arXiv subjects

Javier G. Subils

Publications and source records attributed to Javier G. Subils.

At least 19 recordsLinked to original sources

arXiv2026

Complexity measures in holographic cascading theories with multiscale dynamics

Using the gravitational duals, we perform a systematic study of two notions of complexity in a family of three-dimensional gauge theories with rich infrared structure. For thermofield double states, we employ the complexity=volume prescription, which relates computational complexity to the volume of the dual Einstein-Rosen bridge. For one particle states created by the insertion of a local operator on the vacuum, we study their spreading in Krylov space, encoded holographically by the radial momentum of bulk excitations. We investigate these two notions of complexity across the parameter space of the theories, focusing on the two limiting values of a tunable parameter. Near the limit where the theories flow close to an intermediate conformal fixed point, both notions reveal distinct manifestations of ``walking'' dynamics. Near the opposite limit, computational complexity is largely insensitive to the confining nature of the ground state, whereas the frequency of oscillations in the Krylov spread complexity -- set by the emerging infrared scale -- is sensitive to the presence of confinement.

hep-th↗

arXiv2026

Microscopic Description of Critical Bubbles

First-order phase transitions occur through the nucleation of critical bubbles of the stable phase within the metastable phase. Using holography, we present a fully microscopic description of these bubbles in a strongly coupled, four-dimensional gauge theory at finite temperature. In the gravitational dual, these bubbles correspond to static, inhomogeneous and unstable black-brane solutions with a localized deformation on the horizon. We construct these solutions across the entire metastable branch and compute the surface tension and the nucleation rate. We then compare these microscopic results with those obtained from a two-derivative effective action for the order parameter in two different scenarios. When the effective action is derived from the microscopic theory via holography, we find remarkable agreement. However, when the effective action is constrained only by the equation of state and dimensional analysis, significant discrepancies emerge. These discrepancies can be resolved if an additional constraint related to the surface tension is imposed.

hep-th↗

arXiv2025

Spontaneous breaking of baryon symmetry in strongly coupled three-dimensional theories

We show that baryon number symmetry is spontaneously broken in a class of three-dimensional, ${\cal N}=1$ supersymmetric theories with a discrete mass spectrum. These models serve as lower-dimensional, less-supersymmetric analogs of the Klebanov-Strassler solution, sharing properties such as the presence of a cascade. The spontaneous symmetry breaking is evidenced by the appearance of a Goldstone mode, which corresponds to a vector fluctuation in the gravity dual.

hep-th↗

arXiv2025

On entanglement c-functions in confining gauge field theories

Entanglement entropy has proven to be a powerful tool for probing renormalization group (RG) flows in quantum field theories, with c-functions derived from it serving as candidate measures of the effective number of degrees of freedom. While the monotonicity of such c-functions is well established in many settings, notable exceptions occur in theories with a mass scale. In this work, we investigate entanglement c-functions in the context of holographic RG flows, with a particular focus on flows across dimensions induced by circle compactifications. We argue that in spacetime dimensions $d \geq 4$, standard constructions of c-functions, which rely on higher derivatives of the entanglement entropy of either a ball or a cylinder, generically lead to non-monotonic behavior. Working with known dual geometries, we argue that the non-monotonicity stems not from any pathology or curvature singularity, but from a transition in the holographic Ryu--Takayanagi surface. In compactifications from four to three dimensions, we propose a modified construction that restores monotonicity in the infrared, although a fully monotonic ultraviolet extension remains elusive. Furthermore, motivated by entanglement entropy inequalities, we conjecture a bound on the cylinder entanglement c-function, which holds in all our examples.

hep-th↗

arXiv2025

Light dilaton near critical points in top-down holography

We study a class of UV-complete, strongly coupled, confining three-dimensional field theories, that exhibit a novel stabilisation mechanism for the mass of the lightest scalar composite state, relying on the existence of a critical point. The theories admit a holographic dual description in terms of regular backgrounds in eleven-dimensional supergravity. Their phase diagram includes a line of first-order phase transitions ending at the critical point, where the transition becomes of second order. We calculate the mass spectrum of bound states of the field theory, by considering fluctuations around the background solutions, and find that, near the critical point, a hierarchy of scales develops, such that one state becomes parametrically light. We identify this state as the dilaton, the pseudo-Nambu-Goldstone boson associated with the spontaneous breaking of approximate scale invariance. This stabilisation mechanism might be exploited to address hierarchy problems in particle and astroparticle physics.

