G. Krein - Universitaet Mainz

G. Krein
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G. Krein
Universitaet Mainz

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High Energy Physics - Phenomenology (38)
Nuclear Theory (29)
High Energy Physics - Lattice (13)
Nuclear Experiment (11)
High Energy Physics - Theory (9)
High Energy Physics - Experiment (7)
Physics - Statistical Mechanics (5)
Physics - Soft Condensed Matter (1)
Quantum Physics (1)
General Relativity and Quantum Cosmology (1)
Physics - Atomic Physics (1)
Physics - Disordered Systems and Neural Networks (1)

Publications Authored By G. Krein

$\phi$-meson--nucleus bound state energies and absorption widths are calculated for seven selected nuclei by solving the Klein-Gordon equation with complex optical potentials. Essential input for the calculations, namely the medium-modified $K$ and $\overline{K}$ meson masses, as well as the density distributions in nuclei, are obtained from the quark-meson coupling model. The attractive potential for the $\phi$-meson in the nuclear medium originates from the in-medium enhanced $K\overline{K}$ loop in the $\phi$-meson self-energy. Read More

A symmetry-preserving treatment of a vector-vector contact interaction is used to study charmed heavy-light mesons. The contact interaction is a representation of nonperturbative kernels used in Dyson-Schwinger and Bethe-Salpeter equations of QCD. The Dyson-Schwinger equation is solved for the $u,\,d,\,s$ and $c$ quark propagators and the bound-state Bethe-Salpeter amplitudes respecting spacetime-translation invariance and the Ward-Green-Takahashi identities associated with global symmetries of QCD are obtained to calculate masses and electroweak decay constants of the pseudoscalar $\pi,\,K$, $D$ and $D_s$ and vector $\rho$, $K^*$, $D^*$, and $D^*_s$ mesons. Read More

A dual representation for non-Abelian lattice gauge theories where the new set of dynamical variables belong to the natural numbers $\mathbb{N}_{0}$ is discussed. After looking at the constraints on the dual variables due to gauge symmetry, the theory for the gauge group SU(2) is solved using Monte Carlo simulations based on Prokof'ev-Svistunov worm type of algorithms. The performance of the Monte Carlo is investigated for different types of updates. Read More

The mass and decay width of the $\phi$ meson in cold nuclear matter are computed in an effective Lagrangian approach. The medium dependence of these properties are obtained by evaluating kaon-antikaon loop contributions to the $\phi$ self-energy, employing the medium-modified kaon masses, calculated using the quark-meson coupling model. The loop integral is regularized with a dipole form factor, and the sensitivity of the results to the choice of cutoff mass in the form factor is investigated. Read More

We compute the masses of the pseudoscalar mesons $\pi^+$ , $K^0$ and $D^+$ at finite temperature and baryon chemical potential. The computations are based on a symmetry- preserving Dyson-Schwinger equation treatment of a vector-vector four quark contact interaction. The results found for the temperature dependence of the meson masses are in qualitative agreement with lattice QCD data and QCD sum rules calculations. Read More

Cross sections for the charm-production reactions $\bar p p \to \bar \Lambda_c^- \Sigma_c^+$, $\bar \Sigma_c\Sigma_c$, $\bar \Xi_c\Xi_c$, and $\bar \Xi_c'\Xi_c'$ are presented, for energies near their respective thresholds. The results are based on a calculation performed in the meson-exchange framework in close analogy to earlier studies of the J\"ulich group on the strangeness-production reactions $\bar p p \to \bar \Lambda\Sigma$, $\bar \Sigma\Sigma$, $\bar \Xi\Xi$ by connecting the two sectors via SU(4) flavor symmetry. The cross sections are found to be in the order of $0. Read More

We study a three-body system, formed by a light particle and two identical heavy dipoles, in two dimensions in the Born-Oppenheimer approximation. We present the analytic light-particle wave function resulting from an attractive zero-range potential between the light and each of the heavy particles. It expresses the large-distance universal properties which must be reproduced by all realistic short-range interactions. Read More

We study the effect of a hot and dense medium on the binding energy of hadronic molecules with open-charm mesons. We focus on a recent chiral quark-model-based prediction of a molecular state in the $N \bar D$ system. We analyze how the two-body thresholds and the hadron-hadron interactions are modified when quark and meson masses and quark-meson couplings change in a function of the temperature and baryon density according to predictions of the Nambu--Jona-Lasinio model. Read More

