arXiv subjects

Alexander Soloviev

Publications and source records attributed to Alexander Soloviev.

At least 19 recordsLinked to original sources

arXiv2026

Imaging non-hydrodynamic modes with jet wakes

While studies of ultra-relativistic heavy-ion collisions have established that the quark--gluon plasma exhibits hydrodynamic behavior, direct signatures of non-hydrodynamic modes have remained elusive, and no observable is known to be exclusively sensitive to them. Here, we show that the angular structure of the jet wake provides such a probe. In the long-wavelength limit, hydrodynamics contributes only to the lowest angular moments of the detector image of the jet wake, while higher moments directly encode microscopic non-equilibrium dynamics. The jet wake thus serves as a spectroscopic probe of the medium's non-hydrodynamic sector. We develop a general kinetic-theory framework relating the angular moments of the late-time energy flux generated by a jet to the relaxation spectrum of the collision operator. In all models considered, non-hydrodynamic modes leave distinct imprints on the higher angular moments. Our results motivate precision measurements of the higher angular moments of the negative jet wake.

hep-ph↗

arXiv2026

Four-channel prototype using coherent combining of ultrashort laser pulses for dipole configuration approximation

This paper presents a four-channel prototype system for the geometric combining and coherent addition of tightly focused femtosecond laser radiation into a standing-wave field configuration. A stabilization system for beam pointing and relative phase of the four optical channels has been implemented, and its performance has been experimentally demonstrated. To characterize the standing-wave electromagnetic field distribution at the main focus of the system, an original measurement technique based on a fiber subwavelength optical probe has been employed. This work has been conducted in support of the exawatt-scale XCELS project.

physics.optics↗

arXiv2026

Asymptotics of superfluid Bjorken flow

We consider the dynamics of an expanding superfluid modeled by Mueller-Israel-Stewart theory coupled to a complex scalar field with a $U(1)$ symmetry that is spontaneously broken. This is a manageable theoretical setting for explorations of the chiral phase transition of expanding quark-gluon plasma. We study the late proper-time behavior of Bjorken flow in this physical system and find that asymptotic solutions can be expressed as a transseries of a novel form, which contains factors like $\tau^{-a\ln \tau}$. This transseries describes how the information encoded in the initial data is diluted in the course of dissipative evolution. These solutions retain memory of the symmetry-breaking transition and describe two qualitatively different late-time behaviors of the dynamical variables, depending on condensate relaxation rate: either a purely damped fall-off or damped oscillations. The possibility that such oscillations could be imprinted in the observed outcomes of heavy ion collision experiments is the main physical insight that follows from our analysis.

hep-th↗

arXiv2026

Spin hydrodynamics on a hyperbolic expanding background

We study relativistic spin hydrodynamics on the hyperbolic $\kappa=-1$ flow background recently identified by Grozdanov. This background corresponds to an $SO(2,1)$-invariant, transversely expanding solution with finite spacetime support in Minkowski space, in contrast to the well-known Gubser flow $(\kappa=+1)$ which possesses $SO(3)$ symmetry and infinite transverse extent. Working within the formulation of perfect-fluid spin hydrodynamics, we derive the exact evolution equations for all spin components of the spin potential on the $\kappa=-1$ background. We find that the enhanced early-time expansion rate and the presence of a causal edge lead to a stronger localization of spin dynamics compared to the Gubser case. Remarkably, the azimuthal component of the spin potential oscillates as it decays in the forward lightcone, in stark contrast to the Gubser flow. Thus, our results establish the $\kappa=-1$ flow as a distinct and physically meaningful benchmark for studying spin dynamics in expanding relativistic fluids with finite spacetime support.

nucl-th↗

arXiv2025

On prethermal time crystals from semi-holography

We demonstrate the existence of a pair of almost dissipationless oscillating modes at low temperatures in both the shear and sound channels of a hybrid quantum system, comprised of a weakly self-interacting perturbative sector coupled to strongly self-interacting holographic degrees of freedom described by a black hole geometry. We argue that these modes realize prethermal time-crystal behavior in semi-holographic systems without fine-tuning and can be observed by measuring operators that probe either the hard (perturbative) or the soft (holographic) sector. We also find novel {short wavelength} instabilities that lead to the formation of inhomogeneities even at higher temperatures. These results provide evidence that black holes with planar horizons and dynamical boundary conditions can develop both inhomogeneous and metastable time-crystal phases over a wide range of temperatures set by an intermediate scale given by the intersector coupling. Furthermore, they suggest that such phases can be realized without external driving in non-Abelian plasmas of asymptotically free gauge theories in the large-$N$ limit.