hep-th↗

arXiv2024

Cosmic censorship in a (dual) collider

We investigate cosmic censorship in anti-de Sitter space in holographic models in which the ground state is described by a good singularity. These include supersymmetric truncations of string/M-theory, for which a positive-energy theorem holds. At the boundary, our solutions describe a boost-invariant fluid in which the temperature decreases monotonically with time. On the gravity side, they correspond to black-brane spacetimes with a receding horizon. In classical gravity, curvature invariants at the horizon grow without bound. In the full theory this regime may or may not be reached. In some cases it is avoided by a phase transition to a regular geometry. In others it is reached but the boundary hydrodynamic evolution can be continued, provided the equation of state at parametrically small energies is known. Both cases require the inclusion of finite-$N$ or finite-coupling effects.

hep-th↗

arXiv2024

Light holographic dilatons near critical points

We investigate the relation between the emergence of a dilaton in gapped (confining) field theories, and the presence of either complex fixed points or instabilities in the strongly coupled dynamics in two classes of bottom-up holographic models. We demonstrate that in one of the two classes there is a critical line of first-order phase transitions (at zero temperature) that terminates at a critical point. We calculate the mass spectrum of fluctuations of the associated regular gravity backgrounds, which we interpret as bound states in the dual field theories. In proximity to the second-order phase transition, we find a parametrically light scalar state, and its composition leads us to identify it as a dilaton.

hep-th↗

arXiv2023

Limitations of entanglement entropy in detecting thermal phase transitions

We explore the efficacy of entanglement entropy as a tool for detecting thermal phase transitions in a family of gauge theories described holographically. The rich phase diagram of these theories encompasses first and second-order phase transitions, as well as a critical and a triple point. While entanglement measures demonstrate some success in probing transitions between plasma phases, they prove inadequate when applied to phase transitions leading to gapped phases. Nonetheless, entanglement measures excel in accurately determining the critical exponent associated with the observed phase transitions, providing valuable insight into the critical behavior of these systems.

hep-th↗

arXiv2023

Baryonic matter at strong coupling: confining superfluids and deconfined ferromagnets

We study the phase diagram of a strongly coupled confining theory in $2+1$ dimensions, as a function of temperature and baryon chemical potential. The theory has a fully fledged supergravity holographic dual, that we use to predict a line of first order phase transitions separating a confining phase and a deconfined phase. Both phases exhibit a non-zero baryon density thus providing a first example of baryonic matter in a confining string dual that does not require the introduction of flavor branes. We argue that the confining phase is a baryon superfluid, while the deconfined phase has non-zero baryon magnetization.

hep-th↗

arXiv2023

Primordial Black Hole Formation during a Strongly Coupled Crossover

The final mass distribution of primordial black holes is sensitive to the equation of state of the Universe at the scales accessible by the power spectrum. Motivated by the presence of phase transitions in several beyond the Standard Model theories, some of which are strongly coupled, we analyze the production of primordial black holes during such phase transitions, which we model using the gauge/gravity duality. We focus in the (often regarded as physically uninteresting) case for which the phase transition is just a smooth crossover. We find an enhancement of primordial black hole production in the range $M_{\rm{PBH}}\in[10^{-16},10^{-6}]M_{\odot}$.

astro-ph.CO↗

arXiv2022

Monopoles and confinement in three dimensions from holography

We study the phase diagram of a confining three-dimensional $\mathcal{N}=1$ supersymmetric $\text{U}(N)\times\text{U}(N+M)$ theory with holographic dual corresponding to a known string theory solution. The theory possesses a global $\text{U}(1)$ symmetry under which magnetic monopoles are charged. We introduce both temperature and an external magnetic field for monopoles and find that there are deconfinement phase transitions as any of the two is increased, supporting monopole condensation as the possible mechanism for confinement. We find that the transition as the magnetic field is increased is second order, providing the first example in holographic duals of a deconfinement transition which is not first order. We also uncover a rich structure in the phase diagram, with a triple point and a critical point where a line of first order transitions end.

