### University of Crete HEP Seminars

**
Emergent gravity from hidden sectors
**

Speaker: | Elias Kiritsis |

Institution: | University of Crete |

Time: | Tuesday 5 February 2019, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | Gravitons as composite particles have been entertained since a long time, without a lot of succes. We revisit this idea motivated by the AdS/CFT correspondence. We show that hidden theories coupled to the SM may provide an emergent graviton, that is a composite of the hidden fields. This is a more general phenomenon beyond holographic theories. We explore the general setup and find that UV-sourced interactions of the stress tensor give rise to an emergent graviton in the IR. We study the general properties of such gravity, both in the linearized and the non-linear approximation. We show that generically there is an emergent (exact) diffeomoprhism invariance and the graviton is therefore ``massless" but the cosmological constant is generically non-zero. |

**
Soft photon production and entanglement
**

Speaker: | Nicolaos Toumbas |

Institution: | University of Cyprus |

Time: | Thursday 7 February 2019, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | TBA |

**
Emergent/Composite axions
**

Speaker: | Pascal Anastasopoulos |

Institution: | University of Vienna |

Time: | Tuesday 12 February 2019, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | Hidden theories coupled to the SM may provide emergent axions, that are composites/bound-states of the hidden fields. This is motivated by paradigms emerging from the AdS/CFT correspondence but it is a more general phenomenon. We explore the general setup and find that UV-sourced interactions of instanton densities give rise to emergent axions in the IR. We study the general properties of such axions and argue that they are generically different from both fundamental and composite axions that have been studied so far. |

**
Effective Potential for Revolving D-branes
**

Speaker: | Hikaru Ohta |

Institution: | KEK, Tsukuba |

Time: | Tuesday 19 February 2019, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | D-branes in the superstring theory are widely used in the string phenomenology and cosmology. While it is interesting to consider the moving D-branes, we don't understand the dynamics of D-branes well enough especially when they are accelerating. In particular, it is important in the brane-world scenario to know if the stable bound states exist. As a first step, we consider a pair of D0-branes of bosonic string theory which revolve around each other in the flat spacetime. We quantize the system perturbatively with respect to the velocity of the D -branes and determine the one-loop partition function of the open string, from which we extract the short-distance behavior of the effective potential for the revolving D0-branes. |

**
Holographic RG flows for exactly solvable model.
**

Speaker: | Anastasia Golubtsova |

Institution: | BLTP JINR, Dubna, Russia |

Time: | Tuesday 5 March 2019, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | In this seminar I will consider a gravity model with a dilaton potential given in terms of exponential functions. The form of the potential allows to reduce EOM to Toda chains and find exact solutions.The solutions can be interpreted as domain walls interpolating between different asymptotics, and as such they can have interesting applications in holography. We found solutions which interpolate between an AdS fixed point in the UV limit and a hyperscaling violating boundary in the IR region. We also find analytic black brane solutions at finite temperature. We discuss the properties of the solutions and the interpretation in terms of holographic RG flows. |

**
Walking, weakly first-order phase transitions, and complex CFTs
**

Speaker: | Slava Rychkov |

Institution: | IHES, Bures-sur-Yvette and ENS, Paris |

Time: | Wednesday 6 March 2019, 15:15 |

Venue: | 2nd floor seminar room |

Abstract: | Most people have heard that the 2d Potts model with Q=5 states has a first order phase transition, but not everyone knows that the correlation length at this phase transition is 2500 lattice spacings. We will review "walking RG" behavior in gauge theories and connect it to Type II weak first-order phase transitions in statistical physics. Despite appearing in very different systems (QCD below the conformal window, the Potts model, deconfined criticality) these two phenomena both imply approximate scale invariance in a range of energies and have the same RG interpretation: a flow passing between pairs of fixed point at complex coupling, dubbed "complex CFTs". Observables of the real walking theory are approximately computable by perturbing the complex CFTs. The general mechanism will be illustrated by a specific and computable example: the two-dimensional Q-state Potts model with Q > 4. |

