arXiv subjects

Elias Kiritsis

Publications and source records attributed to Elias Kiritsis.

At least 19 recordsLinked to original sources

arXiv2026

The Tachyon Chern-Simons action with a generic tachyon field, and baryons in V-QCD

Consistency with global flavor anomalies requires the presence of Chern-Simons terms in holographic models of QCD. Such terms are analyzed in a setup arising in the holographic V-QCD model, where chiral symmetry breaking is implemented through the condensation of a complex scalar field, the tachyon. Using the superconnection formalism, the Tachyon-Chern-Simons terms are constructed explicitly in the general case, where the tachyon is any complex matrix in flavor space. This general case covers, among other things, backgrounds where different quark flavors have different masses. These new results are used to analyze the structure of the baryon solutions in the presence of nonzero quark masses. Expressions for the baryon number current and the total baryon number are found, and the baryon number is shown to be equal to the topological instanton number of the baryon solution. The effective four-dimensional pion action is analyzed and is shown to reproduce the chiral Lagrangian, including the Skyrme and Wess-Zumino-Witten terms.

hep-th↗

arXiv2026

Flavour current correlators and the non-Abelian hydrodynamic approximation: the charged sector

Flavor-current correlators are studied in strongly-coupled dense (holographic) matter, at finite quark chemical potential $μ_q$ and finite isospin asymmetry. The non-Abelian hydrodynamic description of the charged currents is derived in the presence of an isospin chemical potential $μ_3$. The two-point correlators of charged currents are then computed holographically at finite quark and isospin chemical potentials. In the near-extremal hydrodynamic regime, $ω, k, T, μ_3 \ll μ\equiv \sqrt{μ_q^2+μ_3^2}$, relevant for cold strongly coupled matter, the IR properties of the correlators are studied. It is shown that in this regime, the correlators agree with the non-Abelian hydrodynamic predictions. Therefore, the traditional regime of validity of standard hydrodynamics extends beyond $ω, k \ll T \ll μ$ to the so-called extended hydrodynamic regime $T\ll ω, k \ll μ$. The holographic product formula is applied to the present non-Abelian system, and is used to propose an extended hydrodynamic approximation capturing both hydrodynamic-like poles and the leading effect of AdS$_2$ poles, by resumming the low-$ω$ logarithms. The results are verified through a detailed numerical analysis of the exact correlators and quasi-normal mode spectrum.

hep-th↗

arXiv2026

The phase diagram of confining holographic theories on constant curvature manifolds in the presence of a $θ$-angle

Large families of confining holographic QFTs, described by Einstein-Dilaton gravity, are considered on constant-curvature manifolds in the presence of a $θ$-angle. The space of ground states of such theories is explored as a function of the UV parameters, namely the dimensionless curvature and the $θ$ angle. The free energy is computed, and the phase structure is determined. For constant negative curvature manifolds, we find solutions dual to single QFTs as well as solutions describing interfaces. The single QFTs exhibit an infinite family of saddle points, with the leading one dominating the gravitational path integral and no phase transitions present. For constant positive curvature manifolds, like de Sitter, the ($θ$-angle, curvature) phase diagram exhibits both first and second order phase transitions, as a function of the class of theories considered. We also show that when $θ=0$, a holographic Vafa-Witten-like theorem can be proven.

hep-th↗

arXiv2026

Holographic shear correlators at low temperatures, and quantum $η/s$

The strongly-coupled 3-dimensional theory, holographically dual to black branes at fixed chemical potential $\muext$ and temperature $T \ll μ$ is considered in AdS$_4$ Einstein-Maxwell theory. The retarded Green's functions at frequency $ω$ is calculated using holography in the regime $ω, T \ll \muext$ but otherwise arbitrary. When the transverse space has finite volume, there is a non-zero energy scale $E_\text{gap}$, scaling as $1/μ$ for large $μ$, below which quantum-gravitational corrections due to the fluctuations of the nearly-gapless Schwarzian modes become important. Such corrections to the retarded Green's function are calculated at different relative values of $ω$, $T$, and $E_\text{gap}$. The $ω\to 0$ limit is used to define the shear viscosity $η$. As the temperature is lowered below $μ$, quantum corrections are found to increase the value of $η$ with respect to its semiclassical value.The quantum-corrected result for $η$ diverges as $\sqrt{E_\text{gap}/T}$ at $T \ll E_\text{gap}$, in accord with corresponding results for the absorption cross section. The quantum result for the ratio $η/s$, where $s$ is the entropy density, dips below the semiclassical limit of $1/4π$ when $E_\text{gap} \ll T \ll μ$,then turns back to increase towards lower temperatures, and finally diverges at temperatures much below $E_\text{gap}$.

