arXiv subjects

G. Krein

Publications and source records attributed to G. Krein.

At least 19 recordsLinked to original sources

arXiv2026

Momentum Distribution and Contact Parameters of a mass-imbalanced three-body system across the Efimov-Unatomic transition

We investigate the single-particle momentum distribution and contact parameters of mass-imbalanced three-body systems at the critical dimension Dc, where the transition between discrete and continuous scale invariance takes place as the spatial dimension is tuned between three and two dimensions. We show that the asymptotic momentum distribution at Dc is governed by a distinct logarithmic scaling structure, which differs fundamentally from both the log-periodic behavior of Efimov states and the power-law scaling of the unatomic regime. This structure requires the introduction of an additional three-body contact parameter associated with a quadratic logarithmic contribution, leading to a finite and well-defined description of the momentum tail at the transition. This additional three-body parameter depends sensitively on the mass imbalance, changing sign across different mass configurations and vanishing for identical particles. As a consequence, the three-body contribution to the momentum distribution can be suppressed at a characteristic momentum scale, leaving the asymptotic tail entirely determined by the two-body contact. We further analyze the narrow intermediate region connecting the Efimov and unatomic regimes, here identified as an intermediate scaling regime, whose extent and properties are strongly controlled by the mass ratio. These results establish the critical dimension as a regime with emergent scaling properties and provide experimentally accessible signatures for probing the transition between discrete and continuous scale invariance in few-body quantum systems.

cond-mat.quant-gas↗

arXiv2026

Structural glasses model using disorder fields: the boson peak from local ground states

We show the emergence of a contribution characteristic of the boson peak in the spectral density of structural glasses. To model the vitreous state, we consider static density-fluctuation fields coupled to a multiplicative quenched disorder. Performing an ensemble average over all disorder realizations, a functional series representation of the average free energy is obtained. In this series representation of the average free energy for the glassy state of matter, we identify in the function space effective actions. These effective actions present a large number of metastable states and ground states. Random first-order transition, widely discussed in the literature as a description of the transition from the supercooled liquid to the glassy state of matter, emerges naturally in our formalism. We establish the connection between the use of hyperbolic differential equations with random coefficients and the presence of many ground states in the average free energy. This connection allows us to study emergent excitations in such amorphous materials.

cond-mat.dis-nn↗

arXiv2025

Open-Flavor Heavy Hadron Production in Heavy-Ion Collisions

We study the production of open-flavor heavy hadrons in relativistic heavy-ion collisions. The hadronization in the quark-gluon plasma is described in the quark coalescence model. We evaluated yields and transverse momentum distributions. A simultaneous study of conventional and exotic hadrons is carried out. The Wigner functions are evaluated using hadron wave functions obtained from a single realistic quark model. Thus, results are presented in a single framework for the production of open-flavor heavy mesons, baryons, and exotic tetraquarks, in particular: $D^{0}$, $B^{0}$, $Λ_{Q}$, $Σ_{Q}$, $Ξ_{Q}$, $Ξ_{QQ^\prime}$, and $T_{QQ^\prime}$ ($Q,Q^\prime=c$ or $b$). The consequences of a partial restoration of chiral symmetry at the hadronization temperature are studied in detail.

hep-ph↗

arXiv2025

The glue that binds us all -- Latin America and the Electron-Ion Collider

The Electron-Ion Collider, a next generation electron-hadron and electron-nuclei scattering facility, will be built at Brookhaven National Laboratory. The wealth of new data will shape research in hadron physics, from nonperturbative QCD techniques to perturbative QCD improvements and global QCD analyses, for the decades to come. With the present proposal, Latin America based physicists, whose expertise lies on the theory and phenomenology side, make the case for the past and future efforts of a growing community, working hand-in-hand towards developing theoretical tools and predictions to analyze, interpret and optimize the results that will be obtained at the EIC, unveiling the role of the glue that binds us all. This effort is along the lines of various initiatives taken in the U.S., and supported by colleagues worldwide, such as the ones by the EIC User Group which were highlighted during the Snowmass Process and the Particle Physics Project Prioritization Panel (P5).