**
Renormalization Group and Conformal Bootstrap: Friends or Foes?
**

Speaker: | Slava Rychkov |

Institution: | IHES, Bures-sur-Yvette and ENS, Paris |

Time: | Thursday 7 March 2019, (Colloqium 17:00) |

Venue: | 3rd floor seminar room |

Abstract: | For almost 50 years Renormalization Group has been the workhorse of the theory of critical phenomena such as the liquid-gas critical point or the Curie temperature of a ferromagnet (Ising model). In the last 10 years a new method called the Conformal Bootstrap has been making significant progress. We will review the story of this friendly competition, and the main challenges faced by the two approaches. |

**
Making the Case for Nonlocal Modifications of Gravity
**

Speaker: | Richard Woodard |

Institution: | Florida University |

Time: | Tuesday 12 March 2019, at 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | TBA |

**
Exploring greek tumulus for hidden monuments with cosmic rays
**

Speaker: | Yannis Karyotakis |

Institution: | LAPP-IN2P3, CNRS, France |

Time: | Thursday 14 March 2019 (Colloqium 17:00) |

Venue: | 3rd floor Seminar Room |

Abstract: | Modern high energy physics experiments were initiated at the beginning of the 20th century, by experimental physicists searching to understand the ambient radioactivity and exploring particles arriving from the open sky. For many years the universe was the only source of high energy particles, and few fundamental discoveries were done, detecting cosmic particles. I will review one hundred years of observations, show some of the current experiments and comment on our present knowledge and problems. Finally I will show, how using cosmic muons we can explore the Macedonian funeral tumulus or the pyramids to detect hidden monuments or hidden rooms ! The colloquium is for a large public, not necessary familiar with particle physics. |

**
Bound states in dark matter phenomenology
**

Speaker: | Kalliopi Petraki |

Institution: | LPTHE, Sorbonne Paris & Nikhef, Amsterdam |

Time: | Wednesday 3 April 2019, 13:00 |

Venue: | 2nd floor seminar room |

Abstract: | In the most traditional dark matter scenarios, dark matter is hypothesised to possess only contact-type interactions. However, there is motivation to consider dark matter coupled to light or massless force carriers. I will discuss some of the intricacies that arise in these scenarios, with emphasis on non-perturbative effects, in particular the formation of bound states and their phenomenological implications. |

**
Dark matter: canonical paradigms and beyond
**

Speaker: | Kalliopi Petraki |

Institution: | LPTHE, Sorbonne Paris & Nikhef, Amsterdam |

Time: | Thursday 4 April 2019, (Colloqium 17:00) |

Venue: | 3rd floor seminar room |

Abstract: | Most of the matter in our universe is in the form of some yet unknown particles, known as dark matter. Besides providing firm evidence for the existence of unknown fundamental physics, dark matter is essential in understanding how our universe evolved to be the way we observe it today. The research of the past decades led to the development of two canonical paradigms for the properties of dark matter: the collisionless cold dark matter paradigm, supported by the observed gravitational clustering, and the WIMP paradigm, which provides a well-motivated particle physics framework for collisionless cold dark matter. However, current observational and experimental results motivate looking beyond these scenarios. I will review the canonical paradigms, discuss some of the motivation to move beyond them, and describe new directions and challenges in exploring the phenomenology of dark matter with different particle physics interactions than in the canonical scenario. |

**
Effective theory of large scale structure
**

Speaker: | Nikolaos Tetradis |

Institution: | University of Athens |

Time: | Monday 8 April 2019, 15:15 |

Venue: | 2nd floor seminar room |

Abstract: | I discuss the effective description of dark matter as a cosmological fluid at large scales. The focus is on the growth of cosmological perturbations, for which perturbation theory fails to converge. The effective approach employs the notion of coarse-graining and field-theoretical techniques. Dark matter is best described as a viscous fluid with nonzero sound velocity. |

**
Conformal anomalies, C-theorems and RG Flows I
**

Speaker: | Adam Schwimmer |

Institution: | Weizmann Institute of Science |

Time: | Tuesday 9 April 2019, 14:15 - 16:00 |

Venue: | 2nd floor seminar room |

Abstract: |
Contents of the mini-course:
-Generalities:Analyticity,Locality,Weyl transformations-Conformal Group -Classification and Structure of Weyl Anomalies.The Osborn(local Callan-Symanzik Equation). -Zamolodchikov Theorem in d=2. -Weyl Anomaly Matching and the a-theorem. Alternative arguments for a-theorem. -Weyl Anomalies in Holography, Anomalies and the Geometry of Moduli Space -More on the Structure of the Osborn Equation. |

