arXiv subjects

Horatiu Nastase

Publications and source records attributed to Horatiu Nastase.

At least 55 records · Page 3Linked to original sources

arXiv2021

A 4D duality web

We construct a web of non-supersymmetric dualities in four spacetime dimensions for theories with theta and Maxwell terms. Our construction mirrors the recipe used in (2+1)-dimensions to demonstrate a similar duality for theories with Chern-Simons terms. As in the 3-dimensional case, the web consists of boson-boson, fermion-fermion and boson-fermion dualities, any one of which can be taken as a seed for the remaining two. To be concrete, we begin by constructing the basic bosonization duality which we then use to generate the web, using an analog of the 3-dimensional massive construction given in \cite{Nastase:2017gxr} . The resulting 4-dimensional duality web is best understood as an extension of the, by now well-known, 3-dimensional case due to its somewhat singular nature. We conjecture that this is the final thread in a multi-dimensional duality web that connects low energy theories in 4-, 3- and 2-spacetime dimensions and speculate on its application to 3-dimensional topological insulators.

hep-th↗

arXiv2021

Wiedemann-Franz laws and $Sl(2,\mathbb{Z})$ duality in AdS/CMT holographic duals and one-dimensional effective actions for them

In this paper we study the Wiedemann-Franz laws for transport in 2+1 dimensions, and the action of $Sl(2,\mathbb{Z})$ on this transport, for theories with an AdS/CMT dual. We find that $Sl(2,\mathbb{Z})$ restricts the RG-like flow of conductivities and that the Wiedemann-Franz law is $\bar L =\barκ/(Tσ)=cg_4^2π/3$, from the weakly coupled} gravity dual. In a self-dual theory this value is also the value of $L =κ/(Tσ)$ in the weakly coupled field theory description. Using the formalism of a 0+1 dimensional effective action for both generalized $SYK_q$ models and the $AdS_4$ gravity dual, we calculate the transport coefficients and show how they can be matched at large $q$. We construct a generalization of this effective action that is invariant under $Sl(2,\mathbb{Z})$ and can describe vortex conduction and integer quantum Hall effect.

hep-th↗

arXiv2021

Soliton, breather and shockwave solutions of the Heisenberg and the $T\bar T$ deformations of scalar field theories in 1+1 dimensions

In this note we study soliton, breather and shockwave solutions in certain two dimensional field theories. These include: (i) Heisenberg's model suggested originally to describe the scattering of high energy nucleons (ii) $T\bar T$ deformations of certain canonical scalar field theories with a potential. We find explicit soliton solutions of these models with sine-Gordon and Higgs-type potentials. We prove that the $T\bar T$ deformation of a theory of a given potential does not correct the mass of the soliton of the undeformed one. We further conjecture the form of breather solutions of these models. We show that certain $T\bar T$ deformed actions admit shockwave solutions that generalize those of Heisenberg's Lagrangian.

hep-th↗

arXiv2021

A $T\bar T$-like deformation of the Skyrme model and the Heisenberg model of nucleon-nucleon scattering

The Skyrme model, though it admits correctly a wide range of static properties of the nucleon, does not seem to reproduce properly the scattering behavior of nucleons at high energies. In this paper we present a $T\bar T$-like deformation of it, inspired by a 1+1 dimensional model, in which boosted nucleons behave like shock waves. The scattering of the latter saturates the Froissart bound. We start by showing that 1+1 dimensional $T\bar T$ deformations of the free abelian pion action are in fact generalizations of the old Heisenberg model for nucleon-nucleon scattering, yielding the same saturation of the Froissart bound. We then deform the strong coupling limit of the bosonized action of multi-flavor QCD in two dimensions using the $T\bar T$ deformation of the WZW action with a mass term. We derive the classical soliton solution that corresponds to the nucleon, determine its mass and discuss its transformation into a shock-wave upon boosting. We uplift this action into a 3+1 dimensional $T\bar T$-like deformation of the Skyrme action. We compare this deformed action to that of chiral perturbation theory. A possible holographic gravity dual interpretation is explored.

