One flavor mass reweighting in lattice QCD

One flavor mass reweighting can be used in lattice QCD computations to fine tune the quark masses to their physical values. We present a new method that utilizes an unbiased stochastic estimation of the one flavor determinant. The stochastic estimation is based on the integral representation of the determinant of a complex matrix, which we prove. In contrast to other methods it can also be applied in situations where the determinant has a complex phase. The stochastic error is controlled by determinant factorizations based on mass interpolation and Schur decomposition. As an example of an application we demonstrate how the method can be used to tune the up–down quark mass difference.     

Vector boson production in pPb and PbPb collisions at the LHC and its impact on <Emphasis FontCategory="NonProportional">nCTEQ15</Emphasis> PDFs

We provide a comprehensive comparison of \(W^\pm / Z\) vector boson production data in pPb and PbPb collisions at the LHC with predictions obtained using the nCTEQ15 PDFs. We identify the measurements which have the largest potential impact on the PDFs, and estimate the effect of including these data using a Bayesian reweighting method. We find this data set can provide information as regards both the nuclear corrections and the heavy flavor (strange quark) PDF components. As for the proton, the parton flavor determination/separation is dependent on nuclear corrections (from heavy target DIS, for example), this information can also help improve the proton PDFs.     

Effects of Density-Dependent Quark Mass on Phase Diagram of Color-Flavor-Locked Quark Matter

Considering the density dependence of quark mass, we investigate the phase transition between the (unpaired) strange quark matter and the color-flavor-locked matter, which are supposed to be two candidates for the ground state of strongly interacting matter. We find that if the current mass of strange quark ms is small, the strange quark matter remains stable unless the baryon density is very high. If ms is large, the phase transition from the strange quark matter to the color-flavor-locked matter in particular to its gapless phase is found to be different from the results predicted by previous works. A complicated phase diagram of three-flavor quark matter is presented, in which the color-flavor-locked phase region is suppressed for moderate densities.     

On the problem of singular charge density at the center of pion

We generalize and analyze the expression for the quark density of a pion with allowance for the quantum nature of the impact parameter in a region of small phase space volume. As a result, there is no singularity at the center of a pion.     

Two-flavor quark matter in the perturbation theory with full thermodynamic consistency

Direct extrapolation of the strong interaction between quarks in pure perturbative calculation has a problem of thermodynamic inconsistency.A new term determined by thermodynamic consistency requirement could resolve it.This new term plays an important role at lower density in describing the equation of state of quark matter,while it is negligible at high density.Accordingly,the density behavior of the sound velocity becomes more reasonable,and the maximum mass of quark stars can be as large as two times the solar mass.     

色味连锁夸克物质中的涡旋

夸克物质在不同的温度和重子数密度下表现出丰富的相结构。高密低温情况下,夸克物质的基态是色味连锁相。介绍了金兹堡-朗道理论以及色味连锁夸克物质中的各种涡旋态（特别是准超流涡旋）,并讨论了磁场和自转对准超流涡旋的的影响。由于致密星核心内部有可能形成准超流涡旋,这一结果对致密星体的研究具有现实意义。如果将温度、夸克质量等因素考虑在内,研究夸克物质中涡旋结构的性质将为诸如致密星物理实验等相关的领域提供新的视角。The quark matter exhibits a rich phase structure at different temperatures and baryon number densities. At high baryon density and low temperature, the color-flavor locked phase is believed to be the ground state of the quark matter. We present an introduction to various vortices in the color-flavor locked quark matter, especially for the semi-superfluid vortices, and their research method (Ginzburg-Landau method). The influence of magnetic field and rotation on properties of these vortices is discussed. Due to the possibility of forming a semi-superfluid vortex in the core of the dense star, this result is of practical significance in the study of dense stars. If considering other factors, such as temperature and quark mass, study of the vortex structure properties in the quark matter could provide new perspectives for related fields, for instance dense star physics.     