hep-th↗

arXiv2025

de Sitter versus Anti de Sitter flows and the (super)gravity landscape: Part II

Generic solutions are studied in Einstein-scalar gravity in an ansatz that can interpolate between de Sitter and Anti-de Sitter regimes. The scalar potential is arbitrary. All solutions are determined by their end-points in the scalar field space. All such end-points are classified. This provides a complete classification and characterization of the full space of regular solutions. It is shown that there are no regular (Centaur) solutions that interpolate between an AdS boundary and a dS interior, within our ansatz, when $d>2$. This no-go theorem persists in the presence of multiple scalar fields with a non-trivial field space metric. The Gubser classification of regular solutions is also upgraded to include cases that are not Lorentz invariant and do not contain AdS boundaries.

hep-th↗

arXiv2025

On the spectra of holographic QFTs on constant curvature manifolds

We analyze linear fluctuations of five-dimensional Einstein-Dilaton theories dual to holographic quantum field theories defined on four-dimensional de Sitter and Anti-de Sitter space-times. We identify the physical propagating scalar and tensor degrees of freedom. For these, we write the linearized bulk field equations as eigenvalue equations. In the dual QFT, the eigenstates correspond to towers of spin-0 and spin-2 particles propagating on $(A)dS_4$ associated to gauge-invariant composite states. Using particular care in treating special ``zero-modes,'' we show in general that, for negative curvature, the particle spectra are always discrete, whereas for positive curvature they always have a continuous component starting at $m^2 = (9/4)α^{-2}$, where $α$ is the $(A)dS_4$ radius. We numerically compute the spectra in a concrete model characterized by a polynomial dilaton bulk potential admitting holographic RG-flow solutions with a UV and IR fixed points. In this case, we find no discrete spectrum and no perturbative instabilities.

hep-th↗

arXiv2025

Improved Holographic QCD on a Curved Background: an Application of Dynamical System Theory in Holography

The finite-curvature phase diagram of IHQCD, a bottom-up holographic model for large $N_c$ non-supersymmetric YM$_4$, is investigated. This holographic theory belongs to a class of Einstein-Dilaton theories that exhibit no scaling in the IR. We use advanced techniques from dynamical system theory to address this problem that is harder than other holographic setups. We classify all solutions where the dual theory is defined on a constant curvature manifold, both with positive and negative curvature. For general theories in this class a quantum phase transition occurs at finite curvature. For IHQCD in particular, we find that the phase transition occurs at zero curvature.

hep-th↗

arXiv2025

Holographic confining theories on space-times with constant positive curvature

Varying the curvature, quantum phase transitions are investigated in holographic confining QFTs defined on a fixed constant positive curvature background. We find a competition between two branches of solutions and a phase transition as one varies the space-time curvature. The low-curvature phase has the same kind of IR geometry as the flat-space solution, while the high-curvature phase has a regular interior. We argue that, depending on the leading asymptotic exponent of the scalar potential, the transition may be first-order or higher-order.

hep-th↗

arXiv2024

Scattering, Absorption and Emission of Highly Excited Strings

We study tree-level scattering processes of arbitrary string states using the DDF formalism and suitable coherent vertex operators. We obtain new exact compact formulae for heavy-heavy-light-light scattering amplitudes in open or closed bosonic string theories, and derive explicit exact expressions for the absorption cross-sections, and corresponding emission rates, of highly excited string states using the optical theorem and time reversal symmetry. We show that these expressions are independent of the microscopic structure of the excited string states without averaging. For the absorption of massless modes in open string theory, in particular, we find a constant, frequency-independent cross-section. In contrast, the corresponding cross-section for the absorption of massless modes by excited closed strings depends linearly on the frequency, implying a non-trivial grey-body factor. In both cases, at energies below the scale set by the mass of the highly excited strings, we find emission rates with a Boltzmann factor at Hagedorn temperature.

hep-th↗

arXiv2024

Phases and Phase transitions of U(1)$\times$SU(2) symmetric holographic matter

The phase diagram and symmetry breaking patterns of a holographic CFT with U(1)$\times$SU(2) symmetry are analyzed using the simplest holographic action, namely Einstein-Yang-Mills (YM) theory with a negative cosmological constant. This is relevant for both condensed matter and QCD applications. With a U(1) and an "isospin" chemical potential turned on, we determine all possible symmetry breaking patterns, which are associated to the condensation of spin-one order parameters. The possible IR asymptotics of the Einstein-YM solutions are derived analytically, both for 2+1 and 3+1 boundary dimensions. The competing solutions are then computed numerically, both at zero and non-zero temperature, from which the full three-dimensional phase diagram is determined. We find a surface of second order phase transitions that separate uncondensed and condensed phases. In some regions with a large fraction of charged to neutral degrees of freedom, the phase transition becomes first order.