nucl-ex↗

arXiv2025

Confinement-induced unatomic trimer states in mass-imbalanced systems

As resonantly interacting trimers of the type AAB are progressively squeezed from $D=3$ to $D=2$, unatomic states emerge. We calculated the contacts from the high momentum tail of the single particle densities. The sharp increase of the contacts serves as a signature of the transition between the Efimov and unatomic regimes, characterized by the emergence of continuous scale invariance when the system reaches a critical dimension, $D_c$. This continuous scale invariance starts to dominate the behavior of the system at the dimension $\overline{D}<D_c$, below which the trimers momentum distribution tails exhibit a power-law behavior signaling the unatomic regime. To illustrate our findings, we studied compounds of the forms $^{7}$Li$-^{23}$Na$_{2}$, $^{7}$Li$-^{87}$Rb$_{2}$ and $^{7}$Li$-^{133}$Cs$_{2}$. The increase in the mass-imbalance of the trimers reduces the interval between $D_c$ and $\overline{D}$. The emergence of unatomic states can be experimentally verified by observing the two-body contact parameter, which is a quantity directly related to the thermodynamic properties of the gas.

cond-mat.quant-gas↗

arXiv2024

Confinement-induced unatomic trimer states

The signature of an unatomic system is revealed by a continuous scale invariance that appears during a progressive dimensional squeezing of a resonantly interacting trimer. The unatomic regime is reached at the dimension $\overline D$, which for three identical atoms is found to be $\overline D=2.292$ - below this value, the trimer wave function at short distances displays a power-law behaviour. The fingerprint of this crossover is a sharp evolution of the contacts that characterizes the trimer momentum distribution tail.

cond-mat.quant-gas↗

arXiv2024

Reliability of the Born-Oppenheimer approximation in noninteger dimensions

We address the question of the reliability of the Born-Oppenheimer (BO) approximation for a mass-imbalanced resonant three-body system embedded in noninteger dimensions. We address this question within the problem of a system of currently experimental interest, namely $^7$Li$-^{87}$Rb$_2$. We compare the Efimov scale parameter as well as the wave functions obtained using the BO approximation with those obtained using the Bethe-Peierls boundary condition.

cond-mat.quant-gas↗

arXiv2024

Critical Casimir effect in a disordered $O(2)$-symmetric model

Critical Casimir effect appears when critical fluctuations of an order parameter interact with classical boundaries. We investigate this effect in the setting of a Landau-Ginzburg model with continuous symmetry in the presence of quenched disorder. The quenched free energy is written as an asymptotic series of moments of the models partition function. Our main result is that, in the presence of a strong disorder, Goldstone modes of the system contribute either with an attractive or with a repulsive force. This result was obtained using the distributional zeta-function method without relying on any particular ansatz in the functional space of the moments of the partition function.

cond-mat.soft↗

arXiv2023

Single-particle momentum distribution of Efimov states in noninteger dimensions

We studied the single-particle momentum distribution of mass-imbalanced Efimov states embedded in noninteger dimensions. The contact parameters, which can be related to the thermodynamic properties of the gas, were calculated from the high momentum tail of the single particle densities. We studied the dependence of the contact parameters with the progressive change of the noninteger dimension, ranging from three (D=3) to two (D=2) dimensions. Within this interval, we move from the (D=3) regime where the Efimov discrete scale symmetry drives the physics, until close to the critical dimension, which depends on the mass imbalance, where the continuum scale symmetry takes place. We found that the two- and three-body contacts grow significantly in magnitude with the decrease of the noninteger dimension towards the critical dimension, impacting observables of resonantly interacting trapped Bose gases.

cond-mat.quant-gas↗

arXiv2023

Analog Model for Euclidean Wormholes Effects

Using results of statistical field theory for systems with an anisotropic disorder, we present an analog model for Euclidean wormholes and topological fluctuation effects in a Riemannian space $\mathcal{M}^\mathrm{d}$. The contribution of wormholes and topological fluctuations to the Euclidean gravitational functional integral is modeled by quenched randomness defined in the $\mathbb{R}^{\mathrm{d}}$ manifold. We obtain a disorder-averaged free energy by taking the average over all the realizations of the random fields. In the scenario of topology fluctuation, there appears a superposition of infinite branes that contribute to the physical quantities. All topology fluctuations can be understood as two distinct kinds of Euclidean wormholes: wormholes confined to one brane, and wormholes connecting different branes.

hep-th↗

arXiv2022

Restoration of a Spontaneously Broken Symmetry in an Euclidean Quantum $λφ^{4}_{d+1}$ model with Quenched Disorder

We investigate the low temperature behavior of a system in a spontaneously broken symmetry phase described by an Euclidean quantum $λφ^{4}_{d+1}$ model with quenched disorder. Using a series representation for the averaged generating functional of connected correlation functions in terms of the moments of the partition function, we study the effects of the disorder linearly coupled to the scalar field. To deal with the strongly correlated disorder in imaginary time, we employthe equivalence between the model defined in a $d$-dimensional space with imaginary time with the statistical field theory model defined on a space ${\mathbb R}^{d}\times S^{1}$ with anisotropic quenched disorder. Next, using fractional derivatives and stochastic differential equations we obtain at tree-level the Fourier transform of the correlation functions of the disordered system. In one-loop approximation, we prove that there is a denumerable collection of moments of the partition function that can develop critical behavior. Below the critical temperature of the pure system, with the bulk in the ordered phase, there are a large number of critical temperatures that take each of these moments from an ordered to a disordered phase. We show the emergence of generic scale invariance in the system.

