arXiv subjects

Elias Kiritsis

Publications and source records attributed to Elias Kiritsis.

At least 73 records · Page 4Linked to original sources

arXiv2015

Schroedinger Invariance from Lifshitz Isometries in Holography and Field Theory

We study non-relativistic field theory coupled to a torsional Newton-Cartan geometry both directly as well as holographically. The latter involves gravity on asymptotically locally Lifshitz space-times. We define an energy-momentum tensor and a mass current and study the relation between conserved currents and conformal Killing vectors for flat Newton-Cartan backgrounds. It is shown that flat NC space-time realizes two copies of the Lifshitz algebra that together form a Schroedinger algebra (without the central element). We show why the Schroedinger scalar model has both copies as symmetries and the Lifshitz scalar model only one. Finally we discuss the holographic dual of this phenomenon by showing that the bulk Lifshitz space-time realizes the same two copies of the Lifshitz algebra.

hep-th↗

arXiv2015

Field Theory on Newton-Cartan Backgrounds and Symmetries of the Lifshitz Vacuum

Holography for Lifshitz space-times corresponds to dual field theories on a fixed torsional Newton-Cartan (TNC) background. We examine the coupling of non-relativistic field theories to TNC backgrounds and uncover a novel mechanism by which a global U(1) can become local. This involves the TNC vector $M_μ$ which sources a particle number current, and which for flat NC space-time satisfies $M_μ=\partial_μM$ with a Schroedinger symmetry realized on $M$. We discuss various toy model field theories on flat NC space-time for which the new mechanism leads to extra global space-time symmetries beyond the generic Lifshitz symmetry, allowing for an enhancement to Schroedinger symmetry. On the holographic side, the source $M$ also appears in the Lifshitz vacuum with exactly the same properties as for flat NC space-time. In particular, the bulk diffeomorphisms that preserve the boundary conditions realize a Schroedinger algebra on $M$, allowing for a conserved particle number current. Finally, we present a probe action for a complex scalar field on the Lifshitz vacuum, which exhibits Schroedinger invariance in the same manner as seen in the field theory models.

hep-th↗

arXiv2014

On the gluon operator effective potential in holographic Yang-Mills theory

The holographic formalism is applied to the calculation of the effective potential for the scalar glueball operator. Three different versions of this operator are defined, and for each we compute the associated effective potential and discuss its properties and scheme ambiguities. Contact is made to earlier attempts to guess this effective potential from the conformal anomaly. We apply our results to the Improved Holographic QCD model calculating the glueball condensate.

hep-th↗

arXiv2014

Holographic Metals and Insulators with Helical Symmetry

Homogeneous, zero temperature scaling solutions with Bianchi VII spatial geometry are constructed in Einstein-Maxwell-Dilaton theory. They correspond to quantum critical saddle points with helical symmetry at finite density. Assuming $AdS_{5}$ UV asymptotics, the small frequency/(temperature) dependence of the AC/(DC) electric conductivity along the director of the helix are computed. A large class of insulating and conducting anisotropic phases is found, as well as isotropic, metallic phases. Conduction can be dominated by dissipation due to weak breaking of translation symmetry or by a quantum critical current.

hep-th↗

arXiv2014

Gravity and axions from a random UV QFT

It is postulated that the UV QFT is enormous and random. The coupling of the Standard Model to such QFT is analyzed. It is argued that massless 4d gravity and axions are general avatars of the postulate. The equivalence principle emerges naturally as well as a concrete set of sources for its breaking. The axion scale is related to the 4d Planck scale as $f=M_P/N$, where $N$ is the "number of colors" of the (almost) hidden UV CFT.

hep-ph↗

arXiv2014

Gravitational collapse and thermalization in the hard wall model

We study a simple example of holographic thermalization in a confining field theory: the homogeneous injection of energy in the hard wall model. Working in an amplitude expansion, we find black brane formation for sufficiently fast energy injection and a scattering wave solution for sufficiently slow injection. We comment on our expectations for more sophisticated holographic QCD models.