We use a symmetry-preserving regularization method of ultraviolet divergences in a vector-vector contact interac- tion model for low-energy QCD. The contact interaction is a representation of nonperturbative kernels used Dyson-Schwinger and Bethe-Salpeter equations. The regularization method is based on a subtraction scheme that avoids standard steps in the evaluation of divergent integrals that invariably lead to symmetry violation. Read More

We show how a scheme of rewriting a divergent momentum integral can conciliate results obtained with the Nambu--Jona-Lasinio model and recent lattice results for the chiral transition in the presence of a chiral imbalance in quark matter. Purely vacuum contributions are separated from medium-dependent regularized momentum integrals in such a way that one is left with ultraviolet divergent momentum integrals that depend on vacuum quantities only. The scheme is applicable to other commonly used effective models to study quark matter with a chiral imbalance, it allows us to identify the source of their difficulties in reproducing the qualitative features of lattice results, and enhances their predictability and uses in other applications. Read More

$\Lambda^+_c$ hypernuclei are expected to have binding energies and other properties similar to those of strange hypernuclei in view of the similarity between the quark structures of the strange and charmed hyperons, namely $\Lambda(uds)$ and $\Lambda^+_c (udc)$. One striking difference however occurs in their mesonic decays, as there is almost no Pauli blocking in the nucleonic decay of a charm hypernucleus because the final-state nucleons leave the nucleus at high energies. The nuclear medium nevertheless affects the mesonic decays of charm hypernucleus because the nuclear mean fields modify the masses of the charm hyperon. Read More

The phenomenon of inverse magnetic catalysis of chiral symmetry in QCD predicted by lattice simulations can be reproduced within the Nambu--Jona-Lasinio model if the coupling~$G$ of the model decreases with the strength $B$ of the magnetic field and temperature~$T$. The thermo-magnetic dependence of $G(B,T)$ is obtained by fitting recent lattice QCD predictions for the chiral transition order parameter. Different thermodynamic quantities of magnetized quark matter evaluated with $G(B, T)$ are compared with the ones obtained at constant coupling, $G$. Read More

We highlight Hermiticity issues in bound-state equations whose kernels are subject to a highly asymmetric mass and momentum distribution and whose eigenvalue spectrum becomes complex for radially excited states. We trace back the presence of imaginary components in the eigenvalues and wave functions to truncation artifacts and suggest how they can be eliminated in the case of charmed mesons. The solutions of the gap equation in the complex plane, which play a crucial role in the analytic structure of the Bethe-Salpeter kernel, are discussed for several interaction models and qualitatively and quantitatively compared to analytic continuations by means of complex-conjugate pole models fitted to real solutions. Read More

The last few years have been witness to a proliferation of new results concerning heavy exotic hadrons. Experimentally, many new signals have been discovered that could be pointing towards the existence of tetraquarks, pentaquarks, and other exotic configurations of quarks and gluons. Theoretically, advances in lattice field theory techniques place us at the cusp of understanding complex coupled-channel phenomena, modelling grows more sophisticated, and effective field theories are being applied to an ever greater range of situations. Read More

In the framework of weakly-coupled pNRQCD, we derive, first, an analytical expression for the chromo-polarizability of $1S$-bottomonium states in agreement with previous determinations. Then we use the QCD trace anomaly to obtain the two-pion production amplitude for the chromo-polarizability operator and match the result to a chiral effective field theory with $1S$-bottomonium states and pions as degrees-of-freedom. In this chiral effective field theory we compute some long-range properties of the $1S$ bottomonium generated by the pion coupling such as the leading chiral logarithm to the $1S$-bottomonium mass and the van der Waals potential between two $1S$-bottomonium states. Read More

We have calculated the temperature dependence of shear $\eta$ and bulk $\zeta$ viscosities of quark matter due to quark-meson fluctuations. The quark thermal width originating from quantum fluctuations of quark-$\pi$ and quark-$\sigma$ loops at finite temperature is calculated with the formalism of real-time thermal field theory. Temperature-dependent constituent-quark and meson masses, and quark-meson couplings are obtained in the Nambu--Jona-Lasinio model. Read More

