η string formation in QCD chiral phase transition

In the paper we discuss the role of the axial U（1）A symmetry in the chiral phase transition using the U（Nf）R × U（Nf）L linear sigma model with two massless quark flavors. It is expected that above a certain temperature the axial U（1）A symmetry will be restored. A string-like static solution, the η string can be formed and detected in the ultrarelativistic heavy-ion collision process.     

η string formation in QCD chiral phase transition

In the paper we discuss the role of the axial U(1)A symmetry in the chiral phase transition using the U(Nf)R×U(Nf)L linear sigma model with two massless quark flavors.It is expected that above a certain temperature the axial U(1)A symmetry will be restored.A string-like static solution,the η string can be formed and detected in the ultrarelativistic heavy-ion collision process.     

Chiral susceptibility and chiral phase transition in Nambu–Jona-Lasinio model

We give a general relation between the chiral susceptibility and the thermodynamical potential and a relation between the chiral susceptibility and the condition for furcations to appear in the Wigner solution(s) in the Nambu–Jona-Lasinio (NJL) model. We find that the chiral susceptibility is a quantity able to represent the appearance of furcation in the solution(s) of the gap equation and the concavo–convexity of the thermodynamical potential in the NJL model. It indicates that the chiral susceptibility can identify the stability of the states and the chiral phase transition in NJL model. We propose that analyzing the chiral susceptibility may play an important role in studying the chiral phase transition in approaches superior to the NJL model.     

Can a strong magnetic background modify the nature of the chiral transition in QCD?

The presence of a strong magnetic background can modify the nature and the dynamics of the chiral phase transition at finite temperature: for high enough magnetic fields, comparable to the ones expected to be created in noncentral high-energy heavy ion collisions at RHIC and the LHC, the original crossover is turned into a first-order transition. We illustrate this effect within the linear sigma model with quarks to one loop in the scheme for N_f=2.     

On the evaluation of gluon condensate effects in the holographic approach to QCD

In holographic QCD the effects of gluonic condensate can be encoded in a suitable deformation of the 5D metric. We develop two different methods for the evaluation of first order perturbative corrections to masses and decay constants of vector resonances in 5D Hard-Wall models of QCD due to small deformations of the metric. They are extracted either from a novel compact form for the first order correction to the vector two-point function, or from perturbation theory for vector bound-state eigenfunctions: the equivalence of the two methods is shown. Our procedures are then applied to flat and to AdS 5D Hard-Wall models; we complement results of existing literature evaluating the corrections to vector decay constant and to two-pion–one-vector couplings: this is particularly relevant to satisfy the sum rules. We concentrate our attention on the effects for the Gasser–Leutwyler coefficients; we show that as in the Chiral Quark model, the addition of the gluonic condensate improves the consistency, the understanding and the agreement with phenomenology of the holographic model.     

On the ferroelectric phase transition in polytypes of β-TlInS2 crystals

Permittivity measurements and x-ray diffraction study were performed for polytypes c and 2c of β-TlInS₂ crystals in the temperature range T = 160–250 K. Substantial differences are revealed in the temperature, sequence, and character of the structural phase transitions associated with the formation of incommensurate modulated structures and the occurrence of a ferroelectric state in these polytypes.     

Critical behavior of J/ψ across the phase transition from QCD sum rules

We study behavior of J/ψ in hot gluonic matter using QCD sum rules. Taking into account temperature dependences of the gluon condensates extracted from lattice thermodynamics for the pure SU(3) system, we find that the mass and width of J/ψ exhibit rapid change across the critical temperature.     

Accessing directly the properties of fundamental scalars in the confinement and Higgs phase

The properties of elementary particles are encoded in their respective propagators and interaction vertices. For a SU(2) gauge theory coupled to a doublet of fundamental complex scalars these propagators are determined in both the Higgs phase and the confinement phase and compared to the Yang–Mills case, using lattice gauge theory. Since the propagators are gauge dependent, this is done in the Landau limit of the ’t Hooft gauge, permitting to also determine the ghost propagator. It is found that neither the gauge boson nor the scalar differ qualitatively in the different cases. In particular, the gauge boson acquires a screening mass, and the scalar’s screening mass is larger than the renormalized mass. Only the ghost propagator shows a significant change. Furthermore, indications are found that the consequences of the residual non-perturbative gauge freedom due to Gribov copies could be different in the confinement and the Higgs phase.     