**
Conformal anomalies, C-theorems and RG Flows II
**

Speaker: | Adam Schwimmer |

Institution: | Weizmann Institute of Science |

Time: | Wednesday 10 April 2019, 14:15 - 16:00 |

Venue: | 1rst floor seminar room |

Abstract: |
Contents of the mini-course:
-Generalities:Analyticity,Locality,Weyl transformations-Conformal Group -Classification and Structure of Weyl Anomalies.The Osborn(local Callan-Symanzik Equation). -Zamolodchikov Theorem in d=2. -Weyl Anomaly Matching and the a-theorem. Alternative arguments for a-theorem. -Weyl Anomalies in Holography, Anomalies and the Geometry of Moduli Space -More on the Structure of the Osborn Equation. |

**
Conformal anomalies, C-theorems and RG Flows III
**

Speaker: | Adam Schwimmer |

Institution: | Weizmann Institute of Science |

Time: | Thursday 11 April 2019, 13:15 - 15:00 |

Venue: | 1rst floor seminar room |

Abstract: |
Contents of the mini-course:
-Generalities:Analyticity,Locality,Weyl transformations-Conformal Group -Classification and Structure of Weyl Anomalies.The Osborn(local Callan-Symanzik Equation). -Zamolodchikov Theorem in d=2. -Weyl Anomaly Matching and the a-theorem. Alternative arguments for a-theorem. -Weyl Anomalies in Holography, Anomalies and the Geometry of Moduli Space -More on the Structure of the Osborn Equation. |

**
The gravitational-wave astronomy: from the first results to the scientific potential of next data takings
**

Speaker: | Matteo Barsuglia |

Institution: | Institute Fresnel, APC, CNRS, France |

Time: | Thursday 11 April 2019, 17:00 |

Venue: | 3rd floor seminar room (Colloqium Series) |

Abstract: | On September 15th 2015, the two LIGO interferometers detected the first gravitational-wave, produced by the merger of two black-holes. On August 17th 2017, the coalescence of two neutron stars, localized by the network LIGO-Virgo, allowed the most important multi-messenger observation campaign of the history. Among the main results of this new gravitational-wave astronomy: the demonstration that binary black-holes exist and they can merge, the discovery of a new population of stellar mass black-holes, the link between short gamma-ray burst and mergers of neutron stars, a new measurement of the Hubble constant, the measurement of the gravitational-wave speed and the measurement of the deformability of neutron stars. After a summary of the results obtained so far, I will describe the observational plans of the next years and the challenges associated with the improvements of the gravitational-wave detectors. I will focus the last part of this seminar on the scientific potential of the new data takings, for the astrophysics of compact objects, for the cosmology and for the tests of gravity. |

**
Meta-stable non-extremal anti-branes
**

Speaker: | Vasilis Niarchos |

Institution: | Durham University |

Time: | Tuesday 16 April 2019, 15:00 |

Venue: | 2nd floor seminar room |

Abstract: | We analyse anti-D3 branes at the tip of the Klebanov-Strassler (KS) throat using the blackfold formalism. This enables us to study how temperature affects the conjectured meta-stable state. In the extremal limit we recover the results of Kachru, Pearson and Verlinde (KPV). Away from extremality we find a meta-stable black NS5 state that disappears near a geometric transition where black anti-D3 branes and black NS5 branes become indistinguishable. This is consistent with earlier results based on regularity conditions of backreacted solutions and provides non-trivial evidence for the meta-stability of anti-branes in non-compact throat geometries. |

**
Cosmic Rays and Gamma-Ray Bursts
**

Speaker: | Alvaro de Rujula |

Institution: | CERN & IFT, Madrid |

Time: | Thursday 18 April 2019, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | There has been considerable recent progress in the measurements of primary cosmic rays (electrons and nuclei), as well as in the detection of the gamma rays and the lower-energy ``afterglow" associated with the binary neutron-star merger that was first seen by the gravitational wave detectors. I shall discuss these results and some of their interpretation(s). |