hep-th↗

arXiv2024

On holographic confining QFTs on AdS

Holographic quantum field theories that confine in flat space, are considered on a fixed AdS space. The space of holographic solutions for such theories is constructed and three types of regular solutions are found. Theories with two AdS boundaries provide interfaces between two confining theories. Theories with a single AdS boundary correspond to ground states of a single confining theory on AdS. We find solutions without a boundary, whose interpretation is not obvious. There is also a special limiting solution that oscillates an infinite number of times around the UV fixed point. We analyze in detail the holographic dictionary for the one-boundary solutions and compute the free energy. No (quantum) phase transitions are found when we change the curvature. We find an infinite number of pure vev solutions, but no CFT solution without a vev. We also compute the free energy of the interface solutions. We find that the product saddle points have always lower free energy than the connected solutions. This implies that in such interfaces, normalized cross-correlators vanish exponentially in $N_c^2$.

hep-th↗

arXiv2024

Matching the Vilkovisky-DeWitt Effective Action of Quantum Gravity to String Theory

In this work, we discuss the matching of the Vilkovisky-DeWitt effective action of quantum gravity to an example of an ultra-violet complete theory of quantum gravity. We show how this matching enables a calculation of the local Wilson coefficients of the effective action. We provide several examples in string theory. Moreover, we discuss the matching conditions within the context of the swampland program.

hep-th↗

arXiv2024

A dynamical inflaton coupled to strongly interacting matter

According to the inflationary theory of cosmology, most elementary particles in the current universe were created during a period of reheating after inflation. In this work we self-consistently couple the Einstein-inflaton equations to a strongly coupled quantum field theory (QFT) as described by holography. We show that this leads to an inflating universe, a reheating phase and finally a universe dominated by the QFT in thermal equilibrium.

hep-th↗

arXiv2023

Quantum (in)stability of maximally symmetric space-times

Classical gravity coupled to a CFT$_4$ (matter) is considered. The effect of the quantum dynamics of matter on gravity is studied around maximally symmetric spaces (flat, de Sitter and Anti de Sitter). The structure of the graviton propagator is modified and non-trivial poles appear due to matter quantum effects. The position and residues of such poles are mapped as a function of the relevant parameters, the central charge of the CFT$_4$, the two $R^2$ couplings of gravity as well as the curvature of the background space-time. The instabilities induced are determined. Such instabilities can be important in cosmology as they trigger the departure from de Sitter space and in some regions of parameters are more important than the well-known scalar instabilities. It is also determined when the presence of such instabilities is unreliable if the associated scales are larger than the ``species" cutoff of the gravitational theory.

gr-qc↗

arXiv2023

Holographic CFTs on $AdS_d\times S^n$ and conformal defects

We consider ($d+n+1$)-dimensional solutions of Einstein gravity with constant negative curvature. Regular solutions of this type are expected to be dual to the ground states of ($d+n$)-dimensional holographic CFTs on $AdS_d\times S^n$. Their only dimensionless parameter is the ratio of radii of curvatures of $AdS_d$ and $S^n$. The same solutions may also be dual to $(d-1)$-dimensional conformal defects in holographic QFT$_{d+n}$. We solve the gravity equations with an associated conifold ansatz, and we classify all solutions both singular and regular by a combination of analytical and numerical techniques. There are no solutions, regular or singular, with two boundaries along the holographic direction. Out of the infinite class of regular solutions, only one is diffeomorphic to $AdS_{d+n+1}$ and another to $AdS_d\times AdS_{n+1}$. For the regular solutions, we compute the on-shell action as a function of the relevant parameters.

hep-th↗

arXiv2023

Quasi-extremal primordial black holes are a viable dark matter candidate

Black hole evaporation is generally considered inevitable for low-mass black holes, yet there is no confirmation of this remarkable hypothesis. Here, we propose a phenomenological model that appeals to the possible survival of light quasi-extremal primordial black holes as a significant dark matter component and show that the related cosmological and astrophysical constraints disappear for reasonable degrees of quasi-extremality. The results obtained are general, conservative and should be taken as a proof of principle for future, model-specific analyses.

astro-ph.CO↗

arXiv2023

Holographic RG flows on Squashed $S^3$

Holographic RG flows dual to QFTs on a squashed $S^3$ are considered in the framework of Einstein dilaton gravity in four dimensions. A general dilaton potential is used and flows are driven by a scalar relevant operator. The general properties of such flows are analysed and the UV and IR asymptotics are computed. Exotic asymptotics are found, that are different from the standard Fefferman-Graham asymptotics.

hep-th↗

arXiv2023

de Sitter versus Anti de Sitter flows and the (super)gravity landscape

Generic solutions are studied in Einstein-scalar gravity in an ansatz that can interpolate between de Sitter and Anti-de Sitter regimes. The classification of regular solutions of \cite{exotic} is first extended to the dS regime. This implies, among others, the existence of cosmic clocks that reverse direction without passing through a curvature singularity. We then consider an ansatz for solutions that interpolate between the dS and AdS regimes. The structure of such more general solutions and their singularities are studied. It is shown that there are no regular solutions that interpolate between dS and AdS extrema for generic potentials. This is unlike the Centaur solutions that were shown to exist in two bulk dimensions. We also comment on the potential interplay with recent dS conjectures and the dS BF bounds.

hep-th↗