### University of Crete HEP Seminars: Fall 2015

**
Algebraically special spacetimes and holography
**

Speaker: | Ayan Mukhopadhyay |

Institution: | University of Crete |

Time: | Tuesday 29 September 2015, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | Algebraically special asymptotically AdS spacetimes have the distinct characteristic that the boundary metric and the dual stress tensor are related locally independent of the initial conditions. We will show that this relation can be captured by a complex symmetric traceless and conserved tensor, whose form is related to the Petrov classification of the bulk spacetime. This holographic point of view allows us to get immense wealth of information about multi-point thermal correlation functions of the stress-tensor in the dual field theory. We will show that an infinite number of hydrodynamic transport coefficients of a special type should vanish in such field theories. We can also extract similar information about correlation functions even far beyond the hydrodynamic regime. |

**
Holographic competition of phases and superconductivity
**

Speaker: | Li Li |

Institution: | University of Crete |

Time: | Tuesday 6 October 2015, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | We use a holographic theory to model and study the competition of four phases: an antiferromagnetic phase, a superconducting phase, a metallic phase and a striped phase, using as control parameters temperature and a doping-like parameter. We analyse the various instabilities and determine the possible phases. One class of phase diagrams, that we analyse in detail, is similar to that of high-temperature superconductors as well as other strange metal materials. |

**
Hyperscaling-violating Lifshitz hydrodynamics from black holes
**

Speaker: | Yoshinori Matsuo |

Institution: | University of Crete |

Time: | Thursday 8 October 2015, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | Non-equilibrium black hole horizons are considered in scaling theories with generic Lifshitz invariance and an unbroken U(1) symmetry. There is also a special form of hyperscaling violation associated with a non-trivial conduction exponent. The boundary stress tensor is computed and renormalized and the associated hydrodynamic equations derived. Upon a non-trivial redefinition of boundary sources associated with the U(1) gauge field, the equations are mapped to the standard non-relativistic hydrodynamics equations coupled to a mass current and an external Newton potential in accordance with the general theory of [arXiv:1502.00228]. The shear viscosity to entropy ratio is the same as in the relativistic case. |

**
Gravitational back-reaction in cosmology
**

Speaker: | Nicholas Tsamis |

Institution: | University of Crete |

Time: | Tuesday 13 October 2015, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | We present some results from classical and quantum gravity in the presence of a positive cosmological constant that have interesting implications for early cosmology. |

**
Co-dimension-1 defects in Chern-Simons-matter theories
**

Speaker: | Vasilis Niarchos |

Institution: | University of Crete |

Time: | Tuesday 20 October 2015, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | I will discuss a recent formulation of bulk-boundary theories for domain walls and boundaries in three-dimensional Chern-Simons-matter theories. Special emphasis will be given to half-BPS defects in supersymmetric setups and the embedding of these results in string/M-theory. In M-theory I will present a proposal for the IR theory that resides at the (1+1)-dimensional M2-M5 intersection. |

**
Unifying ghost-free Lorentz-invariant Lagrangians
**

Speaker: | Wenliang Li |

Institution: | University of Crete |

Time: | Thursday 22 October 2015, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | We will present a novel unifying framework for Lorentz-invariant Lagrangian field theories that lead to second order equations of motion. The key ingredient is antisymmetry. Then we reformulate the general ghost-free Lagrangians in the language of differential forms. The absence of higher order equations of motion has a geometric nature. A new duality is proposed which generalizes the Hodge duality in Maxwellâ€™s theory. All well-known ghost-free Lagrangian theories for spin-0, spin-1, p-form, spin-2 fields have natural formulations in this framework. We will present many new ghost-free Lagrangians. The most interesting examples are novel nonlinear kinetic terms for the graviton, which will be discussed in more detail. |

**
Discrete symmetries from hidden sectors
**

Speaker: | Pascal Anastasopoulos |

Institution: | TU Wien |

Time: | Tuesday 27 October 2015, 15:00 |

Venue: | 2nd floor seminar room |

Abstract: | We study the presence of abelian discrete symmetries in globally consistent orientifold compactifications based on rational conformal field theory. We extend previous work by allowing the discrete symmetries to be a linear combination of U(1) gauge factors of the visible as well as the hidden sector. This more general ansatz significantly increases the probability of finding a discrete symmetry in the low energy effective action. Applied to globally consistent MSSM-like Gepner constructions we find multiple models that allow for matter parity or Baryon triality. |