hep-th↗

arXiv2020

The monopole problem in holographic cosmology

In this letter we clarify that the monopole problem can always be solved in bosonic holographic cosmology, by the analogue of "dilution" in inflation, which is the fact that the {\em electric} current is an irrelevant operator in the dual field theory. We show that not only specific toy models solve the problem, but any purely bosonic member of the phenomenological class, of super-renormalizable, generalized conformal symmetric models.

hep-th↗

arXiv2020

Holographic cosmology solutions of problems with pre-inflationary cosmology

In this paper we describe in detail how to solve the problems of pre-inflationary cosmology within the holographic cosmology model of McFadden and Skenderis \cite{McFadden:2009fg}. The solutions of the smoothness and horizon problems, the flatness problem, the entropy and perturbation problems and the baryon asymmetry problem are shown, and the mechanisms for them complement the inflationary solutions. Most of the paper is devoted to the solution of the monopole relic problem, through a detailed calculation of 2-loop correlators of currents in a toy model which we perform in $d$ dimensions, in order to extract its leading dependece on $g^2_{\rm eff}=g^2_{YM}N/q$ and find a dilution effect. Taken together with the fact that holographic cosmology gives as good a fit to CMBR as the standard paradigm of $Λ$ CDM with inflation, it means holographic cosmology extends the inflationary paradigm into new corners, explorable only through a dual perturbative field theory in 3 dimensions.

hep-th↗

arXiv2019

Holography for the very early Universe and the classic puzzles of Hot Big Bang cosmology

We show that standard puzzles of hot Big Bang cosmology that motivated the introduction of cosmological inflation, such as the smoothness and horizon problem, the flatness problem and the relic problem are also solved by holographic models for very early universe based on perturbative three dimensional QFT. In the holographic setup, cosmic evolution is mapped to inverse renormalization group (RG) flow of the dual QFT, and the resolution of the puzzles relies on properties of the RG flow.

hep-th↗

arXiv2019

Holographic cosmology from "dimensional reduction" of ${\cal N}=4$ SYM vs. $AdS_5\times S^5$

We propose a way to obtain holographic cosmology models for 3+1 dimensional cosmologies vs. 3 dimensional field theories from a "dimensional reduction" procedure, obtained by integrating over the time direction, of (modifed) standard holographic duals of 3+1 dimensional field theories. The example of a modified ${\cal N}=4$ SYM vs. $AdS_5\times S^5$ is presented, and in perturbation theory doesn't match observations, though at strong coupling it might. But the proposed mechanism is more general, and it could in principle be applied to other top down holographic models.

hep-th↗

arXiv2019

Solution of the cosmological constant problem within holographic cosmology

Within the holographic cosmology paradigm, specifically the model of McFadden and Skenderis, but more generally than that, the cosmological constant is found to naturally flow from a large value, to a small value, which can even be as low as the needed $\sim 10^{-120}$ times the original, along with the dual RG flow. Within this context then, the cosmological constant problem is mapped to a simple quantum field theory property, even though the exact mechanism for it in gravity is still obscure. I consider several examples of gravity duals to explain the mechanism.

hep-th↗

arXiv2019

Causal faster than light travel from travel-localized second time coordinate

I present a {\em general relativistic} model with a compactified second time coordinate that {\em a priori} allows for causal, yet faster than light travel in the background of a FLRW geometry, by local modification of a higher dimensional background geometry, specifically with respect to the radius of the compactified time coordinate. The modification can be induced via the fields of the model. I show that one cannot convert (as possible in special relativistic models, or simple general relativistic models) the super-luminality into closed time-like loops violating causality, due to a novel combination of factors, at least for $v_{\rm max}\leq \sqrt{2}$. The physics of the second time is constrained by postulates derived from reasonable physical assumptions. I comment on the possibility of experimental implications of the model.

hep-th↗

arXiv2019

One-dimensional bosonization and the SYK model

We explore the possibility of extending the familiar bosonization of two dimensions to $(0+1)$- dimensional systems with a large number of degrees of freedom. As an application of this technique, we consider a class of SYK-type models, and argue that the corresponding action on the gravity dual of the SYK model is given by an STS sequence of dualities.