QCD phase diagram according to the center group

We study an effective theory for QCD at finite temperature and density which contains the leading center symmetric and center symmetry breaking terms. The effective theory is studied in a flux representation where the complex phase problem is absent and the model becomes accessible to Monte Carlo techniques also at finite chemical potential. We simulate the system by using a generalized Prokof'ev-Svistunov worm algorithm and compare the results to a low temperature expansion. The phase diagram is determined as a function of temperature, chemical potential, and quark mass. The shape and quark mass dependence of the phase boundaries are as expected for QCD. The transition into the deconfined phase is smooth throughout, without any discontinuities or critical points.     

Quark potential in a quark–meson plasma

We investigate the effect of the restoration of chiral symmetry on the quark potential in a quark–meson plasma by considering meson exchanges in the two flavor Nambu–Jona-Lasinio model at finite temperature and density. There are two possible oscillations in the chiral restoration phase; one is the Friedel oscillation due to the sharp quark Fermi surface at high density, and the other is the Yukawa oscillation driven by the complex meson poles at high temperature. The quark–meson plasma is strongly coupled in the temperature region 1≤T/T _c≤3, with T _c being the critical temperature of the chiral phase transition. The maximum coupling in this region is located at the phase transition point.     

Molecular dynamics simulation for the baryon-quark phase transition at finite baryon density

We study the baryon-quark phase transition in the molecular dynamics (MD) of the quark degrees of freedom at finite baryon density. The baryon state at low baryon density, and the deconfined quark state at high baryon density are reproduced. We investigate the equations of state of matters with different u-d-s compositions. It is found that the baryon-quark transition is sensitive to the quark width.     

Properties of hadron and quark matter studied with molecular dynamics

We study the hadron-quark phase transition in a molecular dynamics (MD) of quark degrees of freedom. The hadron state at low density and temperature, and the deconfined quark state at high density and temperature are observed in our model. We investigate the equations of state and draw the phase diagram at wide baryon density and temperature range. We also discuss the transport property, e.g. viscosity, of $q\bar q$ matter. It is found that the ratio of the shear viscosity to the entropy density is less than one for quark matter.     

Color degrees of freedom in a quark-glue plasma at finite baryon density

We derive the color-singlet partition function for a quark-glue plasma with finite quark (baryon number) density by a projection method. Due to colorlessness there is a gradual “freezing” (reduction) of internal degrees of freedom as compared to the Stefan-Boltzmann limit. We find here that this non-perturbative effect is reduced by a finite quark density. A relation between the requirement of colorlessness of all physical states and QCD is proposed.     

Chiral restoration transition in scaled effective Lagrangians

We make a systematic study of the chiral restoration transition in function of the two free parameters of two scaled effective NJL Lagrangians. We show that it is not possible to reproduce with the same set of parameters the temperature behaviours of the quark condensate and of the quark entropy and a critical density at least equal to the normal density of nuclear systems.     

Strange star surface: a crust with nuggets

We reexamine the surface composition of strange stars. Strange quark stars are hypothetical compact stars which could exist if strange quark matter was absolutely stable. It is widely accepted that they are characterized by an enormous density gradient (10(26) g/cm4) and large electric fields at the surface. By investigating the possibility of realizing a heterogeneous crust, comprised of nuggets of strange quark matter embedded in an uniform electron background, we find that the strange star surface has a much reduced density gradient and negligible electric field. We comment on how our findings will impact various proposed observable signatures for strange stars.     

Warped unification, proton stability, and dark matter

We show that solving the problem of baryon-number violation in nonsupersymmetric grand unified theories (GUT's) in warped higher-dimensional spacetime can lead to a stable Kaluza-Klein particle. This exotic particle has gauge quantum numbers of a right-handed neutrino, but carries fractional baryon number and is related to the top quark within the higher-dimensional GUT. A combination of baryon number and SU(3) color ensures its stability. Its relic density can easily be of the right value for masses in the 10 GeV-few TeV range. An exciting aspect of these models is that the entire parameter space will be tested at near future dark matter direct detection experiments. Other exotic GUT partners of the top quark are also light and can be produced at high energy colliders with distinctive signatures.     

