278 research outputs found
O(alpha_s alpha_t) (non)decoupling effects within the top-sector of the MSSM
In this paper we compute the 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 . 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 , measured at the scale of the
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 and the decoupling of the heavy particles. We
compute the two-loop matching coefficients for 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 .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
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