hep-th↗

arXiv2019

S-duality, entropy function and transport in $AdS_4/CMT_3$

In this paper we consider Abelian vector plus scalar holographic gravity models for 2+1 dimensional condensed matter transport, and the effect of S-duality on them. We find the transport coefficients from the electric and heat currents via usual membrane paradigm-type calculations, and the effect of S-duality on them. We study the same system also by using the entropy function formalism in the extremal case, and the formalism of holographic Stokes equations, in the case of one-dimensional lattices. We study a few generalizations that appear when considering a supergravity-inspired model, and apply the entropy function method for them.

hep-th↗

arXiv2019

Particle-vortex duality and theta terms in AdS/CMT applications

In this paper we study particle-vortex duality and the effect of theta terms from the point of view of AdS/CMT constructions. We can construct the duality in 2+1 dimensional field theories with or without a Chern-Simons term, and derive an effect on conductivities, when the action is viewed as a response action. We can find its effect on 3+1 dimensional theories, with or without a theta term, coupled to gravity in asymptotically AdS space, and derive the resulting effect on conductivities defined in the spirit of AdS/CFT. AdS/CFT then relates the 2+1 dimensional and the 3+1 dimensional cases naturally. Quantum gravity corrections, as well as more general effective actions for the abelian vector, can be treated similarly. We can use the fluid/gravity correspondence, and the membrane paradigm, to define shear and bulk viscosities $η$ and $ζ$ for a gravity plus abelian vector plus scalar system near a black hole, and define the effect of the S-duality on it.

hep-th↗

arXiv2019

Towards deriving the AdS/CFT correspondence

I present the sketch of a "physicist's" derivation of the AdS/CFT correspondence for the original pair, string theory in $AdS_5\times S^5$ vs. ${\cal N}=4$ SYM, based on the pp wave limit, and deviations from it. I show that one can reverse the logic, and derive the action of ${\cal N}=4$ SYM, as kinetic terms plus vertices, as well as the elements of its path integral, from string theory on the pp wave. One can also treat consistently deviations from the "strings on the pp wave" limit, starting from the SYM side, and a priori reconstruct the full $AdS_5\times S^5$ geometry perturbatively, as well as full perturbative string theory on it.

hep-th↗

arXiv2018

Hopfion solutions in gravity and a null fluid/gravity conjecture

We conjecture an extension of the fluid/gravity correspondence to the null pressureless fluid case via gravitational shockwave solutions, and use it to propose an embedding of the fluid Hopfion in gravity. A nonlinear gravitational "helicity" is also proposed, analogous with the helicity of electromagnetism and fluid dynamics.

hep-th↗

arXiv2018

Conformal inflation with chameleon coupling

We investigate the possibility that the inflaton, in particular in conformal inflation models, is also a chameleon, i.e. that it couples to the energy density of some heavy non-relativistic matter present during inflation. We find new and interesting attractor behaviours, either prolonging inflation, or changing the observables $n_s,r$, depending on the sign of the chameleon coupling exponent. We also check that the chameleon coupling with the heavy matter field strongly suppress entropy modes during inflation.

hep-th↗

arXiv2018

Lagrangian formulation, generalizations and quantization of null Maxwell's knots

Knotted solutions to electromagnetism are investigated as an independent subsector of the theory. We write down a Lagrangian and a Hamiltonian formulation of Bateman's construction for the knotted electromagnetic solutions. We introduce a general definition of the null condition and generalize the construction of Maxwell's theory to massless free complex scalar, its dual two form field, and to a massless DBI scalar. We set up the framework for quantizing the theory both in a path integral approach, as well as the canonical Dirac method for a constrained system. We make several observations about the semi-classical quantization of systems of null configurations.

hep-th↗

arXiv2017

Penrose limits of Abelian and non-Abelian T-duals of $AdS_5\times S^5$ and their field theory duals

We consider the backgrounds obtained by Abelian and non-Abelian T-duality applied on $AdS_5\times S^5$. We study geodesics, calculate Penrose limits and find the associated plane-wave geometries. We quantise the weakly coupled type-IIA string theory on these backgrounds. We study the BMN sector, finding operators that wrap the original quiver CFT. For the non-Abelian plane wave, we find a 'flow' in the frequencies. We report some progress to understand this, in terms of deconstruction of a higher dimensional field theory. We explore a relation with the plane-wave limit of the Janus solution, which we also provide.

hep-th↗