hep-th↗

arXiv2025

Relativistic superfluid profiles near critical surfaces

Landau's two-fluid model of superfluidity ceases to apply in regions where the condensate amplitude exhibits rapid spatial variation, such as vortex cores or in the vicinity of container walls. A recently proposed relativistic Gross-Pitaevskii-type framework treats the condensate as an independent scalar degree of freedom, enabling a controlled analysis of such regimes. We use it to construct stationary superflows close to the superfluid-normal phase boundary, and examine their stability. We obtain an exact expression for Landau's critical velocity and show that the standard Newtonian profiles (such as the near-vortex condensate depletion or the boundary-layer decay) persist unmodified in the relativistic setting. We further analyse a genuinely relativistic configuration in which an accelerated superfluid develops a phase boundary induced by Tolman temperature gradients.

nucl-th↗

arXiv2025

Close encounters with attractors of the third kind

We report on the existence of a hydrodynamic attractor in the Mueller-Israel-Stewart framework of a fluid living in the novel geometry discovered recently by Grozdanov. This geometry, corresponding to a hyperbolic slicing of dS$_3\times\mathbb{R}$, complements previous analyses of attractors in Bjorken (flat slicing) and Gubser (spherical slicing) flows. The fluid behaves like a sharply localized droplet propagating rapidly along the lightcone. Typical solutions approach the hydrodynamic attractor rapidly at late times despite a Knudsen number exceeding unity, suggesting that the inverse Reynolds number captures hydrodynamization more faithfully since the shear stress vanishes at late times. This is in stark contrast to Gubser flow, which has both the Knudsen and inverse Reynolds number becoming small for intermediate times. We close with a comparison to Weyl-transformed Bjorken flow and discuss possible phenomenological applications.

hep-th↗

arXiv2025

The probe limit in MHD and its implications for magnetic transport

Many phenomenological and effective field-theoretical (EFT) applications of magnetohydrodynamics (MHD) in the presence of a background magnetic field employ a simplifying assumption whereby the electromagnetic and the energy-momentum fluctuations decouple. In studies of magnetic transport, for example in magnetic diffusion, the conservation of energy and momentum is then neglected. In this paper, we investigate the details and the consistency of this so-called $\textit{probe limit}$ in different parametric regimes of MHD plasmas. In the first part of the paper, our discussion explores the hydrodynamic (higher-form) theory of MHD. In the second part, we then explicitly test the probe limit by using a microscopic holographic (AdS/CFT) model of a strongly coupled plasma. In the process, we develop the holographic Schwinger-Keldysh EFT prescription for describing the bulk 2-form fields and their dual 1-form symmetries. Moreover, we find evidence of a phase transition at low temperatures and show that magnetic Hall transport can emerge as a consequence of background charge density that breaks the charge conjugation symmetry of the state. Finally, we discuss the implications for magnetic transport, with a particular view towards the dynamics of dense nuclear matter in neutron stars.

hep-th↗

arXiv2025

Hybrid thermalization in the large $N$ limit

Semi-holography provides a formulation of dynamics in gauge theories involving both weakly self-interacting (perturbative) and strongly self-interacting (non-perturbative) degrees of freedom. These two subsectors interact via their effective metrics and sources, while the full local energy-momentum tensor is conserved in the physical background metric. In the large $N$ limit, the subsectors have their individual entropy currents, and so the full system can reach a pseudo-equilibrium state in which each subsector has a different physical temperature. We first complete the proof that the global thermal equilibrium state, where both subsectors have the \textit{same} physical temperature, can be defined in consistency with the principles of thermodynamics and statistical mechanics. Particularly, we show that the global equilibrium state is the unique state with maximum entropy in the microcanonical ensemble. Furthermore, we show that in the large $N$ limit, a \textit{typical} non-equilibrium state of the full isolated system relaxes to the global equilibrium state when the average energy density is large compared to the scale set by the inter-system coupling. We discuss quantum statistical perspectives.

