O(alpha_s alpha_t) (non)decoupling effects within the top-sector of the MSSM

In this paper we compute the $\mathcal{O}(\alpha_s \alpha_t)$ threshold corrections to the running strong coupling constant, the top-Yukawa coupling and the top-quark mass within the MSSM. These parameters present a non-decoupling behaviour with the supersymmetry scale $M_{\rm SUSY}$. Our numerical analysis shows that the mixed QCD-Yukawa corrections can amount to few GeV for the running top-quark mass and range at the percent level for the top-Yukawa coupling.Comment: References added; new lines in the plots displayed; more details about the calculation include

Two-loop matching coefficients for the strong coupling in the MSSM

When relating the strong coupling $\alpha_s$, measured at the scale of the $Z$ boson mass, to its numerical value at some higher energy, for example the scale of Grand Unification, it is important to include higher order corrections both in the running of $\alpha_s$ and the decoupling of the heavy particles. We compute the two-loop matching coefficients for $\alpha_s$ within the Minimal Supersymmetric Standard Model (MSSM) which are necessary for a consistent three-loop evolution of the strong coupling constant. Different scenarios for the hierarchy of the supersymmetric scales are considered and the numerical effects are discussed. We find that the three-loop effects can be as large as and sometimes even larger than the uncertainty induced by the current experimental accuracy of $\alpha_s(M_Z)$.Comment: 22 pages, 8 figures (13 ps/eps-files

Ghost contributions to charmonium production in polarized high-energy collisions

In a previous paper [Phys. Rev. D 68, 034017 (2003)], we investigated the inclusive production of prompt J/psi mesons in polarized hadron-hadron, photon-hadron, and photon-photon collisions in the factorization formalism of nonrelativistic quantum chromodynamics providing compact analytic results for the double longitudinal-spin asymmetry A_{LL}. For convenience, we adopted a simplified expression for the tensor product of the gluon polarization four-vector with its charge conjugate, at the expense of allowing for ghost and anti-ghosts to appear as external particles. While such ghost contributions cancel in the cross section asymmetry A_{LL} and thus were not listed in our previous paper, they do contribute to the absolute cross sections. For completeness and the reader's convenience, they are provided in this addendum.Comment: 5 page

O(\alpha_s^2) corrections to the running top-Yukawa coupling and the mass of the lightest Higgs boson in the MSSM

In this paper we propose a method to compute the running top-Yukawa coupling in supersymmetric models with heavy mass spectrum based on the "running" and "decoupling" procedure. In order to enable this approach we compute the two-loop SUSY-QCD radiative corrections required in the decoupling process. The method has the advantage that large logarithmic corrections are automatically resummed through the Renormalization Group Equations. As phenomenological application we study the effects of this approach on the prediction of the lightest Higgs boson mass at three-loop accuracy. We observe a significant reduction of the renormalization scale dependence as compared to the direct method, that is based on the conversion relation between the running and pole mass for the top quark. The effect of resummation of large logarithmic contributions consists in an increased prediction for the Higgs boson mass, an observation in agreement with the previous analyses.Comment: 24 pages, 9 figures; one more figure added; reference list extende

Acoustic attenuation rate in the Fermi-Bose model with a finite-range fermion-fermion interaction

We study the acoustic attenuation rate in the Fermi-Bose model describing a mixtures of bosonic and fermionic atom gases. We demonstrate the dramatic change of the acoustic attenuation rate as the fermionic component is evolved through the BEC-BCS crossover, in the context of a mean-field model applied to a finite-range fermion-fermion interaction at zero temperature, such as discussed previously by M.M. Parish et al. [Phys. Rev. B 71, 064513 (2005)] and B. Mihaila et al. [Phys. Rev. Lett. 95, 090402 (2005)]. The shape of the acoustic attenuation rate as a function of the boson energy represents a signature for superfluidity in the fermionic component