**
Heavy-ion physics at LHC; current status and open questions
**

Speaker: | Panagiota Foka |

Institution: | GSI Helmholtz Centre for Heavy Ion Research, Darmstadt |

Time: | Thursday 29 October 2015, 15:00 |

Venue: | 2nd floor seminar room |

Abstract: | A new era in the study of high-energy nuclear collisions began when the CERN LHC provided the first collisions of lead nuclei in late 2010. In the first three years of operation the ALICE, ATLAS and CMS experiments collected Pb-Pb collision data exceeding any previously studied collision energies by more than an order of magnitude. These data have provided new insights into the properties of QCD matter under extreme conditions, with extensive measurements of soft particle production and newly accessible hard probes of the created hot and dense medium. An integral part of the heavy-ion program is the study of benchmark reference data provided by pp and pPb collisions. In this talk a comprehensive overview of the obtained results is provided. While the basic properties of the created medium were established at RHIC, the LHC data suggest many new avenues for extracting its properties in detail. The current status and open questions are outlined, in particular in understanding surprising results related to the reference systems. |

**
Behind the horizon in AdS/CFT
**

Speaker: | Kyriakos Papadodimas |

Institution: | CERN/University of Groningen |

Time: | Tuesday 10 November 2015, 15:00 |

Venue: | 2nd floor seminar room |

Abstract: | We discuss black hole information in the context of the AdS/CFT correspondence. |

**
Aspects of de Sitter spacetimes. Lecture 1
**

Speaker: | Dionysios Anninos |

Institution: | Institute for Advanced Study, Princeton |

Time: | Thursday 12 November 2015, 11:05 |

Venue: | 2nd floor seminar room |

Abstract: |
Classical de Sitter physics; small quantum fluctuations in de Sitter; semiclassical methods and the Wheeler—DeWitt equation; higher-spin de Sitter holography; and if time permits some aspects of holography in the static patch of de Sitter.
Some useful references are: hep-th/0110007 1205.3855 astro-ph/0210603 1406.5490 1007.0435 1108.5735 |

**
Aspects of de Sitter spacetimes. Lecture 2
**

Speaker: | Dionysios Anninos |

Institution: | Institute for Advanced Study, Princeton |

Time: | Monday 16 November 2015, 14:45 |

Venue: | 2nd floor seminar room |

Abstract: |
Classical de Sitter physics; small quantum fluctuations in de Sitter; semiclassical methods and the Wheeler—DeWitt equation; higher-spin de Sitter holography; and if time permits some aspects of holography in the static patch of de Sitter.
Some useful references are: hep-th/0110007 1205.3855 astro-ph/0210603 1406.5490 1007.0435 1108.5735 |

**
Aspects of de Sitter spacetimes. Lecture 3
**

Speaker: | Dionysios Anninos |

Institution: | Institute for Advanced Study, Princeton |

Time: | Tuesday 17 November 2015, 15:00 |

Venue: | 2nd floor seminar room |

Abstract: |
Classical de Sitter physics; small quantum fluctuations in de Sitter; semiclassical methods and the Wheeler—DeWitt equation; higher-spin de Sitter holography; and if time permits some aspects of holography in the static patch of de Sitter.
Some useful references are: hep-th/0110007 1205.3855 astro-ph/0210603 1406.5490 1007.0435 1108.5735 |

**
Aspects of de Sitter spacetimes. Lecture 4
**

Speaker: | Dionysios Anninos |

Institution: | Institute for Advanced Study, Princeton |

Time: | Wednesday November 18 2015, 14:00 |

Venue: | 2nd floor seminar room |

Abstract: |
Classical de Sitter physics; small quantum fluctuations in de Sitter; semiclassical methods and the Wheeler—DeWitt equation; higher-spin de Sitter holography; and if time permits some aspects of holography in the static patch of de Sitter.
Some useful references are: hep-th/0110007 1205.3855 astro-ph/0210603 1406.5490 1007.0435 1108.5735 |

**
Aspects of de Sitter spacetimes. Lecture 5
**

Speaker: | Dionysios Anninos |

Institution: | Institute for Advanced Study, Princeton |

Time: | Wednesday November 18 2015, 16:15 |

Venue: | 2nd floor seminar room |

Abstract: |
Classical de Sitter physics; small quantum fluctuations in de Sitter; semiclassical methods and the Wheeler—DeWitt equation; higher-spin de Sitter holography; and if time permits some aspects of holography in the static patch of de Sitter.
Some useful references are: hep-th/0110007 1205.3855 astro-ph/0210603 1406.5490 1007.0435 1108.5735 |

**
Aspects of de Sitter spacetimes. Lecture 6
**

Speaker: | Dionysios Anninos |

Institution: | Institute for Advanced Study, Princeton |

Time: | Thursday 19 November 2015, 14:30 |

Venue: | 3rd floor seminar room |

Abstract: |
Classical de Sitter physics; small quantum fluctuations in de Sitter; semiclassical methods and the Wheeler—DeWitt equation; higher-spin de Sitter holography; and if time permits some aspects of holography in the static patch of de Sitter.
Some useful references are: hep-th/0110007 1205.3855 astro-ph/0210603 1406.5490 1007.0435 1108.5735 |

