Modern Physics Letters A

We discuss ultracompact stellar objects which have multiple necks in their optical geometry. There are in fact physically reasonable equations of state for which the number of necks can be arbitrarily large. The proofs of these statements rely on a recent regularized formulation of the field equations for static spherically symmetric models due to Nilsson and Uggla. We discuss in particular the equation of state p = ρ - ρ_s which plays a central role in this context.

In the usual and current understanding of planar gauge choices for Abelian and non-Abelian gauge fields, the external defining vector n_μ can either be space-like (n² < 0) or time-like (n²>0) but not light-like (n²=0). In this work we propose a light-like planar gauge that consists of defining a modified gauge-fixing term, ℒ_GF, whose main characteristic is a two-degree violation of Lorentz covariance arising from the fact that four-dimensional space–time spanned entirely by null vectors as basis necessitates two light-like vectors, namely n_μ and its dual m_μ, with n²=m²=0, n·m≠0, say, e.g. normalized to n·m=2.

Once massless quadratically divergent tadpole diagrams are discarded, because they contain no intrinsic scale, it is possible to convert other divergences into logarithmic form, using partial fraction identities; this includes the case of quadratic divergences, as has been applied to the linear sigma model. However the procedure must be carried out with due care, paying great attention to correct numerator factors.

In this work, we address the phenomenological consequences of explicit CP violation on direct Higgs–boson searches at high energy colliders. Having a restricted parameter space, we concentrate on the recently proposed gluino–axion model, and investigate the CP violation capability of the model subject to the recent experimental data. It is shown that the Higgs masses as well as their CP compositions are quite sensitive to the supersymmetric CP phases. The lightest Higgs is found to be nearly CP even to a good approximation whilst the remaining two heavy scalars do not have definite CP parities.

The electron mass operator in a strong magnetic field is calculated by summation of the leading log contributions in all orders of the perturbation theory. An influence of the strong field on the virtual photon polarization operator is taken into account. The contribution of higher Landau levels of virtual electrons, along with the ground Landau level, is shown to be essential in the leading log approximation.

In this paper we study the noncommutative description of the DBI Lagrangian and its T-dual counterpart. We restrict the freedoms of the noncommutativity parameters of these Lagrangians. Therefore the noncommutativity parameter, the effective metric, the effective coupling constant of the string and the extra modulus of the effective T-dual theory, can be expressed in terms of the closed string variables g, B, g_s and the noncommutativity parameter of the effective theory of open string.

The non-factorizable terms in the operator product expansion have been recognized as one of the theoretical obstacles for precision determination of the mixing parameter V_ub from semileptonic B decays. It is pointed out here that the recent CLEO data on the parameters of the heavy quark expansion λ₁ and , combined with a theoretical bound on λ₁ strongly favor the existence of a sizeable contribution of non-factorizable terms in semileptonic decays of D mesons. Thus these terms are likely to solve the long-standing problem of the deficit of semileptonic decay rate of the D mesons, and with better data their magnitude can be determined and used in studies of the parameter V_ub.