arXiv subjects

J. G. Russo

Publications and source records attributed to J. G. Russo.

At least 19 recordsLinked to original sources

arXiv2023

RG Flows and Stability in Defect Field Theories

We investigate defects in scalar field theories in four and six dimensions in a double-scaling (semiclassical) limit, where bulk loops are suppressed and quantum effects come from the defect coupling. We compute $β$-functions up to four loops and find that fixed points satisfy dimensional disentanglement -- i.e. their dependence on the space dimension is factorized from the coupling dependence -- and discuss some physical implications. We also give an alternative derivation of the $β$ functions by computing systematic logarithmic corrections to the Coulomb potential. In this natural scheme, $β$ functions turn out to be a gradient of a `Hamiltonian' function ${\cal H}$. We also obtain closed formulas for the dimension of scalar operators and show that instabilities do not occur for potentials bounded from below. The same formulas are reproduced using Rigid Holography.

hep-th↗

arXiv2023

Defects, Rigid Holography and $C$-theorems

We consider a general scalar QFT with a linear defect in $D=4-ε$ and a surface defect in $D=6-ε$. Using holography and the Hamilton-Jacobi formalism, we show that the $β$ functions controlling the defect RG flow are the gradient of the entropy function. In the case of conformal field theories, this allows the proof that the relevant $C$-functions decrease monotonically along the RG flow. We provide evidence that this property also holds in the full quantum theory for general scalar field theories. An obstruction to the gradient property seems to appear at two loop order when fermions are added.

hep-th↗

arXiv2022

Defects in scalar field theories, RG flows and Dimensional Disentangling

We consider defect operators in scalar field theories in dimensions $d=4-ε$ and $d=6-ε$ with self-interactions given by a general marginal potential. In a double scaling limit, where the bulk couplings go to zero and the defect couplings go to infinity, the bulk theory becomes classical and the quantum defect theory can be solved order by order in perturbation theory. We compute the defect $β$ functions to two loops and study the Renormalization Group flows. The defect fixed points can move and merge, leading to fixed point annihilation; and they exhibit a remarkable factorization property where the $ε$-dependence gets disentangled from the coupling dependence.

hep-th↗

arXiv2022

Wilson loops in Large Symmetric Representations through a Double-Scaling Limit

We derive exact formulas for circular Wilson loops in the $\mathcal{N}=4$ and $\mathcal{N}=2^{* }$ theories with gauge groups $U(N)$ and $SU(N)$ in the $k$-fold symmetrized product representation. The formulas apply in the limit of large $k$ and small Yang-Mills coupling $g$, with fixed effective coupling $κ\equiv g^2k$, and for any finite $N$. In the $SU(2)$ and $U(2)$ cases, closed analytic formulas are obtained for any $k$, while the $1/k$ series expansions are asymptotic. In the $N\gg 1$ limit, with $N\ll k$, there is an overlapping regime where the formulas can be confronted with results from holography. Simple formulas for correlation functions between the $k$-symmetric Wilson loops and chiral primary operators are also given.

hep-th↗

arXiv2022

A dilaton-axion model for string cosmology

The generic scale-invariant theory of an axion and a dilaton coupled to gravity in $d$-dimensions is generalized to a `universal' one-axion model with two dilatons that reproduces itself under consistent dimensional-reduction/truncation. Flat FLRW cosmologies are shown to correspond to trajectories of a three-dimensional autonomous dynamical system, which we analyse with a focus on accelerated cosmic expansion, deriving the precise swampland bounds that exclude eternal acceleration. We also show that for two sets of values of its three independent parameters, the model is a consistent truncation of maximal `massive' supergravity theories arising from string/M-theory; for these maximal-supergravity parameter values the FLRW cosmologies include some with a transient de Sitter-like phase, but not the recurring de Sitter-like phase or eternal cosmic acceleration that is possible for other parameter values.

hep-th↗

arXiv2021

Time-dependent compactification to de Sitter space: a no-go theorem

It is known that the Einstein gravitational field equations in $D>4$ spacetime dimensions have no time-independent non-singular compactification solutions to de Sitter space if the $D$-dimensional stress tensor satisfies the Strong Energy Condition (SEC). Here we show, by example, that the SEC alone does not exclude time-dependent non-singular compactifications to de Sitter space, in Einstein conformal frame. However, this possibility is excluded by the combined SEC and Null Energy Condition (NEC) because the NEC forces a time-evolution towards a singular $D$-metric.