Having in mind its future extension for theoretical investigations related to charmed nuclei, we develop a relativistic formalism for the nonmesonic weak decay of single-$\Lambda$ hypernuclei in the framework of the independent-particle shell model and with the dynamics represented by the $(\pi,K)$ one-meson-exchange model. Numerical results for the one-nucleon-induced transition rates of ${}^{12}_{\Lambda}\textrm{C}$ are presented and compared with those obtained in the analogous nonrelativistic calculation. There is satisfactory agreement between the two approaches, and the most noteworthy difference is that the ratio $\Gamma_{n}/\Gamma_{p}$ is appreciably higher and closer to the experimental value in the relativistic calculation. Read More

The production of a $D\bar D$ meson-pair in antiproton-proton ($\bar p p$) annihilation close to the production threshold is investigated, with special emphasis on the role played by the $\psi$(3770) resonance. The study is performed in a meson-baryon model where the elementary charm production process is described by baryon exchange. Effects of the interactions in the initial and final states are taken into account rigorously, where the latter involves also those due to the $\psi$(3770). Read More

We investigate the leptonic decay constants of the pion and its excitations with a 5-d holographic model for quantum chromodynamics. We prove numerically that the leptonic decay constants of the excited states of the pion vanish in the chiral limit when chiral symmetry is dynamically broken. This nontrivial result is in agreement with a solid prediction of quantum chromodynamics and is based on a generalized Gell-Mann-Oakes-Renner relationship involving the decay constants and masses of the excited states of the pion. Read More

We perform an extensive study of the role played by the equation of state in the hydrodynamic evolution of the matter produced in relativistic heavy ion collisions. By using the same initial conditions and freeze-out scenario, the effects of different equations of state are compared by calculating their respective hydrodynamical evolution, particle spectra, harmonic flow coefficients $v_2$, $v_3$ and $v_4$ and two-pion interferometry radius parameters. The equations of state investigated contain distinct features, such as the nature of the phase transition, as well as strangeness and baryon density contents, which are expected to lead to different hydrodynamic responses. Read More

We study the production of charmed mesons (D, D_s) in antiproton-proton annihilation close to the reaction thresholds. The elementary charm production process is described by baryon exchange and in the constituent quark model, respectively. Effects of the interactions in the initial and final states are taken into account rigorously. Read More

Although asymptotic freedom is an essential feature of QCD, it is absent in effective chiral quark models like the Nambu--Jona-Lasinio and linear sigma models. In this work we advocate that asymptotic freedom plays a key role in the recently observed discrepancies between results of lattice QCD simulations and quark models regarding the behavior of the pseudocritical temperature $T_{\rm pc}$ for chiral symmetry restoration in the presence of a magnetic field $B$. We show that the lattice predictions that $T_{\rm pc}$ decreases with $B$ can be reproduced within the Nambu--Jona-Lasinio model if the coupling constant $G$ of the model decreases with $B$ and the temperature. Read More

We analyze the Markovian and non-Markovian stochastic quantization methods for a complex action quantum mechanical model analog to a Maxwell-Chern-Simons eletrodynamics in Weyl gauge. We show through analytical methods convergence to the correct equilibrium state for both methods. Introduction of a memory kernel generates a non-Markovian process which has the effect of slowing down oscillations that arise in the Langevin-time evolution toward equilibrium of complex action problems. Read More

We have evaluated the shear viscosity of pion gas taking into account its scattering with the low mass resonances, $\sigma$ and $\rho$ during propagation in the medium. The thermal width (or collisional rate) of the pions is calculated from $\pi\sigma$ and $\pi\rho$ loop diagrams using effective interactions in the real time formulation of finite temperature field theory. A very small value of shear viscosity by entropy density ratio ($\eta/s$), close to the KSS bound, is obtained which approximately matches the range of values of $\eta/s$ used by Niemi et al. Read More

Using relativistic conformal hydrodynamics coupled to the linear $\sigma$ model we study the evolution of matter created in heavy--ion collisions. We focus the study on the influence of the dynamics of the chiral fields on the charged-hadron elliptic flow $v_2$ for a temperature--independent as well as for a temperature--dependent $\eta/s$ that is calculated from kinetic theory. We find that $v_2$ is not very sensitive to the coupling of chiral fields to the hydrodynamic evolution, but the temperature dependence of $\eta/s$ plays a much bigger role on this observable. Read More

We investigate the thermodynamics of a self-interacting relativistic charged scalar field in the presence of weak disorder. We consider quenched disorder which couples linearly to the mass of the scalar field. After performing noise averages over the free energy of the system, we find that disorder increases the mean-field critical temperature for Bose-Einstein condensation at finite density. Read More

