Speakers

Tassos Vladikas: Standard Model Phenomenology (and beyond?) from Lattice QCD: A Homage to Giannis Bakas

Lattice QCD provides high-precision results for low energy strong interaction effects, essential to the study of flavour-phenomenological aspects of the Standard Model. We present world averages for a sample of quantities which provide stringent tests of the Standard Model (and possibly bounds for Physics beyond it).

Konstantinos Dimopoulos: Axionic Dark Energy in AGNs

AGN jets carry helical magnetic fields, which can affect dark matter if the latter is axionic. This preliminary study shows that, in the presence of strong helical magnetic fields, the nature of the axionic condensate may change and become dark energy. Being gravitationally repulsive, such dark energy may affect galaxy formation and galactic dynamics, so this possibility should not be ignored when considering axionic dark matter.

Asimina Arvanitaki: Unraveling the Mystery of Dark Matter

Dark Matter constitutes a significant component of the energy budget of our Universe and we have diagnosed its existence through its gravitational interaction with us. Our theories of Dark Matter though predict that this glue that is responsible for the existence of our Galaxy should also interact with us in non-trivial ways. After I review these ideas, I will discuss how we can learn more about the properties of Dark Matter in a variety of new experiments, ranging from atomic clocks to black holes and gravitational waves.

Evangelos Sfakianakis: From axion inflation to leptons, baryons and cosmological magnetic fields.

Axions are attractive candidates for theories of large-field inflation that are capable of generating observable primordial gravitational wave backgrounds. These fields enjoy shift-symmetries that protect their role as inflatons from being spoiled by coupling to unknown UV physics. This symmetry also restricts the couplings of these axion fields to other matter fields. At lowest order, the only allowed interactions are derivative couplings to gauge fields and fermions. These derivative couplings lead to the biased production of fermion and gauge-boson helicity states during and after inflation. I will describe some recent work on preheating in axion-inflation models that are derivatively coupled to Abelian gauge-fields and fermion axial-currents.

Andrei Parnachev: Constraints in unitary conformal field theories

We will describe constraints on the three-point functions of operators with spin which follow from conformal symmetry and unitarity. We will also discuss implications for the AdS/CFT correspondence.

Panos Betzios: Matrix Quantum Mechanics on the S^1/Z_2 orbifold

We revisit c=1 non-critical string theory and its formulation via Matrix Quantum Mechanics (MQM). In particular we study the theory on an S^1/Z_2 orbifold of Euclidean time and try to compute its partition function in the grand canonical ensemble that allows one to study the double scaling limit of the matrix model and connect the result to string theory (Liouville theory). En route, we take advantage of some beautiful mathematics related to Fredholm Pfaffians and Elliptic functions. We also compare the partition function with the cases of the circle and the Euclidean 2d black hole. Finally, we will make some comments regarding the possibility of using this model as a toy model of a two dimensional big-bang big-crunch universe.

Nikos E. Mavromatos: CPT Violation in the (string-inspired) Early Universe, Neutrinos and the Matter Antimatter asymmetry

I discuss a string-inspired model of the early Universe, in which heavy right handed Majorana neutrinos propagating in the background of a four-dimensional Kalb-Ramond antisymmetric tensor can be responsible for generating a CP- and CPT-violating Lepton asymmetry already at tree level in perturbation theory, in contrast to the conventional CP violating but CPT conserving case. The Lepton asymmetry is then communicated to the baryon sector via Baryon-Lepton (B-L) number conserving processes in the standard model sector. For seesaw-type mass generation for light (active) neutrinos, one needs at least two heavy right-handed neutrinos for phenomenological reasons. However, the above mechanism of matter-antimatter asymmetry generation can be realised even with a single flavour of massive right handed neutrinos. In the latter case, quantum fluctuations of the antisymmetric tensor field strength (which in four dimensional universes is equivalent to (the derivative of) a pseudoscalar field (Kalb-Ramond axion)) may provide, upon kinetic mixing of the Kalb-Ramond axion with ordinary axions and breaking of the shift symmetry via appropriate Yukawa couplings of the ordinary axion fields with the active neutrinos, a mechanism for generation of Majorana masses for the light neutrinos beyond seesaw, which occurs at three loops. This latter mechanism is based on chiral gauge and gravitational anomalies.

Orestis Vasilakis: On the chiral ring of warped AdS(3)

I will be presenting results on the KK spectrum of warped AdS(3) compactifications of type IIB supergravity with five-form flux, which are dual to (0,2) SCFTs in two dimensions. We will see that a subset of the chiral ring of the dual field theories corresponds to holomorphic functions on the internal manifold. As an example we will consider geometries dual to the twisted compactification of four dimensional Y^{p,q} SCFTs on a Riemann surface for the case of the universal twist.

Constantia Alexandrou: Highlights of recent lattice QCD results

Ab initio simulation of the theory of the strong interactions, Quantum Chromodynamics (QCD), has advanced tremendously. We will review the status of state-of-the-art simulations and present selective results that attest to this progress. In particular, we will discuss results on the nucleon quark content and their relevance to dark matter searches, on the spin carried by quarks in the nucleon in relation to the long-standing puzzle of the nucleon spin, and the neutron electric dipole moment for probing physics beyond the standard model.

Praxitelis Ntokos: Generalized geometric vacua with 8 supercharges

We investigate compactifications of type II and M-theory down to AdS5 with generic fluxes that preserve eight supercharges, in the framework of Exceptional Generalized Geometry. The geometric data and gauge fields on the internal manifold are encoded in a pair of generalized structures corresponding to the vector and hyper-multiplets of the reduced five-dimensional supergravity. Supersymmetry translates into integrability conditions for these structures, generalizing, in the case of type IIB, the Sasaki-Einstein conditions. We show that the ten and eleven-dimensional type IIB and M-theory Killing-spinor equations specialized to a warped AdS5 background imply the generalized integrability conditions. I will also comment on possible applications to AdS/CFT.

Phivos Mavropoulos: Topological Insulators: Time-reversal symmetry, spin scattering, and quasiparticle interference spectra

Topological insulators is a new class of materials where the topology of the electron band structure, influenced by strong spin-orbit coupling and breaking of space-inversion symmetry, induces robust surface states characterized by a spin-momentum locking. Time-reversal symmetry prohibits back-scattering events in these states with profound consequences in charge- and spin-transport phenomena. However, magnetic defects at the surface break the time-reversal symmetry, opening the back-scattering channel. This in turn appears as a quasiparticle interference wave pattern when measured by means of scanning tunneling microscopy. Appropriate doping shapes the Fermi surface into a hexagonal form, in which nested Fermi wave-vectors cause a focusing effect with directional standing waves of large coherence length. In a combined experimental and theoretical effort, these phenomena are investigated on the surface of the strong topological insulator Bi 2 Te 3.

Olga Papadoulaki: A magnetically induced quantum critical point in holography

We are using holography to study quantum phase transitions in a 2+1 D strongly coupled non conformal gauge theory at finite chemical potential and magnetic field B. Our gravity dual is 4D N = 2 Fayet-Iliopoulos gauged supergravity. We found a line of quantum critical points at B=Bc between extremal dyonic black branes and extremal magnetically charged "thermal gas" solutions. We will introduce the two types of solutions, their thermodynamics and their phase diagram. Then we will discuss the physics of the critical point and we will point out qualitative similarities between our field theory and Nambu- Jona- Lasinio model in 2+1 D under the presence of an external magnetic field. We will conclude with some open questions both on the gravity and field theory side and we will discuss future directions.