hep-th↗

arXiv2022

Boost-invariant superfluid flows

We present some exact solutions to the ideal hydrodynamics of a relativistic superfluid with an almost-conformal equation of state. The solutions have stress tensors which are invariant under Lorentz boosts in one direction, and represent superfluid generalisations of the Bjorken and Gubser flows. We also study corrections to the flows in first-order hydrodynamics, arguing that dissipation is dominated by the shear viscosity. We present some simple numerical solutions for these viscous corrections. Finally, we estimate the size of corrections to the flows arising when the spontaneously broken $\mathrm{U}(1)$ symmetry responsible for superfluidity is only approximate, giving the corresponding Goldstone boson a small non-zero mass. We find that the massless solutions can still provide good approximations at sufficiently small spatial rapidities.

hep-th↗

arXiv2021

Holographic approach to transport in dense QCD matter

The transport properties of dense QCD matter play a crucial role in the physics of neutron stars and their mergers, but are notoriously difficult to study with traditional quantum field theory tools. Specializing to the case of unpaired quark matter in beta equilibrium, we approach the problem through the machinery of holography, in particular the V-QCD and D3-D7 models, and derive results for the electrical and thermal conductivities and the shear and bulk viscosities. In addition we compare the bulk to shear viscosity ratio to the speed of sound and find that it violates the so-called Buchel bound. Our results differ dramatically from earlier predictions of perturbative QCD, the root causes and implications of which we analyze in detail.

hep-th↗

arXiv2021

Non-perturbative Aspects of Quantum Field Theories from Holography

In this thesis we investigate some aspects of quantum field theories from a holographic perspective. In the first chapters we examine in detail a one-paremeter family of three-dimensional gauge theories by means of their type IIA gravity duals. We analyse features such as their confinement nature, spectrum, entanglement properties or thermal phase transitions. This family interpolates between quasi-conformal and quasi-confining physics. In the last two chapters, we use bottom-up models to study complex conformal field theories and transport properties of dense QCD respectively.

hep-th↗

arXiv2021

Multiple Mass Hierarchies from Complex Fixed Point Collisions

A pair of complex-conjugate fixed points that lie close to the real axis generates a large mass hierarchy in the real renormalization group flow that passes in between them. We show that pairs of complex fixed points that are close to the real axis and to one another generate multiple hierarchies, some of which can be parametrically enhanced. We illustrate this effect at weak coupling with field-theory examples, and at strong coupling using holography. We also construct complex flows between complex fixed points, including flows that violate the $c$-theorem.

hep-th↗

arXiv2020

Transport in strongly coupled quark matter

Motivated by the possible presence of deconfined quark matter in neutron stars and their mergers and the important role of transport phenomena in these systems, we perform the first-ever systematic study of different viscosities and conductivities of dense quark matter using the gauge/gravity duality. Utilizing the V-QCD model, we arrive at results that are in qualitative disagreement with the predictions of perturbation theory, which highlights the differing transport properties of the system at weak and strong coupling and calls for caution in the use of the perturbative results in neutron-star applications.

hep-th↗

arXiv2020

Is entanglement a probe of confinement?

We study various entanglement measures in a one-parameter family of three-dimensional, strongly coupled Yang-Mills-Chern-Simons field theories by means of their dual supergravity descriptions. A generic field theory in this family possesses a mass gap but does not have a linear quark-antiquark potential. For the two limiting values of the parameter, the theories flow either to a fixed point or to a confining vacuum in the infrared. We show that entanglement measures are unable to discriminate confining theories from non-confining ones with a mass gap. This lends support on the idea that the phase transition of entanglement entropy at large-N can be caused just by the presence of a sizable scale in a theory and just by itself should not be taken as a signal of confinement. We also examine flows passing close to a fixed point at intermediate energy scales and find that the holographic entanglement entropy, the mutual information, and the F-functions for strips and disks quantitatively match the conformal values for a range of energies.

hep-th↗

arXiv2020

Holographic Complex Conformal Field Theories

The loss of criticality in the form of weak first-order transitions or the end of the conformal window in gauge theories can be described as the merging of two fixed points that move to complex values of the couplings. When the complex fixed points are close to the real axis, the system typically exhibits walking behavior with Miransky (or Berezinsky-Kosterlitz-Thouless) scaling. We present a novel realization of these phenomena at strong coupling by means of the gauge/gravity duality, and give evidence for the conjectured existence of complex conformal field theories at the fixed points.

hep-th↗