hep-th↗

arXiv2014

Holographic RG flow and the Quantum Effective Action

The calculation of the full (renormalized) holographic action is undertaken in general Einstein-scalar theories. The appropriate formalism is developed and the renormalized effective action is calculated up to two derivatives in the metric and scalar operators. The holographic RG equations involve Ricci flow for the space-time metric as well as the standard $β$-function flow for scalar operators. Several examples are analyzed and the effective action is calculated. A set of conserved quantities of the holographic flow is found, whose interpretation is not yet understood.

hep-th↗

arXiv2013

Holographic RG flows and nearly-marginal operators

The holographic renormalization group flows associated with marginally relevant operators are analyzed. The associated perturbative and non-perturbative beta-functions are calculated and the consistent scalar potentials are identified. The presence of a Zamolodchikov metric in the multiscalar case is shown to affect beta-functions starting at two loops.

hep-th↗

arXiv2013

The discontinuities of conformal transitions and mass spectra of V-QCD

Zero temperature spectra of mesons and glueballs are analyzed in a class of holographic bottom-up models for QCD in the Veneziano limit, N_c -> infinity, N_f -> infinity, with x = N_f/N_c fixed (V-QCD). The backreaction of flavor on color is fully included. It is found that spectra are discrete and gapped (modulo the pions) in the QCD regime, for x below the critical value x_c where the conformal transition takes place. The masses uniformly converge to zero in the walking region x -> x_c^- due to Miransky scaling. All the ratios of masses asymptote to non-zero constants as x -> x_c^- and therefore there is no "dilaton" in the spectrum. The S-parameter is computed and found to be of O(1) in units of N_f N_c in the walking regime, while it is always an increasing function of x. This indicates the presence of a subtle discontinuity of correlation functions across the conformal transition at x = x_c.

hep-ph↗

arXiv2013

Large-N limits of 2d CFTs, Quivers and AdS_3 duals

We explore the large-N limits of 2d CFTs, focusing mostly on WZW models and their cosets. The $SU(N)_k$ theory is parametrized in this limit by a 't Hooft-like coupling. We show a duality between strong coupling, where the theory is described by almost free fermions, and weak coupling where the theory is described by bosonic fields by an analysis of spectra and correlators. The AdS$_3$ dual is described, and several quantitative checks are performed. Besides the more standard states that should correspond to bulk black holes we find ground states with large degeneracy that can dominate the standard Cardy entropy at weak coupling and are expected to correspond to regular horizonless semiclassical bulk solutions.

hep-th↗

arXiv2013

The Chern-Simons Diffusion Rate in Improved Holographic QCD

In (3+1)-dimensional SU(Nc) Yang-Mills (YM) theory, the Chern-Simons diffusion rate, Gamma_{CS}, is determined by the zero-momentum, zero-frequency limit of the retarded two-point function of the CP-odd operator tr[F ^ F], with F the YM field strength. The Chern-Simons diffusion rate is a crucial ingredient for many CP-odd phenomena, including the chiral magnetic effect in the quark-gluon plasma. We compute Gamma_{CS} in the high-temperature, deconfined phase of Improved Holographic QCD, a refined holographic model for large-Nc YM theory. Our result for Gamma_{CS}/(sT), where s is entropy density and T is temperature, varies slowly at high T and increases monotonically as T approaches the transition temperature from above. We also study the retarded two-point function of tr[F ^ F] with non-zero frequency and momentum. Our results suggest that the CP-odd phenomena that may potentially occur in heavy ion collisions could be controlled by an excitation with energy on the order of the lightest axial glueball mass.