**
Aspects of de Sitter spacetimes. Lecture 4
**

Speaker: | Dionysios Anninos |

Institution: | Institute for Advanced Study, Princeton |

Time: | Wednesday November 18 2015, 14:00 |

Venue: | 2nd floor seminar room |

Abstract: |
Classical de Sitter physics; small quantum fluctuations in de Sitter; semiclassical methods and the Wheeler—DeWitt equation; higher-spin de Sitter holography; and if time permits some aspects of holography in the static patch of de Sitter.
Some useful references are: hep-th/0110007 1205.3855 astro-ph/0210603 1406.5490 1007.0435 1108.5735 |

**
Aspects of de Sitter spacetimes. Lecture 5
**

Speaker: | Dionysios Anninos |

Institution: | Institute for Advanced Study, Princeton |

Time: | Wednesday November 18 2015, 16:15 |

Venue: | 2nd floor seminar room |

Abstract: |
Classical de Sitter physics; small quantum fluctuations in de Sitter; semiclassical methods and the Wheeler—DeWitt equation; higher-spin de Sitter holography; and if time permits some aspects of holography in the static patch of de Sitter.
Some useful references are: hep-th/0110007 1205.3855 astro-ph/0210603 1406.5490 1007.0435 1108.5735 |

**
Aspects of de Sitter spacetimes. Lecture 6
**

Speaker: | Dionysios Anninos |

Institution: | Institute for Advanced Study, Princeton |

Time: | Thursday 19 November 2015, 14:30 |

Venue: | 3rd floor seminar room |

Abstract: |
Classical de Sitter physics; small quantum fluctuations in de Sitter; semiclassical methods and the Wheeler—DeWitt equation; higher-spin de Sitter holography; and if time permits some aspects of holography in the static patch of de Sitter.
Some useful references are: hep-th/0110007 1205.3855 astro-ph/0210603 1406.5490 1007.0435 1108.5735 |

**
Hidden symmetries of black holes
**

Speaker: | David Chow |

Institution: | University of Crete |

Time: | Tuesday 24 November 2015, 15:00 |

Venue: | 2nd floor seminar room |

Abstract: | Many special properties of the Kerr black hole follow from the existence of a Killing tensor. I will discuss generalizations to black holes in string theory, for which Killing tensors are modified by a torsion. Kaluza-Klein lifts to higher dimensions require an algebraic condition, satisfied by known examples, that has several different consequences. General results will be given, as well as explicit examples. |

**
Holographic RG flows and quantum effective action
**

Speaker: | Wenliang Li |

Institution: | University of Crete |

Time: | Tuesday 1 December 2015, 15:00 |

Venue: | 2nd floor seminar room |

Abstract: | In gauge/gravity duality, the Einstein-scalar theory is dual to a boundary field theory minimally deformed by a scalar operator. We will present a novel formalism which is useful for the study of holographic RG flows and effective actions in the Einstein-scalar theory. The computation of the on-shell action and holographic renormalization are carried out explicitly. The renormalized generating functional at a finite energy scale is derived thanks to a set of new conserved quantities. As an application, the effective potential of a gluon condensate is computed. |

**
Effective holographic theories of thermoelectric transport
**

Speaker: | Blaise Goutéraux |

Institution: | Stanford University/APC, Université Paris Diderot-Paris 7 |

Time: | Tuesday 8 December 2015, 15:00 |

Venue: | 2nd floor seminar room |

Abstract: | In this talk, I will summarize recent progress in the description of thermoelectric transport using gauge/gravity duality. I will first review thermoelectric transport in hydrodynamics, where momentum conservation implies infinite zero-frequency conductivities. By a change of basis of the conserved currents, a universal, finite conductivity can be extracted. It can be computed holographically. I will discuss its low-temperature scaling in terms of critical exponents characterizing time and space anisotropy and anomalous dimensions for the free energy and conserved current. When momentum is almost conserved, the zero-frequency delta functions broaden into Drude-like peaks. A holographic computation precisely identifies the redistribution of the low-frequency spectral weight between two contributions originating from the non-conservation of momentum and intrinsic dissipation respectively. |

**
Informal discussion of "Effective field theory of dissipative fluids"
**

Speaker: | Wenliang Li |

Institution: | University of Crete |

Time: | Thursday 10 December 2015, 15:00 |

Venue: | 2nd floor seminar room |

Abstract: |
Brief, informal discussion of "Effective field theory of dissipative fluids," 1511.03646. |