We investigate the low-energy elastic DbarN interaction using a quark model that confines color and realizes dynamical chiral symmetry breaking. The model is defined by a microscopic Hamiltonian inspired in the QCD Hamiltonian in Coulomb gauge. Constituent quark masses are obtained by solving a gap equation and baryon and meson bound-state wave functions are obtained using a variational method. Read More

Using a framework in which all elements are constrained by Dyson-Schwinger equation studies in QCD, and therefore incorporates a consistent, direct and simultaneous description of light- and heavy-quarks and the states they constitute, we analyze the accuracy of SU(4)-flavor symmetry relations between {\pi}{\rho}{\pi}, K{\rho}K and D{\rho}D couplings. Such relations are widely used in phenomenological analyses of the interactions between matter and charmed mesons. We find that whilst SU(3)-flavor symmetry is accurate to 20%, SU(4) relations underestimate the D{\rho}D coupling by a factor of five. Read More

We consider a pointlike two-level system undergoing uniformly accelerated motion. We evaluate the transition probability for a finite time interval of this system coupled to a massless scalar field near a fluctuating event horizon. Horizon fluctuations are modeled using a random noise which generates light-cone fluctuations. Read More

The $DN$ interaction is studied in close analogy to the meson-exchange $\bar KN$ potential of the Juelich group using SU(4) symmetry constraints. The model generates the $\Lambda_c$(2595) resonance dynamically as a $DN$ quasi-bound state. Results for $DN$ scattering lengths and cross sections are presented and compared with predictions based on the Weinberg-Tomozawa term. Read More

Using second--order dissipative hydrodynamics coupled self-consistently to the linear $\sigma$ model we study the 2+1 dimensional evolution of the fireball created in Au+Au relativistic collisions. We analyze the influence of the dynamics of the chiral fields on the charged-hadron elliptic flow $v_2$ and on the ratio $v_4/(v_2)^2$ for a temperature-independent as well as for a temperature-dependent viscosity-to-entropy ratio $\eta/s$ calculated from the linearized Boltzmann equation in the relaxation time approximation. We find that $v_2$ is not very sensitive to the coupling of chiral sources to the hydrodynamic evolution, but the temperature dependence of $\eta/s$ plays a much bigger role on this observable. Read More

$J/\Psi$-nuclear bound state energies are calculated for a range of nuclei by solving the Proca (Klein-Gordon) equation. Critical input for the calculations, namely the medium-modified $D$ and $D^*$ meson masses, as well as the nucleon density distributions in nuclei, are obtained from the quark-meson coupling model. The attractive potential originates from the $D$ and $D^*$ meson loops in the $J/\Psi$ self-energy in nuclear medium. Read More

A free massive scalar field in inhomogeneous random media is investigated. The coefficients of the Klein-Gordon equation are taken to be random functions of the spatial coordinates. The case of an annealed-like disordered medium, modeled by centered stationary and Gaussian processes, is analyzed. Read More

We calculate mass shift of the $J/\Psi$ meson in nuclear matter arising from the modification of $DD, DD^*$ and $D^*D^*$ meson loop contributions to the $J/\Psi$ self-energy. The estimate includes the in-medium $D$ and $D^*$ meson masses consistently. The $J/\Psi$ mass shift (scalar potential) calculated is negative (attractive), and complementary to the attractive potential obtained from the QCD color van der Waals forces. Read More

We study the production of charmed mesons (D) and baryons (Lambda_c) in antiproton-proton (app) annihilation close to their respective production thresholds. The elementary charm production process is described by either baryon/meson exchange or by quark/gluon dynamics. Effects of the interactions in the initial and final states are taken into account rigorously. Read More

A model of the DN interaction is presented which is developed in close analogy to the meson-exchange KbarN potential of the Juelich group utilizing SU(4) symmetry constraints. The main ingredients of the interaction are provided by vector meson (rho, omega) exchange and higher-order box diagrams involving D*N, D\Delta, and D*\Delta intermediate states. The coupling of DN to the pi-Lambda_c and pi-Sigma_c channels is taken into account. Read More

The $J/\Psi$ mass shift in cold nuclear matter is computed using an effective Lagrangian approach. The mass shift is computed by evaluating $D$ and $D^*$ meson loop contributions to the $J/\Psi$ self-energy employing medium-modified meson masses. The modification of the $D$ and $D^*$ masses in nuclear matter is obtained using the quark-meson coupling model. Read More