Neutrino emissivities in 2SC color-superconducting quark matter

The phase structure and equation of state for two-flavor quark matter under compact star constraints is studied within a nonlocal chiral quark model. Chiral symmetry breaking leads to rather large, density dependent quark masses at the phase transition to quark matter. The influence of diquark pairing gaps and quark masses on density dependent emissivities for the direct URCA is discussed. Since m _u > m _d , the direct URCA process due to quark masses cannot occur. We present cooling curves for model quark stars and discuss their relation to observational data. The text was submitted by the author in English.     

Multicanonical chain-growth algorithm

We present a temperature-independent Monte Carlo method for the determination of the density of states of lattice proteins that combines the fast ground-state search strategy of the new pruned-enriched Rosenbluth chain-growth method and multicanonical reweighting for sampling the complete energy space. Since the density of states contains all energetic information of a statistical system, we can directly calculate the mean energy, specific heat, Helmholtz free energy, and entropy for all temperatures. We apply this method to lattice proteins consisting of hydrophobic and polar monomers, and for the examples of sequences considered, we identify the transitions between native, globule, and random coil states. Since no special properties of heteropolymers are involved in this algorithm, the method applies to polymer models as well.     

色味连锁物质的稳定态及其相变

简要介绍和评述了色味连锁物质的稳定态及其相变,指出高密强相互作用物质由于夸克配对出现了一些奇异相。重点介绍色味连锁（CFL）物质及其中的Goldstone-mode凝聚现象。在考虑奇异数对应化学势μs≠0的情况下,CFL物质中K^0和K^-0都可能发生凝聚。随着重子数密度的增高,强作用物质呈现出丰富相结构,在核物质相与CFL相之间可能存在其它相,但最简单的可能相变过程是直接从核物质相变为CFL物质。这种相变可有两种过程,即两相间仅存在一个极小界面或出现两相混合区域。另外还重点讨论了K^-介子凝聚对相变的影响。Quark matter at high density has a rich phase structure. Goidstone-mode may condense in the color-flavor-locked （CFL） phase matter. We review the stability of CFL phase and its phase transition, as well as the effect of nonzero strangeness chemical potential on the CFL phase of dense quark matter. It is pointed out that, depending on the value of μs, both K^0 and K^-0 may condense in the CFL matter. As a function of quark chemical potential, other phases may intervene between the nuclear-matter and CFL phase. The simplest possibility, however, is a transition between nuclear and CFL matter. Such a transition could occur either at a single sharp interface or through a mixed phase region. The effect of discontinuous K^- meson condensation on the phase transition is also discussed. [     

New contributions to heavy quark sum rules

We analyze new contributions to the theoretical input in heavy quark sum rules and we show that the general theory of singularities of perturbation theory amplitudes yields the method to handle these specific features. In particular we study the inclusion of heavy quark radiation by light quarks at and of non-symmetric correlators at . Closely related with this is that we also propose a solution to the construction of moments of the spectral densities at where the presence of massless contributions invalidates the standard approach. We circumvent this problem through a new definition of the moments, providing an infrared safe and consistent procedure. Received: 11 February 2002 / Revised version: 14 March 2002 / Published online: 22 May 2002     

Charmed baryons in quantum chromodynamics

We consider a three-phase model of strongly interacting matter, treating each phase as an ideal gas modified by a simple phenomenological interaction feature. For nuclear matter, we take into account the baryonic repulsion; for the quark-gluon plasma, we include the bag pressure; the constituent quark phase has a non-zero effective quark mass as well as an independent bag pressure. By studying which phase dominates thermodynamically in what region of temperature and baryon number density, we obtain a phase diagram for strongly interacting matter and gain some insight on the relation between deconfinement and chiral symmetry restoration.