X. N. Maintas

Tachyon field quantization and Hawking radiation.

We quantize the tachyon field in a static two dimensional dilaton gravity black hole background,and we calculate the Hawking radiation rate. We find that the thermal radiation flux, due to the tachyon field, is larger than the conformal matter one. We also find that massive scalar fields which do not couple to the dilaton, do not give any contribution to the thermal radiation, up to terms quadratic in the scalar curvature.

Time-dependent perturbations in two-dimensional String Black Holes

Abstract We discuss time-dependent perturbations (induced by matter fields) of a black-hole background in tree-level two-dimensional string theory. We analyse the linearized case and show the possibility of having black-hole solutions with time-dependent horizons. The latter exist only in the presence of time-dependent “tachyon” matter fields, which constitute the only propagating degrees of freedom in two-dimensional string theory. For real tachyon field configurations it is not possible to obtaine solutions with horizons shrinking to a point. On the other hand, such a possibility seems to be realized in the case of string black-hole models formulated on higher world-sheet genera. We connect this latter result with black-hole evaporation/decay at a quantum level.

Multiscale perturbative approach toSU(2)-Higgs classical dynamics: Stability of nonlinear plane waves and bounds of the Higgs field mass

We study the classical dynamics of SU(2)-Higgs field theory using multiple scale perturbation theory. In the spontaneously broken phase, assuming small perturbations of the Higgs field around its vacuum expectation value, we derive a nonlinear Schroedinger equation and study the stability of its nonlinear plane wave solutions. The latter, turn out to be stable only if the Higgs amplitude is an order of magnitude smaller than that of the gauge field. In this case, the Higgs field mass possesses some bounds which may be relevant to the search for the Higgs particle at ongoing experiments.

A non-abelian quasi-particle model for gluon plasma

Abstract We propose a quasi-particle model for the thermodynamic description of the gluon plasma which takes into account non-abelian characteristics of the gluonic field. This is accomplished utilizing massive non-linear plane wave solutions of the classical equations of motion with a variable mass parameter, reflecting the scale invariance of the Yang–Mills Lagrangian. For the statistical description of the gluon plasma we interpret these non-linear waves as quasi-particles with a temperature dependent mass distribution. Quasi-Gaussian distributions with a common variance but different temperature dependent mean masses for the longitudinal and transverse modes are employed. We use recent Lattice results to fix the mean transverse and longitudinal masses while the variance is fitted to the equation of state of pure S U ( 3 ) on the Lattice. Thus, our model succeeds to obtain both a consistent description of the gluon plasma energy density as well as a correct behavior of the mass parameters near the critical point.

KAHLER INVARIANCE OF N=1 QUANTUM SUPERGRAVITY

Abstract The Kahler invariance of the N = 1 supergravity theory is investigated beyond the classical level. In the popular gauge fixing condition emμ−eμm=0, γμψμ=0, ∂μ(√g gμν) = 0 one has a manifestly Kahler invariant theory at the quantum level and for that the form of the path integral measure is important. We show that Fujikawas measure is consistent with quantum Kahler invariance. The integration of the auxiliary fields of the closed algebra theory brings down local determinants ( det G zz ∗ ) − necessary for maintaining the Kahler symmetry at the quantum level. Owing to the gauge independence of the path integral measure Kahler invariance is a gauge independent property.

Partonic transverse momenta in non-relativistic hyper-central quark potential models

We investigate the impact of three-body forces on the transverse-momentum distribution of partons inside the proton. This is achieved by considering the three-body problem in a class of hyper-central quark potential models. Solving the corresponding Schrödinger equation, we determine the quark wave function in the proton and with appropriate transformations and projections we find the transverse-momentum distribution of a single quark. In each case the parameters of the quark potentials are adjusted in order to sufficiently describe observable properties of the proton. Using a factorization ansatz, we incorporate the obtained transverse-momentum distribution in a perturbative QCD scheme for the calculation of the cross-section for prompt photon production in pp collisions. A large set of experimental data is fitted using as a single free parameter the mean partonic transverse momentum. The dependence of 〈kT〉 on the collision characteristics (initial energy and transverse momentum of the final photon) is much smoother when compared with similar results found in the literature using a Gaussian distribution for the partonic transverse momenta. Within the considered class of hyper-central quark potentials the one with the weaker dependence on the hyper-radius is preferred for the description of the data since it leads to the smoothest mean partonic transverse-momentum profile. We have repeated all the calculations using a two-body potential of the same form as the optimal (within the considered class) hyper-central potential in order to check if the presence of three-body forces is supported by the experimental data. Our analysis indicates that three-body forces influence significantly the form of the parton transverse-momentum distribution and consequently lead to an improved description of the considered data.