**
Einstein's errors, triumphs and misconceptions
**

Speaker: | Alvaro de Rujula |

Institution: | CERN & IFT, Madrid |

Time: | Thursday 18 April 2019, 17:00 (Colloqium series) |

Venue: | 3rd floor seminar room |

Abstract: | Coinciding with the centenaries of special and general relativity (in 2005 and 2016) there were innumerable celebrations and discussions of Einstein's unique genius and contributions. But Uncle Albert was also human, and managed to be misleading or plainly wrong on many occasions. It may be interesting to discuss the errors of his ways, interspaced with various old or very recent observational proofs of how precisely right he often was. |

**
Baryons from homogeneous fields in holographic QCD
**

Speaker: | Matti Jarvinen |

Institution: | Utrecht University |

Time: | Thursday 2 May 2019, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | Baryons can be included as solitonic "instanton" configurations of gauge fields in large-Nc holographic models for QCD. Dense baryonic matter is then modeled by tightly packed soliton lattices which are hard to analyze analytically and numerically. Approximating such configurations by using homogeneous gauge fields may however capture the most important features. I discuss this approach for holographic models of QCD in the Veneziano limit (V-QCD). I demonstrate that homogeneous holographic baryons lead to a reasonable phase diagram and lead to a stiff equation of state (EoS) for the baryons with the speed of sound well above the conformal value. Consequently one can construct a hybrid EoS as a combination with holographic EoSs for the baryons and quark matter with a low density nuclear matter EoS which passes all constraints from observations of neutron stars and their mergers. |

**
Strong cosmic censorship (in de Sitter backgrounds)
**

Speaker: | Oscar J. Dias |

Institution: | University of Southampton |

Time: | Thursday 9 May 2019, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | Generically, strong cosmic censorship (SCC) is the statement that physics within general relativity should be predicted from initial data prescribed on an initial hypersurface. In this talk I will review how fine-tuned versions of SCC have been formulated along the last decades up to the point where we believe that Christodoulou's version is true in asymptotically flat spacetimes. However, I will also describe that in the last 2 years it was found that this is no longer necessarily true for some de Sitter backgrounds. |

**
Localised thermal phases in holography
**

Speaker: | Oscar J. Dias |

Institution: | University of Southampton |

Time: | Friday 10 May 2019, 11:15 |

Venue: | 2nd floor seminar room |

Abstract: | Within the gauge/gravity correspondence, black holes are dual to CFT thermal states. I will discuss asymptotically global AdS_5 x S^5 black holes that are localised on the S^5. These are solutions of type IIB supergravity with S^8 horizon topology that dominate the theory in the microcanonical ensemble at small energies. At higher energies, there is a first-order phase transition to AdS_5-Schwarzschild x S^5. By the AdS/CFT correspondence, this transition is dual to spontaneously breaking the SO(6) R-symmetry of N = 4 super Yang-Mills down to SO(5). I will also discuss localised and nonuniform thermal states of super-Yang-Mills on a circle at strong coupling and associated phase transitions that are reproduced by lattice computations. |

**
The Calogero model: physics, mathematics and recent results
**

Speaker: | Alexios Polychronakos |

Institution: | The City College of New York |

Time: | Monday 1 July 2019, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | A review of the Calogero integrable model and its various generalizations will be given, with emphasis on mathematical properties and recent results. Topics will include integrability, the connection with fractional statistics, their matrix model and operator formulations, their various reductions and extensions, and their hydrodynamic description, properties and solitons. |

**
Weyl Symmetry in Gravity
**

Speaker: | Tomislav Prokopec |

Institution: | University of Utrecht |

Time: | Tuesday 2 July 2019, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | I will discuss prospects of formulating simple extensions of the standard model and gravity that exhibit local Weyl symmetry in the ultraviolet. The principal advantage of such constructions is that they naturally address the gauge and gravitational hierarchy problem. Furthermore, I will argue that Cartan-Einstein gravity provides a natural framework for conformal symmetry, as this theory contains torsion vector which can be interpreted as the Weyl vector. I will also discuss other potential observable consequences of conformal symmetry arising from electroweak symmetry breaking and cosmic inflation. |