hep-th↗

arXiv2021

Correlation functions in finite temperature CFT and black hole singularities

We compute thermal 2-point correlation functions in the black brane $AdS_5$ background dual to 4d CFT's at finite temperature for operators of large scaling dimension. We find a formula that matches the expected structure of the OPE. It exhibits an exponentiation property, whose origin we explain. We also compute the first correction to the two-point function due to graviton emission, which encodes the proper time from the event horizon to the black hole singularity.

hep-th↗

arXiv2021

Thermal correlation functions in CFT and factorization

We study 2-point and 3-point functions in CFT at finite temperature for large dimension operators using holography. The 2-point function leads to a universal formula for the holographic free energy in $d$ dimensions in terms of the $c$-anomaly coefficient. By including $α'$ corrections to the black brane background, one can reproduce the leading correction at strong coupling. In turn, 3-point functions have a very intricate structure, exhibiting a number of interesting properties. In simple cases, we find an analytic formula, which reduces to the expected expressions in different limits. When the dimensions satisfy $Δ_i= Δ_j+ Δ_k$, the thermal 3-point function satisfies a factorization property. We argue that in $d>2$ factorization is a reflection of the semiclassical regime.

hep-th↗

arXiv2019

Properties of the partition function of ${\cal N}=2$ supersymmetric QCD with massive matter

We study the different quantum phases that occur in massive ${\cal N}=2$ supersymmetric QCD with gauge groups $SU(2)$ and $SU(3)$ as the coupling $Λ/M$ is gradually increased from 0 to infinity. The phases can be identified by computing the exact partition function by saddle-points, combining supersymmetric localization and the Seiberg-Witten formalism. In all cases, we find two phases, a weak coupling and a strong coupling phase, separated by a critical point described by a superconformal field theory or involving superconformal sectors. In crossing the critical point, the dominant saddle-point hops from one singularity of the curve to another one. The theories seem to undergo a second-order phase transition with divergent susceptibility.

hep-th↗

arXiv2019

The large charge limit of scalar field theories and the Wilson-Fisher fixed point at $ε=0$

We study the sector of large charge operators $ϕ^n$ ($ϕ$ being the complexified scalar field) in the $O(2)$ Wilson-Fisher fixed point in $4-ε$ dimensions that emerges when the coupling takes the critical value $g\sim ε$. We show that, in the limit $g\to 0$, when the theory naively approaches the gaussian fixed point, the sector of operators with $n\to \infty $ at fixed $g\,n^2\equiv λ$ remains non-trivial. Surprisingly, one can compute the exact 2-point function and thereby the non-trivial anomalous dimension of the operator $ϕ^n$ by a full resummation of Feynman diagrams. The same result can be reproduced from a saddle point approximation to the path integral, which partly explains the existence of the limit. Finally, we extend these results to the three-dimensional $O(2)$-symmetric theory with $(\barϕ\,ϕ)^3$ potential.

hep-th↗

arXiv2019

Late-time Cosmic Acceleration from Compactification

We investigate the implications of energy conditions on cosmological compactification solutions of the higher-dimensional Einstein field equations. It is known that the Strong Energy Condition forbids time-independent compactifications to de Sitter space but allows time-dependent compactifications to other (homogeneous and isotropic) expanding universes that undergo a {\it transient} period of acceleration. Here we show that the same assumptions allow compactification to FLRW universes undergoing {late-time} accelerated expansion; the late-time stress tensor is a perfect fluid but with a lower bound on the pressure/energy-density ratio that excludes de Sitter but allows accelerated power-law expansion. The compact space undergoes a decelerating expansion that leads to decompactification, but on an arbitrarily long timescale.

hep-th↗

arXiv2017

N=2 Chern-Simons-Matter Theories Without Vortices

We study ${\cal N}=2$ Chern-Simons-matter theories with gauge group $U_{k_1}(1)\times U_{k_2}(1)$. We find that, when $k_1+k_2=0$, the partition function computed by localization dramatically simplifies and collapses to a single term. We show that the same condition prevents the theory from having supersymmetric vortex configurations. The theories include mass-deformed ABJM theory with $U(1)_{k}\times U_{-k}(1)$ gauge group as a particular case. Similar features are shared by a class of CS-matter theories with gauge group $U_{k_1}(1)\times \cdots \times U_{k_N}(1)$.