hep-th↗

arXiv2013

Asymptotic freedom, asymptotic flatness and cosmology

Holographic RG flows in some cases are known to be related to cosmological solutions. In this paper another example of such correspondence is provided. Holographic RG flows giving rise to asymptotically-free $β$-functions have been analyzed in connection with holographic models of QCD. They are shown upon Wick rotation to provide a large class of inflationary models with logarithmically-soft inflaton potentials. The scalar spectral index is universal and depends only on the number of e-foldings. The ratio of tensor to scalar power depends on the single extra real parameter that defines this class of models. The Starobinsky inflationary model as well as the recently proposed models of T-inflation are members of this class. The holographic setup gives a completely new (and contrasting) view to the stability, naturalness and other problems of such inflationary models.

hep-th↗

arXiv2013

On novel string theories from 4d gauge theories

We investigate strings theories as defined from four dimensional gauge theories. It is argued that novel (super)string theories exist up to 26 dimensions. Some of them may support weakly curved geometries.

hep-th↗

arXiv2012

V-QCD: Spectra, the dilaton and the S-parameter

Zero temperature spectra of mesons and glueballs are analyzed in a class of holographic bottom-up models for QCD (named V-QCD), as a function of x = N_f/N_c with the full back-reaction included. It is found that spectra are discrete and gapped (modulo the pions) in the QCD regime, for x below the critical value x_c where the conformal transition takes place. The masses uniformly converge to zero in the walking region x -> x_c due to Miransky scaling. The ratio of masses all asymptote to non-zero constants as x -> x_c and therefore there is no "dilaton" in the spectrum. The S-parameter is computed and found to be of O(1) in the walking regime.

hep-ph↗

arXiv2012

Lorentz violation, Gravity, Dissipation and Holography

We reconsider Lorentz Violation (LV) at the fundamental level. We show that Lorentz Violation is intimately connected with gravity and that LV couplings in QFT must always be fields in a gravitational sector. Diffeomorphism invariance must be intact and the LV couplings transform as tensors under coordinate/frame changes. Therefore searching for LV is one of the most sensitive ways of looking for new physics, either new interactions or modifications of known ones. Energy dissipation/Cerenkov radiation is shown to be a generic feature of LV in QFT. A general computation is done in strongly coupled theories with gravity duals. It is shown that in scale invariant regimes, the energy dissipation rate depends non-triviallly on two characteristic exponents, the Lifshitz exponent and the hyperscaling violation exponent.

hep-th↗

arXiv2012

The holographic quantum effective potential at finite temperature and density

We develop a formalism that allows the computation of the quantum effective potential of a scalar order parameter in a class of holographic theories at finite temperature and charge density. The effective potential is a valuable tool for studying the ground state of the theory, symmetry breaking patterns and phase transitions. We derive general formulae for the effective potential and apply them to determine the phase transition temperature and density in the scaling region.

hep-th↗

arXiv2012

Heavy quarks in a magnetic field

The motion of a heavy charged quark in a magnetic field is analyzed in the vacuum of strongly coupled CFT. The motion of the quark is dissipative. It moves in spiral until it eventually comes to rest. The world-sheet geometry is locally AdS_2 but has a time dependent horizon. The string profile in the static gauge extends from the boundary till a point where an embedding singularity exists. Connections with other circular string motions are established.

hep-th↗

arXiv2012

Holographic quantum criticality and strange metal transport

A holographic model of a quantum critical theory at a finite but low temperature, and finite density is studied. The model exhibits non-relativistic z=2 Schrödinger symmetry and is realized by the Anti-de-Sitter-Schwarzschild black hole in light-cone coordinates. Our approach addresses the electrical conductivities in the presence or absence of an applied magnetic field and contains a control parameter that can be associated to quantum tuning via charge carrier doping or an external field in correlated electron systems. The Ohmic resistivity, the inverse Hall angle, the Hall coefficient and the magnetoresistance are shown to be in good agreement with experimental results of strange metals at very low temperature. The holographic model also predicts new scaling relations in the presence of a magnetic field.

cond-mat.str-el↗