Detecting a first-order transition in the QCD phase diagram with baryon–baryon correlations

We suggest baryon–baryon correlations as an experimentally accessible signature for a first-order phase transition between a baryon-rich phase, like quarkyonic, and a baryon-suppressed hadronic phase in the QCD phase diagram. We examine the consequences of baryon-rich bubble formation in an expanding medium and show how the two-particle correlations vary in the transverse and longitudinal direction depending on the strength of the radial flow, the bubble temperature, and the time when the baryons are emitted.     

Heavy-to-light transition form factors and their relations in light-cone QCD sum rules

The light-cone QCD sum rules approach improved by using the chiral current correlator is systematically reviewed and applied to the calculation of all the heavy-to-light form factors, including all the semileptonic and penguin ones. By choosing suitable chiral currents, the light-cone sum rules for all the form factors are greatly simplified and depend mainly on one leading-twist distribution amplitude of the light meson. As a result, relations between these form factors arise naturally. At the considered accuracy, these relations reproduce the results obtained in the literature. Moreover, since the explicit dependence on the leading-twist distribution amplitudes is preserved, these relations may be more useful to simulate the experimental data and extract information on the distribution amplitude.     

On the nature of the phase transition triggered by vortex-like defects in the 2D Ginzburg–Landau model

The two-dimensional lattice Ginzburg–Landau Hamiltonian is simulated numerically for different values of the coherence length ξ in units of the lattice spacing a, a parameter which controls amplitude fluctuations. The phase diagram on the plane T–ξ is measured. Amplitude fluctuations change dramatically the nature of the phase transition: for values of ξ/a≃1, instead of the smooth Kosterlitz–Thouless transition there is a first-order transition with a discontinuity in the vortex density v and a sharper drop in the helicity modulus Γ. Both observables v and Γ are analyzed in detail at the crossover region between first and second order which occurs for intermediate values of ξ/a.     

The meaning of the terms “phase” and “phase transition”

Various meanings of the terms phase and phase transition encountered in scientific literature are discussed. These terms supplement each other and cover only together all the macroscopic situations which are now denoted by this term.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 67–71, August, 1988.     

Quantum phase transition of the Jaynes-Cummings model

Herein, we propose an experimentally feasible scheme to show the quantum phase transition of the Jaynes-Cummings(JC) model by modulating the transition frequency of a two-level system in a quantum Rabi model with strong coupling. By tuning the modulation frequency and amplitude, the ratio of the effective coupling strength of the rotating terms to the effective cavity(atomic transition) frequency can enter the deep-strong coupling regime, while the counter-rotating terms can be neglected. Thus, ...     

On the applicability of finite order perturbative QCD calculations of jet rates ine + e − annihilation

We have studied the measurement of α _s using exact second order QCD matrix element calculations of jet rates ine ⁺ e ^?→hadrons. We investigate the dependence of α _s (M _Z ² ), measured by experiments at theZ ⁰ resonance, on the choice of renormalisation scale in terms of the functional form of the three-jet matrix element. We find that only a restricted domain of the jet resolution parametery _c , $\Lambda _{\overline {MS} } $ , and scale gives a perturbation series which is well-behaved to second order, and that this domain is different for the various jet algorithms in current use.     

On the Weak Measurement of Velocity in Bohmian Mechanics

In a recent article (Wiseman in New J. Phys. 9:165, 2007), Wiseman has proposed the use of so-called weak measurements for the determination of the velocity of a quantum particle at a given position, and has shown that according to quantum mechanics the result of such a procedure is the Bohmian velocity of the particle. Although Bohmian mechanics is empirically equivalent to variants based on velocity formulas different from the Bohmian one, and although it has been proven that the velocity in Bohmian mechanics is not measurable, we argue here for the somewhat paradoxical conclusion that Wiseman’s weak measurement procedure indeed constitutes a genuine measurement of velocity in Bohmian mechanics. We reconcile the apparent contradictions and elaborate on some of the different senses of measurement at play here.     

On Δβ and the search for asymptotic scaling in lattice gauge theory

An ansatz for the β-function of SU(3) lattice gauge theory in four dimensions whose parameters are determined by Monte Carlo data is used both to compare different sets of data for Δβ and to study systematic errors. The data for Δβ obtained from different values of the block-spin renormalization group scaling factor are shown to be compatible within statistical errors. However the data is easily consistent with sizeable deviations (ca. 30% or more) from the two-loop approximation to the renormalization group scaling formula for physical quantities in the region of coupling for which Δβ essentially takes on its asymptotic value.