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M. Asakawa

Publications and source records attributed to M. Asakawa.

32 records · Page 2Linked to original sources
arXiv2001

Maximum Entropy Analysis of the Spectral Functions in Lattice QCD

First principle calculation of the QCD spectral functions (SPFs) based on the lattice QCD simulations is reviewed. Special emphasis is placed on the Bayesian inference theory and the Maximum Entropy Method (MEM), which is a useful tool to extract SPFs from the imaginary-time correlation functions numerically obtained by the Monte Carlo method. Three important aspects of MEM are (i) it does not require a priori assumptions or parametrizations of SPFs, (ii) for given data, a unique solution is obtained if it exists, and (iii) the statistical significance of the solution can be quantitatively analyzed. The ability of MEM is explicitly demonstrated by using mock data as well as lattice QCD data. When applied to lattice data, MEM correctly reproduces the low-energy resonances and shows the existence of high-energy continuum in hadronic correlation functions. This opens up various possibilities for studying hadronic properties in QCD beyond the conventional way of analyzing the lattice data. Future problems to be studied by MEM in lattice QCD are also summarized.

hep-lat↗
arXiv1999

Spectral Functions of Hadrons in Lattice QCD

Using the maximum entropy method, spectral functions of the pseudo-scalar and vector mesons are extracted from lattice Monte Carlo data of the imaginary time Green's functions. The resonance and continuum structures as well as the ground state peaks are successfully obtained. Error analysis of the resultant spectral functions is also given on the basis of the Bayes probability theory.

hep-lat↗
arXiv1999

Hadronic Spectral Functions in Lattice QCD

QCD spectral functions of hadrons in the pseudo-scalar and vector channels are extracted from lattice Monte Carlo data of the imaginary time Green's functions. The maximum entropy method works well for this purpose, and the resonance and continuum structures in the spectra are obtained in addition to the ground state peaks.

hep-lat↗
arXiv1999

Back-to-Back Correlations for Bosons Modified by Medium

Novel back-to-back correlations are shown to arise for thermal ensembles of squeezed bosonic states associated with medium-modified mass-shifts. The strength of these correlations could become unexpectedly large in heavy ion collisions.

nucl-th↗
arXiv1998

Anomaly Induced Domain Formation of Disoriented Chiral Condensates

We discuss the effect of chiral anomaly as a possible mechanism for triggering formation of domains of disoriented chiral condensate (DCC) in relativistic heavy ion collisions. The anomalous $π^0 \to 2 γ$ coupling and the strong, Lorentz contracted electromagnetic fields of the heavy ions combine to produce the ``anomaly kick'' to the field configuration of the neutral pion field. We implement the effect of anomaly kick in our numerical simulation of the linear sigma model in a schematic way which preserves its characteristic features: the effect is coherent over a large region of space but is opposite in sign above and below the ion scattering plane. We demonstrate by detailed simulations with longitudinal expansion that the DCC domain formation is dramatically enhanced by the anomaly kick in spite of its small absolute magnitude. We examine the behavior of various physical quantities such as pion fields, the axial vector currents, and their correlation functions. Our results also provide useful insight into the mechanism and properties of DCC domain formation, in general. Finally, we discuss some experimental observables which can signal the anomaly induced formation of DCC.

hep-ph↗
arXiv1998

Non-Central Heavy-Ion Collisions are the Place to Look for DCC

We give two reasons why we believe that non-central ultrarelativistic heavy ion collisions are the place to look for the disoriented chiral condensates (DCC). First, we argue that the most probable quench scenario for the formation of DCC requires non-central collisions. Second, we show by numerical simulations that strong electromagnetic fields of heavy ions can exert a surprisingly large effect on the DCC domain formation through the chiral anomaly. The effect again requires non-central collisions. Interestingly, the result of simulations is consistent with the formation of correlated two domains of the chiral condensate, which are aligned in space, perpendicular to the scattering plane, but misaligned in isospin space.

nucl-th↗
arXiv1997

Two-mode squeezed states in high energy physics

We discuss the possibility to observe hadron modification in hot and dense matter via the correlation of identical particles. We find that a modification of hadronic masses in medium leads to two-mode squeezing which signals itself in a back-to-back correlations of hadrons. This effect leads to a signal of a shift of $ϕ$-meson mass.

quant-ph↗
arXiv1997

Quantum-Statistical Correlations and Single Particle Distributions for Slowly Expanding Systems with Temperature Profile

Competition among particle evaporation, temperature gradient and flow is investigated in a phenomenological manner, based on a simultaneous analysis of quantum statistical correlations and momentum distributions for a non-relativistic, spherically symmetric, three-dimensionally expanding, finite source. The parameters of the model emission function are constrained by fits to neutron and proton momentum distributions and correlation functions in intermediate energy heavy-ion collisions. The temperature gradient is related to the momentum dependence of the radius parameters of the two-particle correlation function, as well as to the momentum-dependent temperature parameter of the single particle spectrum, while a long duration of particle evaporation is found to be responsible for the low relative momentum behavior of the two-particle correlations.

nucl-th↗
arXiv1995

What Thermodynamics tells about QCD Plasma near Phase Transition

Due to a rapid change of the entropy density $s(T)$ across the critical temperature $T_c$ of the QCD phase transition, the pressure $P(T)$ and the energy density $e(T)$ above $T_c$ generally deviate from their Stefan-Boltzmann values. We shall demonstrate this both analytically and numerically for a general class of $s(T)$ consistent with thermodynamical constraints and make a qualitative comparison of the result with the lattice QCD data. Quantities related to $ds(T)/dT$ such as the specific heat and sound velocity are also discussed.

hep-ph↗
arXiv1994

Secondary phi meson peak as an indicator of QCD phase transition in ultrarelativistic heavy ion collisions

In a previous paper, we have shown that a double phi peak structure appears in the dilepton invariant mass spectrum if a first order QCD phase transition occurs in ultrarelativistic heavy ion collisions. Furthermore, the transition temperature can be determined from the transverse momentum distribution of the low mass phi peak. In this work, we extend the study to the case that a smooth crossover occurs in the quark-gluon plasma to the hadronic matter transition. We find that the double phi peak structure still exists in the dilepton spectrum and thus remains a viable signal for the formation of the quark-gluon plasma in ultrarelativistic heavy ion collisions.

nucl-th↗
arXiv1994

Seeing the QCD phase transition with phi mesons

A double phi peak structure in the dilepton invariant mass spectrum from ultrarelativistic heavy ion collisions is proposed as a signal for the phase transition from the quark-gluon plasma to the hadronic matter. The low mass phi peak results from the decay of phi mesons with reduced in-medium mass during the transition. Furthermore, the measurement of the transverse momentum distribution of these low mass phi mesons offers a viable means for determining the temperature of the phase transition.

nucl-th↗