hep-th↗

arXiv2025

Relaxation for massive particles: transport and causality

Correlators at finite density and temperature encode important information about a physical system, such as transport and causality. For a massive gas of particles in the relaxation time approximation of kinetic theory, we provide complete analytic results for all first order transport coefficients, including thermoelectric coefficients. We demonstrate the first complete picture of the complex structure of the correlators as a function of mass, providing an interpretation in terms of the causal structure of lightcones. We provide a simple criterion to extract the effective lightcone velocity from the cut of the retarded correlator.

hep-th↗

arXiv2025

Quenching through the QCD chiral phase transition

We present a detailed numerical and analytical study of the out-of-equilibrium dynamics of Model G, the dynamical universality class relevant to the chiral phase transition. We perform numerical 3D stochastic (Langevin) simulations of the $O(4)$ critical point for large lattices in the chiral limit. We quench the system from the high-temperature unbroken phase to the broken phase and study the non-equilibrium dynamics of pion fields. Strikingly, the non-equilibrium evolution of the two-point functions exhibits a regime of growth, a parametrically large enhancement, and a subsequent slow relaxation to equilibrium. We analyze our numerical results using dynamic critical scaling and mean-field theory. The growth of the two point functions is determined by the non-linear dynamics of an ideal non-abelian superfluid, which is a limit of Model G that reflects the broken chiral symmetry. We also relate the non-equilibrium two-point functions to a long-lived parametric enhancement of soft pion yields relative to thermal equilibrium following a quench.

hep-lat↗

arXiv2025

Supercooled Goldstone Bosons at the QCD Chiral Phase Transition

We discuss a universal non-equilibrium enhancement of long-wavelength Goldstone bosons induced by quenches to the broken phase in Model G -- the dynamical universality class of an $O(4)$-antiferromagnet and the chiral phase transition in QCD. Scaling arguments for the coarsening dynamics describing the formation of the chiral condensate predict a parametric enhancement in the infrared spectra of Goldstones, a prediction confirmed by stochastic simulations of the transition. The details of the enhancement are determined by the non-linear dynamics of a superfluid effective theory, which is a limit of Model G reflecting the broken $O(4)$ symmetry. Our results translate to a parametric enhancement of low-momentum pions in heavy-ion collisions at the LHC, which are underpredicted in current hydrodynamic models without critical dynamics.

hep-ph↗

arXiv2024

Towards the BBGKY hierarchy: a scheme beyond the Boltzmann equation and application to a weakly confined QCD gas

In classical kinetic theory, the BBGKY hierarchy is an infinite chain of integro-differential equations that describes the full time-reversal-invariant (Liouville) system of interacting (quasi)-particles in terms of $N$-particle distribution functions. In this work, instead of truncating the hierarchy at the lowest level, as is done by the Boltzmann equation, we develop a scheme similar to the relaxation time approximation that is in principle able to account for the entire chain of equations. We then explicitly investigate its truncation at the second level of the BBGKY hierarchy and, within this scheme, study the spectra of conserved operator correlation functions in a gas of weakly confined hadrons. We also discuss how these higher levels account for parts of the operator spectra `deeper in the ultra-violet regime' and compare them to known results derived from the holographic duality.

hep-th↗

arXiv2024

Superfluids in expanding backgrounds and attractor times

We determine the behavior of an out-of-equilibrium superfluid, composed of a $U(1)$ Goldstone mode coupled to hydrodynamic modes in a M\" uller-Israel-Stewart theory, in expanding backgrounds relevant to heavy ion collision experiments and cosmology. For suitable initial conditions, the evolution of the hydrodynamic variables leads to a change in the potential of the Goldstone mode, spontaneously breaking the symmetry. After some time, the condensate becomes small, leading the system evolution to be well described via hydrodynamic attractors for a timescale that we determine in Bjorken and Gubser flows. We define this new timescale as the \textit{attractor time} and show its dependence on initial conditions. In the case of the Gubser flow, we provide for the first time a complete description of the nonlinear evolution of the system, including a novel nonlinear regime of constant anisotropy not found in the Bjorken evolution. Finally, we consider the superfluid in the dynamical FLRW (Friedmann-Lemaitre-Roberston-Walker) background, where we observe a similar attractor behavior, dependent on the initial conditions, that at late times approaches a regime dominated by the condensate.

