entropy.

Gravity and Cosmology

High-energy gravitational scattering

Elastic scattering and gravitational radiation in particle collisions at ultraplanckian energies have been studied. The purpose is to clarify the nature of gravity in the ultraplanckian regime, especially in relation to the gravity "classicalisation" conjecture and also to the black-hole production cross-section.

For the elastic process a straightforward computation of classical scattering of two massive point particles in GR was carried out and reproduced in the ultra-relativistic regime the result obtained by other authors with different techniques, namely shock wave scattering ('t Hooft), or leading eikonal approximation in the context of quantum gravity (by Giudice, Rattazzi, Wells), or string theory.

The same pedestrian classical approach was used to compute scalar, vector, or gravitational radiation emitted in ultraplanckian collisions of particles interacting gravitationally. The preliminary result was that in collisions of massive particles and for impact parameter ?? Schwarczshild radius, for large enough collision energy practically all available energy is emitted away.

This result is currently under intensive scrutiny and extension in various directions.

Gravitational backreaction and quantum effects in inflation

A detailed study of the phenomenological consequences of the quantum gravitational back-reaction to inflation was done. This resulted in the construction of cosmological models with novel features, like the enhancement of very high frequency primordial gravitational waves.

A further study of the "Feynman rules" for the graviton in de Sitter spacetime was also performed. This resulted in the construction of the graviton propagator for general invariant gauges.

Black holes and blackfolds

Black brane solutions in higher dimensional theories of gravity play a key role in our general understanding of gravitational theories and gauge-gravity dualities. Niarchos has developed (together with Emparan, Harmark and Obers) a general effective field theory description of the long-wavelength dynamics of black branes known as the blackfold approach. This general hydrodynamic formalism of black holes has been extended recently to describe black brane intersections in generic (super)gravity theories and has been applied to a perturbative construction of new extremal and non-extremal black holes with exotic horizons, multiple charges and dipoles in string / M-theory.

An innovative use of the blackfold formalism to the M2-M5 intersection in M-theory has produced a remarkable result: the first ever calculation of the central charge of the second CFT at the M2-M5 intersection.

The physics of Lorentz violation

Gravity theories of the Hoava-Lifshitz type

This class of gravity theories have broken part of the diff invariance, and a Lifshitz scaling ultraviolet physics. They were proposed as renormalisable alternatives to standard gravity. An analysis of the HL cosmology has been done, and it was pointed out the the UV scaling symmetry provides several ingredients that make inflation unnecessary. There is no horizon problem, the flatness problem is much milder, and there is a natural source of scale invariant cosmological perturbations.

Spherically symmetric solutions were analysed in the original HL gravity theory, and the most general such solution was found. Although generic solutions have 1 / r tails, several special ones are different, including the one with detailed balance. The modified geodesics in such solutions were formulated and shown that they have no horizons.

Spherically symmetric solutions were analysed in the modified HL gravity theory proposed by Blas et al. This is a more complicated theory that is however in agreement with existing data. The solutions have generic 1/r tails except when the cosmological constant is present. These solutions are identical to those of 'Einstein-Aether' theory.

Lorentz violation in strongly coupled QFTs

Study of the energy loss / disipation in LV contexts due to Cerenkov radiation. Employing recent results from holographic LV scaling geometries in condensed matter contexts a general study of energy loss is made and the possibilities have been classified.

String Phenomenology

The subject of mass hierarchies in orientifold vacua was addressed by studying the U(1) symmetries associated with SM embeddings. These together with symmetry breaking and string instantons, classify the patterns of hierarchies. Several such patterns were found that agree with what we have in the SM.

The Yukawa couplings in orientifold realising SU(5) unified gauge symmetry were analysed generically. It was found that instanton effects that are necessary in order to generate top quark masses generate also unacceptable operators that mediate fast proton decay.

Other

Studies of technicolor theories at finite temperature and a calculation of the correlation between f and Tc for chiral symmetry restoration.

Studying the phenomenological signatures of technicolor theories at LHC and linear colliders.

Calculation of Hilbert series of N equal to 1 sQCD with SU(N) gauge group.

A proposal for holography in the Einstein framework with cosmological constant.

An analysis of gauge theory holographic physics and confinement criteria in FRW cosmological geometries.

Distinctions

Distinguished professor D. Christodoulou was awarded the Shaw prize for the Mathematical Sciences, shared with Prof. R. S. Hamilton. The prize was given for their highly innovative works on nonlinear partial differential equations in Lorentzian and Riemannian geometry and their applications to general relativity and topology.

CCTP Postdoctoral researcher T. Morita, was awarded the 'Young Scientist Award of the Physical Society of Japan' for his work on the phase structure of compactified YM.

The paper Int.J.Mod.Phys. D20 (2011) 2847-2851 by Tsamis and Woodard received an honourable mention from the Gravity Research Foundation.