hep-th↗

arXiv2022

Disorder Effects in Dynamical Restoration of Spontaneously Broken Continuous Symmetry

We discuss the Euclidean quantum $O(N)$ model with $N=2$ in a continuous broken symmetry phase. We study the system at low temperatures in the presence of quenched disorder linearly coupled to the scalar field. Performing an average over the ensemble of all realizations of the disorder, we represent the average free energy in terms of a series of the moments of the partition function. In the one-loop approximation, we prove that there is a denumerable collection of moments that lead the system to develop critical behavior. Our results indicate that in an equilibrium system, the strongly correlation of the disorder in imaginary produces generic scale invariance in the massive modes.

hep-th↗

arXiv2021

Hidden charm mesons in nuclear matter and nuclei

Recent results for the $η_c$- and $J/ψ$-nucleus bound state energies for various nuclei are presented. The attractive potentials for the $η_c$ and $J/ψ$ mesons in the nuclear medium originate, respectively, from the in-medium enhanced $DD^{*}$ and $D\bar{D}$ loops in the $η_c$ and $J/ψ$ self energies. Our results suggest that the $η_c$ and $J/ψ$ mesons should form bound states with all the nuclei considered.

nucl-th↗

arXiv2021

Charmonium in nuclear matter and nuclei

We present results for the $η_c$-nucleus bound state energies for various nuclei using an effective Lagrangians approach. The attractive potentials for the $η_c$ in the nuclear medium originate from the medium-modified intermediate $D D^{*}$ state in the $η_c$ self energy, using the local density approximation. Our results suggest that the $η_c$ should form bound states with all the nuclei considered

nucl-th↗

arXiv2021

Comment on "$Λ_c N$ interaction in leading order covariant chiral effective field theory"

Song et al. [Phys. Rev. C 102, 065208 (2020)] presented results for the $Λ_c N$ interaction based on an extrapolation of lattice simulations by the HAL QCD Collaboration at unphysical quark masses to the physical point via covariant chiral effective field theory. We point out that their predictions for the $^3D_1$ partial wave disagree with available lattice results. We discuss the origin of that disagreement and present a comparison with predictions from conventional (non-relativistic) chiral effective field theory.

nucl-th↗

arXiv2020

Femtoscopy of the Origin of the Nucleon Mass

We study the prospects of using femtoscopic low-momentum correlation measurements at the Large Hadron Collider to access properties of the J/psi-nucleon interaction. The QCD multipole expansion in terms of the J/psi chromopolarizability relates the forward scattering amplitude to a key matrix element to the origin of the nucleon mass problem, the average chromoelectric gluon distribution in the nucleon. We use information on the J/psi-nucleon interaction provided by lattice QCD simulations and phenomenological models to compute J/psi-nucleon correlation functions. The computed correlation functions show clear sensitivity to the interaction, in particular to the J/psi chromopolarizability.

hep-ph↗

arXiv2020

$η_{c}$-nucleus bound states

$η_c$-nucleus bound state energies are calculated for various nuclei. Essential input for the calculations, namely the medium-modified $D$ and $D^{*}$ meson masses, as well as the density distributions in nuclei, are calculated within the quark-meson coupling (QMC) model. The attractive potentials for the $η_c$ meson in the nuclear medium originate from the in-medium enhanced $DD^{*}$ loops in the $η_c$ self-energy. Our results suggest that the $η_c$ meson should form bound states with all the nuclei considered.

hep-ph↗

arXiv2020

Femtoscopic correlations and the $Λ_c N$ interaction

We study the prospects for deducing constraints on the interaction of charmed baryons with nucleons from measurements of two-particle momentum correlation functions for $Λ_c p$. The correlation functions are calculated for $Λ_c N$ and $Σ_c N$ interactions that have been extrapolated from lattice QCD simulations at unphysical masses of $m_π=410-570$ MeV to the physical point using chiral effective field theory as guideline. In addition, we consider phenomenological $Y_c N$ models from the literature to explore the sensitivity of the results to the properties of the interaction in detail. We find that a measurement of the $Λ_c p$ correlation functions could indeed allow one to discriminate between strongly attractive $Λ_c N$ forces, as predicted by some phenomenological models, and a weakly attractive interaction as suggested by the presently available lattice simulations.

nucl-th↗