hep-ph↗

arXiv2024

Holographic Gubser flow: A combined analytic and numerical study

Gubser flow is an evolution with cylindrical and boost symmetries, which can be best studied by mapping the future wedge of Minkowski space (R$^{3,1}$) to dS$_3$ $\times$ $\mathbb{R}$ in a conformal relativistic theory. Here, we sharpen our previous analytic results and validate them via the first numerical exploration of the Gubser flow in a holographic conformal field theory. Remarkably, the leading generic behavior at large de Sitter time is free-streaming in transverse directions and the sub-leading behavior is that of a color glass condensate. We also show that Gubser flow can be smoothly glued to the vacuum outside the future Minkowski wedge generically given that the energy density vanishes faster than any power when extrapolated to early proper time or to large distances from the central axis. We find that at intermediate times the ratio of both the transverse and longitudinal pressures to the energy density converge approximately to a fixed point which is hydrodynamic only for large initial energy densities. We argue that our results suggest that the Gubser flow is better applied to collective behavior in jets rather than the full medium in the phenomenology of heavy ion collisions and can reveal new clues to the mechanism of confinement.

hep-th↗

arXiv2024

Analytic structure of diffusive correlation functions

Diffusion is a dissipative transport phenomenon ubiquitously present in nature. Its details can now be analysed with modern effective field theory (EFT) techniques that use the closed-time-path (or Schwinger-Keldysh) formalism. We discuss the structure of the diffusive effective action appropriate for the analysis of stochastic or thermal loop effects, responsible for the so-called long-time tails, to all orders. We also elucidate and prove a number of properties of the EFT and use the theory to establish the analytic structure of the $n$-loop contributions to diffusive retarded two-point functions. Our analysis confirms a previously proposed result by Delacr\'{e}taz that used microscopic conformal field theory arguments. Then, we analyse a number of implications of these loop corrections to the dispersion relations of the diffusive mode and new, gapped modes that appear when the EFT is treated as exact. Finally, we discuss certain features of an all-loop model of diffusion that only retains a special subset of $n$-loop `banana' diagrams.

hep-th↗

arXiv2024

Spectra of correlators in the relaxation time approximation of kinetic theory

The relaxation time approximation (RTA) of the kinetic Boltzmann equation is likely the simplest window into the microscopic properties of collective real-time transport. Within this framework, we analytically compute all retarded two-point Green's functions of the energy-momentum tensor and a conserved $U(1)$ current in thermal states with classical massless particles (a `CFT') at non-zero density, and in the absence and presence of broken translational symmetry. This is done in $2+1$ and $3+1$ dimensions. RTA allows a full explicit analysis of the analytic structure of different correlators (poles versus branch cuts) and the transport properties that they imply (the thermoelectric conductivities, and the hydrodynamic, quasihydrodynamic and gapped mode dispersion relations). Our inherently weakly coupled analysis thereby also enables a direct comparison with previously known strongly coupled results in holographic CFTs dual to the Einstein-Maxwell-axion theories.

hep-th↗

arXiv2023

How Gubser flow ends in a holographic conformal theory

Gubser flow is an axis-symmetric and boost-invariant evolution in a relativistic quantum field theory which is best studied by mapping $\mathbf{R}^{3,1}$ to $dS_{3}\times \mathbf{R}$ when the field theory has conformal symmetry. We show that at late de-Sitter time, which corresponds to large proper time and central region of the future wedge within $\mathbf{R}^{3,1}$, the holographic conformal field theory plasma can reach a state in which $\varepsilon = P_T = - P_L$, with $\varepsilon$, $P_T$ and $P_L$ being the energy density, transverse and longitudinal pressures, respectively. We further determine the full sub-leading behaviour of the energy-momentum tensor at late time. Restricting to flows in which the energy density decays at large transverse distance from the central axis in $\mathbf{R}^{3,1}$, we show that this decay should be faster than any power law. Furthermore, in this case the energy density also vanishes in $\mathbf{R}^{3,1}$ faster than any power as we go back to early proper time. Hydrodynamic behavior can appear in intermediate time.

hep-th↗