Speakers
Pascal Anastasopoulos: Light stringy states and the Yukawas
We investigate light massive string states that appear at brane intersections. They replicate the massless spectrum in a richer fashion and may be parametrically lighter than standard Regge excitations.We compute tri-linear Yukawa couplings of such open-string states to massless ones and to one another. Due to ambiguities in the normalisation of the vertex operators, that involve twist fields, we proceed via factorization of appropriate scattering amplitudes. Some peculiar features are observed that may lead to interesting signatures at colliders in the future.
Christos Charmousis: Self Tuning the cosmological constant
We will briefly discuss the cosmological dark energy problem and efforts towards solving it using self tuning ideas. We will discuss in particular a self tuning model originating from a braneworld holographic model. I will explain briefly constraints from recent neutron binary observations on 4 dimensional scalar tensor theories of modified gravity.
Ilias Cholis: Dark Matter and Gravitational Waves
Last year the first detection of gravitational waves was announced by LIGO, opening a new window to study the cosmos. Of the many questions we can ask, I am going to focus on the one pertaining to the nature of dark matter. In my talk, I am going to show that if dark matter is composed of primordial black holes produced at the early stages of the Universe, with a characteristic mass range of 10-100 solar masses; then the LIGO interferometers can be used to indirectly detect dark matter in the local Universe. Furthermore I am going to discus probes to use and the possible signals to search for in order to achieve that goal.
Anastasia Doikou: On quantum Darboux-Bäcklund transformations
We discuss the notion of the quantum auxiliary linear problem and the associated problem of quantum Darboux-Bäcklund transformation. In this frame we derive the analogue of the classical formula that provides the hierarchy of the time components of Lax pairs at the quantum level for both closed and open integrable lattice models. The generic time evolution operator formula is particularly interesting and novel at the quantum level when dealing with systems with open boundary conditions. Particular emphasis is given to the time part of the quantum transformation as possible connections and applications to the problem of quantum quenches as well as the time evolution of local quantum impurities are evident. A discussion on the use of Bethe states as well as coherent states for the study of the time evolution is also presented.
Theodora Ioannidou: Sprinors, Strings and Integrable Systems
This talk deals with various interrelations between strings and surfaces in three dimensional ambient space, two dimensional integrable models. Initially, a spinor version of the Frenet equation is introduced in order to describe the differential geometry of static three dimensional string-like structures. Finally, its extension to discrete space is going to be presented.
Georgios Itsios: Mesonic excitations in (non-)Abelian T-dual backgrounds
In this talk I will describe the mesonic excitations of a D6 brane that probes the non-Abelian T-dual version of the well known type IIB solution with geometry AdS5 x S5. A comparison of the spectra before and after the non-Abelian T-duality transformation reveals several interesting differences which I will try to interpret. At the end of the talk I will also discuss the case of the Abelian T-duality.
Motivated by work in nonlinear optics, as well as more recently in Bose-Einstein condensate mixtures, we will explore a series of nonlinear states that arise in such systems. We will start from a single structure, the so-called dark-bright solitary wave, and then expand our considerations to multiple such waves, their spectral properties, nonlinear interactions and experimental observations. A twist will be to consider the dark solitons of the one component as effective potentials that will trap the bright waves of the second component, an approach that will also prove useful in characterizing the bifurcations and instabilities of the system. Beating so-called dark-dark soliton variants of such states will also be touched upon. Generalizations of all these notions in higher dimensions and, so-called, vortex-bright solitons will also be offered. Connections to particle physics, including with topological particles such as skyrmions, hopfions and merons, as well as challenges for future work will be discussed.
Elias Kiritsis: Exotic holographic RG flows and quantum phase transitions
Holographic RG flows are studied in an Einstein-dilaton theory with a general potential. Novel solutions are found that have exotic properties from a RG point-of view. Some have β-functions that are defined patch-wise and lead to flows where the β-function changes sign without the flow stopping. Others describe flows that end in non-neighboring extrema in field space. Finally others describe regular flows between two minima of the potential and correspond holographically to flows driven by the VEV of an irrelevant operator in the UV CFT. we then consider holographic RG flows dual to QFTs on maximally symmetric curved manifolds (dSd, AdSd, and S^d) SThe general properties of such flows are analyzed and the UV and IR asymptotics computed. New RG flows can appear at finite curvature which do not have a zero curvature counterpart. The so-called 'bouncing flows', where the β-function has a branch cut at which it changes sign, are found to persist at finite curvature. Novel quantum first-order phase transitions are found, triggered by a variation in the d-dimensional curvature in theories allowing multiple ground states.
Chris Kouvaris: Probing Light Dark Matter
Today, there are strong indications pointing on the existence of dark matter. I will claim that dark matter plays a key role both in particle physics and cosmology and I will review the status of dark matter direct detection experiments. Furthermore I will argue that newly proposed theoretical techniques can facilitate the experimental searches of dark matter in the sub-GeV mass region, opening a whole new dark matter parameter space to direct detection experiments.
Costis Papageorgakis: Deconstructing the BPS Sector of the 6D (2,0) Theory
I will introduce the (2,0) superconformal field theory in 6D, some of its features and various avenues towards its study. I will then focus on the "deconstruction" proposal and a recent, related calculation that reproduces the exact BPS partition function of the (2,0) theory on a torus.
Anastasios Petkou: Modern CFT in d>2: some recent results
After a brief review of the modern approach to CFTs in d>2, I will discuss how the theory space near generalised free CFTs in any dimension can be drawn using the analytic structure of the conformal OPE.
Achilleas Porfyriadis: Observational implications of Kerr/CFT
I will review recent work on observational implications of the Kerr/CFT correspondence for astrophysically relevant black holes in the sky. Near extremality, conformal symmetry in the near-horizon region implies a variety of qualitatively new and potentially observable signals in the gravitational wave and optical windows. I will present explicit analytical gravitational waveforms for extreme-mass-ratio-inspirals in the near-horizon region of near-extreme Kerr black holes. I will also explain how one finds analytically the null geodesics which extend from the near-horizon region out to a distant observatory and how one uses them to do geometric optics in order to compute electromagnetic emission profiles from the innermost part of an accretion disc.
Evangelos Sfakianakis: Higgsed Gauge-flation and beyond: Inflation with Non-abelian Gauge Fields
I will introduce a class of inflationary models, where inflation is driven exclusively or in part by non-abelian gauge fields. I will describe how the spectrum of density fluctuations and gravitational waves is computed, and show that these models can produce observationally viable spectra, if the gauge symmetry is spontaneously broken by a Higgs sector. The background gauge field texture violates parity, resulting in a chiral gravitational wave spectrum. This arises due to an exponential enhancement of one polarization of the spin-2 fluctuation of the gauge field. Higgsed Gauge-flation and related models can produce observable gravitational waves at inflationary energy scales well below the GUT scale.
Thomas Sotiriou: No-hair theorems and hairy black holes
I will discuss no-hair theorems for scalar fields. I will argue that part of their value lies in clearly identifying the assumptions that one needs to violate in order to have black holes that differ from those of General Relativity. I will then briefly review some hairy black hole scenarios and comment of the prospects of detecting black hole hair with gravitational wave observations.