We describe an analog model for quantum gravity effects in condensed matter physics. The situation discussed is that of phonons propagating in a fluid with a random velocity wave equation. We consider that there are random fluctuations in the reciprocal of the bulk modulus of the system and study free phonons in the presence of Gaussian colored noise with zero mean. Read More

Predictions for the charm-production reaction antiproton-proton -> antiLambda_c-Lambda_c for energies near the threshold are presented. The calculations are performed in a meson-exchange framework in close analogy to our earlier study on antiproton-proton -> antiLambda-Lambda by connecting the two processes via SU(4) symmetry. The obtained antiLambda_c-Lambda_c production cross sections are in the order of 1 to 7 \mub, i. Read More

We consider the non-Markovian Langevin evolution of a dissipative dynamical system in quantum mechanics in the path integral formalism. After discussing the role of the frequency cutoff for the interaction of the system with the heat bath and the kernel and noise correlator that follow from the most common choices, we derive an analytic expansion for the exact non-Markovian dissipation kernel and the corresponding colored noise in the general case that is consistent with the fluctuation-dissipation theorem and incorporates systematically non-local corrections. We illustrate the modifications to results obtained using the traditional (Markovian) Langevin approach in the case of the exponential kernel and analyze the case of the non-Markovian Brownian motion. Read More

We perform a quark model calculation of the quarkonia $b\overline{b}$ and $c\overline{c}$ spectra using smooth and sudden string breaking potentials. The screening parameter is scale dependent and can be related to an effective running gluon mass that has a finite infrared fixed point. A temperature dependence for the screening mass is motivated by lattice QCD simulations at finite temperature. Read More

The thermodynamics of a scalar field with a quartic interaction is studied within the linear delta expansion (LDE) method. Using the imaginary-time formalism the free energy is evaluated up to second order in the LDE. The method generates nonperturbative results that are then used to obtain thermodynamic quantities like the pressure. Read More

We examine the possibility to extract information about the DN and DbarN interactions from the pbar d to D Dbar N reaction. We utilize the notion that the open-charm mesons are first produced in the annihilation of the antiproton on one nucleon in the deuteron and subsequently rescatter on the other (the spectator) nucleon. The latter process is then exploited for investigating the DN and DbarN interactions. Read More

A novel strategy to handle divergences typical of perturbative calculations is implemented for the Nambu--Jona-Lasinio model and its phenomenological consequences investigated. The central idea of the method is to avoid the critical step involved in the regularization process, namely the explicit evaluation of divergent integrals. This goal is achieved by assuming a regularization distribution in an implicit way and making use, in intermediary steps, only of very general properties of such regularization. Read More

We consider the Langevin lattice dynamics for a spontaneously broken lambda phi^4 scalar field theory where both additive and multiplicative noise terms are incorporated. The lattice renormalization for the corresponding stochastic Ginzburg-Landau-Langevin and the subtleties related to the multiplicative noise are investigated. Read More

We consider the modification of the Cahn-Hilliard equation when a time delay process through a memory function is taken into account. We then study the process of spinodal decomposition in fast phase transitions associated with a conserved order parameter. The introduced memory effect plays an important role to obtain a finite group velocity. Read More

After five years of running at RHIC, and on the eve of the LHC heavy-ion program, we highlight the status of femtoscopic measurements. We emphasize the role interferometry plays in addressing fundamental questions about the state of matter created in such collisions, and present an enumerated list of measurements, analyses and calculations that are needed to advance the field in the coming years. Read More

We investigate the dissipative real-time evolution of the order parameter for the deconfining transition in the pure SU(2) gauge theory. The approach to equilibrium after a quench to temperatures well above the critical one is described by a Langevin equation. To fix completely the markovian Langevin dynamics we choose the dissipation coefficient, that is a function of the temperature, guided by preliminary Monte Carlo simulations for various temperatures. Read More

We investigate the Dbar-N interaction at low energies using a meson-exchange model supplemented with a short-distance contribution from one-gluon-exchange. The model is developed in close analogy to the meson-exchange KN interaction of the Juelich group utilizing SU(4) symmetry constraints. The main ingredients of the interaction are provided by vector meson (rho, omega) exchange and higher-order box diagrams involving D*N, D\Delta, and D*\Delta intermediate states. Read More