hep-th↗

arXiv2013

Localization at Large N

We review how localization is used to probe holographic duality and, more generally, non-perturbative dynamics of four-dimensional N=2 supersymmetric gauge theories in the planar large-N limit.

hep-th↗

arXiv2013

Massive N=2 Gauge Theories at Large N

Using exact results obtained from localization on S^4, we explore the large N limit of N=2 super-Yang-Mills theories with massive matter multiplets. We focus on three cases: N=2* theory, describing a massive hypermultiplet in the adjoint representation, SU(N) super-Yang-Mills with 2N massive hypermultiplets in the fundamental, and super-QCD with massive quarks. When the radius of the four-sphere is sent to infinity the theories at hand are described by solvable matrix models, which exhibit a number of interesting phenomena including quantum phase transitions at finite 't Hooft coupling.

hep-th↗

arXiv2013

Large N Limit of N=2 SU(N) Gauge Theories from Localization

We study N=2 Yang-Mills theory on S^4 in the large-N limit. We find that on a large sphere Wilson loops obey a perimeter law and that the free energy grows quadratically with the radius of the sphere. We also comment on the large-N limit of the N=2* theory, and on the free energy in N=2 and N=4 superconformal theories.

hep-th↗

arXiv2013

Global Supersymmetry on Curved Spaces in Various Dimensions

We propose methods towards a systematic determination of d dimensional curved spaces where Euclidean field theories with rigid supersymmetry can be defined. The analysis is carried out from a group theory as well as from a supergravity point of view. In particular, by using appropriate gauged supergravities in various dimensions we show that supersymmetry can be defined in conformally flat spaces, such as non-compact hyperboloids $H^{n+1}$ and compact spheres $S^n$ or --by turning on appropriate Wilson lines corresponding to R-symmetry vector fields-- on $S^1 x S^n$, with n<6. By group theory arguments we show that Euclidean field theories with rigid supersymmetry cannot be consistently defined on round spheres $S^d$ if d>5 (despite the existence of Killing spinors). We also show that distorted spheres and certain orbifolds are also allowed by the group theory classification.

hep-th↗

arXiv2010

Large spin expansion of semiclassical 3-point correlators in AdS_5 x S^5

3-point correlators in AdS_5xS^5 string theory in which two states are "heavy" (have large quantum numbers) and the third is "light" (here chosen as chiral primary scalar) can be computed semiclassically in terms of the "light" vertex operator evaluated on the classical string solution sourced by the two "heavy" operators. We observe that in the case when the "heavy" operators represent BPS states there is an ambiguity in the computation depending on whether the mass shell (or marginality) condition is imposed before or after integration over the world sheet. We show that this ambiguity is resolved in a universal way by defining the BPS correlator as a limit of the one with non-BPS "heavy" states. We consider several examples with "heavy" states represented by folded or circular spinning strings in AdS_5xS^5 that admit a point-like BMN-type limit when one S^5 spin J is much larger than the others. Remarkably, in all of these cases the large J expansion of the 3-point correlator has the same structure as expected in perturbative (tree-level and one-loop) dual gauge theory. We conjecture that, like the leading chiral primary correlator term, the coefficients of the first few subleading terms are also protected, i.e. should be the same at strong and weak coupling.

hep-th↗

arXiv2008

Accelerating Branes and Brane Temperature

We define the local acceleration and jerk of a relativistic brane in an ambient spacetime, and construct from them a dimensionless parameter lambda that must be small for an interpretation of brane acceleration as local Unruh temperature. As examples, we discuss (i) open rotating branes, for which lambda>1 (ii) closed spherical branes expanding in Minkowski spacetime, for which lambda=0 when the worldvolume is either an Einstein static universe or de Sitter space, in which case the brane temperature equals the Gibbons-Hawking temperature, (iii) closed spherical branes in anti-de Sitter spacetime, for which a maximally symmetric worldvolume is anti-de Sitter, Minkowski or de Sitter according to whether the magnitude of the brane acceleration is less than, equal to or greater than a `critical' value, and (iv) the BTZ black hole, viewed as a membrane.

hep-th↗