- The paper arXiv:1204.2029 [hep-th] by Zhang+Wu+Tiang, received an honourable mention from the Gravity Research Foundation.

The paper Class.Quant.Grav.26:105006,2009 by Tsamis+Woodard has been highlighted in 2009 by the Journal of Classical and Quantum Gravity

The paper Nucl.Phys.B821:467-480,2009 by Kiritsis+Kofinas was among the 50 most cited papers in 2009. Today it has 249 citations in SPIRES.

The papers Phys.Rev.Lett.101:181601,2008 and Nucl.Phys.B820:148-177,2009 by Gursoy+Kiritsis+Mazzanti+Nitti were highlighted in Physical Review Focus on the occasion of a recent high-precision lattice calculation in Large N gauge theory.

Potential impact:

1. An important enhancement of the capacity of the Crete Centre for Theoretical Physics to do cutting-edge research at a level comparable with high quality Universities in the EU and elsewhere.

2. An important enhancement in the visibility of the Centre vis a vis the scientific community. In particular CCTP has the ability now to attract top researchers from abroad, to come and do research at the Centre.

3. An important enhancement in the organisation of the Centre and its services that compensate the complete non-man's-land that exists in Greece when it comes to hosting long term foreign researchers. This structure has been diffused to the whole of the University of Crete.

4. An important enhancement of the outreach activities of the Centre, geared towards high-school students, their teachers and the public at large.

Such results put CCTP a model institutions in the country and provide a visible benchmark for institutions locally and nationwide, especially in a period where the country is suffering from many serious problems.

Scientific attractiveness of the Centre

We do have in the last 3 years an increased number of postdoctoral applicants: 5 years ago (although we were accepting applications via the Leuven European site) we had a small number of people that would put us as their first choice. This has increased dramatically in the last 3 years, with the exception of this year, for which the only plausible interpretation is the impact of the Greek crisis in the minds of young researchers.

We do have a fair number of postdocs who contact us to make Marie Curie applications to come to Crete. 5-8 years ago this number was 1-2 per year. Now we have 10-20 people every year who ask and we have to choose.

We started having postdocs who would like to come to CCTP with their own funding. One Italian (Also Cotrone) and one Spaniard (Daniel Arean). Eventually, they have obtained standard postdoctoral positions with much higher salary in other good places and they preferred to go there.

The number of foreign applicants for PhD has moved up from 0-6 years ago to about 20 now.

We have had the ability very recently to hire from the top of our short lists something that was not the case before when we nneded to go as far down as 10th place.

The scientific output of the CCTP has increased in the last 3 years. In terms of papers, there are so far:

2008: 19 papers by core CCTP members (12 by core faculty members).

- 2009: 19 papers by core members (14 by core faculty members), and 25 by adjuct members.

- 2010: 31 papers by core members and (17 by core faculty members), 27 by adjuct members.

- 2011: 45 papers by core members (17 by core faculty members) and 34 by adjuct members. -

2012: 19 papers by core members up to May (10 by core faculty members).

There is a correlation with total personnel, however the numbers of core faculty papers are however indicative of the progress.

We have more invitations to conferences and workshops. These are the coordinators? data below (plenary talks in conferences or workshop presentations).

- 2012 (10 conferences / workshops).

- 2011 (5 conferences / workshops).

2010 (11 conferences / workshops).

- 2009 (7 conferences / workshops).

- 2008 (9 conferences / workshops).

- 2007 (7 conferences / workshops).

- 2006 (8 conferences / workshops).

- 2005 (9 conferences / workshops).

- 2004 (3 conferences / workshops).

- 2003 (5 conferences / workshops).

The numbers are steadily increasing, but an important difference between 2003 and 2012, is that E.Kiritsis in 2003 accepted all such invitations while in 2012, he accepted only one in three invitations on average. The progress is clear.

In the last 3 years, Centre members were invited to co-organise meetings elsewhere. This did not happen before with one exception.

There was an enhanced effort in the last 3 years to prepare and submit FP7 and other proposals:

- 4 ERC proposals (1 partly successful, funded by GREECE).

- 14 Marie Curie fellow proposals (5 successful) and 6 under current review.

- 2 Marie Curie network proposals (none successful, the topic, string theory was ?blacklisted? by the appropriate pannel).

- 1 COST proposal (in progress, passed original marks).

- 1 ESF proposal (successful overall but no money from Greece).

- Outreach: We have set up our website, and we communicated it to all high schools in Greece last October 2011. Since then, we have about 1000 people approximately that read it.

Our CCTP website was monitored since the last year:

- from May 2011 to end 2011 we obtained 5526 hits and 4185 visitors out of which 1628 were new;

- from January 2012-August 2012 we obtained 6474 hits and 5031 visitors out of which 2035 were new.

List of websites: http://hep.physics.uoc.gr/CRETEHEPCOSMO/CRETEHEPCOSMO.shtml