The spontaneous generation of magnetic and chromomagnetic fields at high temperature in the standard model

The spontaneous generation of magnetic and chromomagnetic fields at high temperature is investigated in the standard model. The consistent effective potential including the one-loop and the daisy diagrams of all boson and fermion fields is calculated. The mixing of the generated fields due to the quark loop diagram is studied in detail. It is found that the quark contribution increases the magnetic and chromomagnetic field strengths as compared with the separate generation of fields. The magnetized vacuum state is stable due to the magnetic gauge field masses included in the daisy diagrams. Some applications of the results obtained are discussed. Received: 25 October 2001 / Published online: 26 July 2002     

Meson screening masses at high temperature in quenched QCD with improved Wilson Quarks

We report on a lattice investigation of improved quenched Wilson fermions above and below the confinement-deconfinement phase transition. Results on meson screening masses as well as spatial wave functions are presented. Moreover, the meson dispersion relation is studied. Below the critical temperature we do not observe any significant temperature effect while above the data are consistent with a leading free quark behavior. Received: 2 April 2001 / Published online: 8 June 2001     

Phase transition of NaGaO2 at high pressure and high temperature

This work presents a comprehensive study on phase transition in NaGaO₂ under high pressure and temperature (P–T) conditions. X-ray diffraction (XRD) was used to identify the phase composition of the recovered samples. Our results revealed that NaGaO₂ could undergo a structural phase transition from orthorhombic $\beta$- NaGaO₂ to hexagonal $\alpha$- NaGaO₂ under high pressure and temperature. The pressure–temperature phase boundaries of NaGaO₂ were determined up to 5 GPa and 2073 K. The hexagonal $\alpha$- NaGaO₂ sample recovered from higher pressure and temperature exhibited a highly (003) preferred orientation. Besides, a reversible transition from $\alpha$- to $\beta$- NaGaO₂ was observed above 473 K under normal-pressure condition. The high-pressure melting curve of NaGaO₂, for the first time, was measured by using in-situ thermal measurement.     

Chiral symmtry of Wilson fermions at finite temperature

Chiral properties of Wilson fermions at finite temperature are investigated by numerical methods. We show that when the quark mass is properly defined, for a given β and K (hopping parameter), its value is independent of whether the system is in the high-temperature phase or in the low-temperature phase. The temperature dependence of the pion screening mass at the chiral limit where the quark mass vanishes is consistent with the physical picture that the spontaneously broken chiral symmetry is recovered at T = T_c.     

Phase diagram of aqueous solution at high pressure and low temperature

Abstract

This paper presents a constant mass high pressure isothermal calorimeter and describes the range of applications that this type of equipment can deal with. As an example, the thermophysical properties of an aqueous solution of MgSO₄ at low temperature and at high pressure have been investigated. The main results showed that the phase change heat of the solution decreased with increasing pressure and the phase change temperature of the eutectic concentration was depressed under high pressure. Those changes could be related to the MgSO₄ solubility and to water latent heat changes.     

Dimensional reduction of the two Higgs doublet model at high temperature

Dimensional reduction and effective field theory methods are applied to the Two Higgs Doublet Model at finite temperature. A sequence of two effective three-dimensional field theories which are valid on successively longer distance scales is constructed. The resulting Lagrangian can be used to study different aspects of the phase transition in this model as well as the sphaleron rate immediately after the phase transition. Received: 14 March 1999 / Published online: 22 October 1999     

Theq-state Potts model in the standard Pirogov-Sinai theory: Surface tensions and Wilson loops

Theq-state Potts model (both scalar and gauge versions) is rewritten, with the help of the duality transformation, into a form of the Pirogov-Sinai theory with noninteracting contours that can be controlled by cluster expansions onceq is large enough. This is then used in a new proof of the existence of a unique transition (inverse) temperature _t , where the mean internal energy is discontinuous. Moreover, we prove for the scalar model (again forq large enough) that there are discontinuities at _t of the magnetization and of the mass gap, with the magnetization vanishing below _t and the mass gap vanishing above _t . We also show that the surface tensions between ordered stable phases are strictly positive up to _t , and the surface tension between an ordered phase and the disordered one is strictly positive at _t . For the three-dimensional gauge model, the Wilson parameter exhibits a direct transition from an area law decay (quark confinement) to a perimeter law decay (deconfinement).On leave from ENS Rabat, Morocco.     

Fermionic dispersion relations at finite temperature and non-vanishing chemical potentials in the minimal standard model

We calculate the fermionic dispersion relations in the minimal standard model at finite temperature in presence of non-vanishing chemical potentials due to the CP-asymmetric fermionic background. The dispersion relations are calculated for a vacuum expectation value of the Higgs field equal to zero (unbroken electroweak symmetry). The calculation is performed in the real time formalism of the thermal field theory at one-loop order in a general ζ gauge. The fermionic self-energy is calculated at leading order in temperature and chemical potential and this fact permits us to obtain gauge-invariant analytical expressions for the dispersion relations.     

Wilson line correlator in the MV model: relating the glasma to deep inelastic scattering

In the color glass condensate framework the saturation scale measured in deep inelastic scattering of high energy hadrons and nuclei can be determined from the correlator of Wilson lines in the hadron wavefunction. These same Wilson lines give the initial condition of the classical field computation of the initial gluon multiplicity and energy density in a heavy ion collision. In this paper the Wilson line correlator in both adjoint and fundamental representations is computed using exactly the same numerical procedure as has been used to calculate gluon production in a heavy ion collision. In particular the discretization of the longitudinal coordinate has a large numerical effect on the relation between the color charge density parameter g²μ and the saturation scale Q_s. Our result for this relation is Q_s≈0.6g²μ, which results in the classical Yang–Mills value for the “gluon liberation coefficient” c≈1.1. PACS  24.85.+p; 25.75.-q; 13.60.Hb     

Phase transitions of sulfur at high pressure: Influence of temperature and pressure environment

Abstract

Phase transitions of orthorhombic sulfur were investigated above 10 GPa by Raman spectroscopy using red light excitation. Transitions into several phases that have been reported in previous studies using green light excitation, are confirmed. The phase behaviour is observed to depend strongly on the preparation method. In the presence of a pressure transmitting medium (methanol/ethanol, 4:1), a sequence of phases α-S₈ → [intermediate phase (“ip”) + S₆] → [S₆ + high pressure-low temperature phase (“hplt”)] is described and characterized. Without the use of a pressure transmitting medium, the phase sequence α-S₈ → [“ip” + “hplt”] + “hplt” is observed. In addition, contributions of amorphous sulfur are detected around 10 GPa, i.e. at pressures below the transformation of α-S₈ into the above-mentioned phases. Characteristic Raman spectra of the different phases are extracted and documented over a wide pressure range.