15,639 research outputs found
Kinematical Constraints on QCD Factorization in the Drell-Yan Process
We study factorization schemes for parton shower models in hadron-hadron
collisions. As an example, we calculate lepton pair production mediated by a
virtual photon in quark--anti-quark annihilation, and we compare factorized
cross sections obtained in the conventional scheme with those
obtained in a factorization scheme in which a kinematical constraint due to
parton radiation is taken into account. We discuss some properties of
factorized cross sections.Comment: 10 pages, PTPTeX.sty, 1 Postscript figur
Two-loop Renormalization Factors of Dimension-six Proton Decay Operators in the Supersymmetric Standard Models
The renormalization factors of the dimension-six effective operators for
proton decay are evaluated at two-loop level in the supersymmetric grand
unified theories. For this purpose, we use the previous results in which the
quantum corrections to the effective Kahler potential are evaluated at
two-loop level. Numerical values for the factors are presented in the case of
the minimal supersymmetric SU(5) grand unified model. We also derive a simple
formula for the one-loop renormalization factors for any higher-dimensional
operators in the Kahler potential, assuming that they are induced by the gauge
interactions.Comment: 11 pages. Version accepted for publication in Phys. Lett.
A characterization of the alpha-connections on the statistical manifold of multivariate normal distributions
We study a statistical manifold
of multivariate normal distributions, where is the Fisher metric and
is the Amari-Chentsov connection and is its
conjugate connection. We will show that it admits a solvable Lie group
structure and moreover the Amari-Chentsov connection on
will be characterized by the conjugate symmetry, i.e., a
curvatures identity of a connection and its conjugate
connection
Bulk scalar emission from a rotating black hole pierced by a tense brane
We study the emission of scalar fields into the bulk from a six-dimensional
rotating black hole pierced by a 3-brane. We determine the angular eigenvalues
in the presence of finite brane tension by using the continued fraction method.
The radial equation is integrated numerically, giving the absorption
probability (graybody factor) in a wider frequency range than in the
preexisting literature. We then compute the power and angular momentum emission
spectra for different values of the rotation parameter and brane tension, and
compare their relative behavior in detail. As is expected from the earlier
result for a nonrotating black hole, the finite brane tension suppresses the
emission rates. As the rotation parameter increases, the power spectra are
reduced at low frequencies due to the smaller Hawking temperature and are
enhanced at high frequencies due to superradiance. The angular momentum spectra
are enhanced over the whole frequency range as the rotation parameter
increases. The spectra and the amounts of energy and angular momentum radiated
away into the bulk are thus determined by the interplay of these effects.Comment: 10 pages, 7 figures; v2: references added; v3: Figs. 4, 5, 6
corrected. Numerical results changed; v4: references added, minor
clarification, accepted for publication in Physical Review
Spin-polarized scanning tunneling microscopy of half-metallic ferromagnets: Non-quasiparticle contributions
The role of the many-body (spin-polaronic) effects in the scanning tunneling
spectroscopy of half-metallic ferromagnets (HMF) is considered. It is shown
that the non-quasiparticle (NQP) states exist in the majority or minority spin
gap in the presence of arbitrary external potential and, in particular, at the
surfaces and interfaces. Energy dependence of the NQP density of states is
obtained in various models of HMF, an important role of the hybridization
nature of the energy gap being demonstrated. The corresponding temperature
dependence of spin polarization is calculated. It is shown that the NQP states
result in a sharp bias dependence of the tunneling conductance near zero bias.
Asymmetry of the NQP states with respect to the Fermi energy provides an
opportunity to separate phonon and magnon peaks in the inelastic spectroscopy
by STM.Comment: 13 pages, 6 figure
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