18,051 research outputs found
Flavor-Singlet B-Decay Amplitudes in QCD Factorization
Exclusive hadronic B-meson decays into two-body final states consisting of a
light pseudoscalar or vector meson along with an eta or eta' meson are of great
phenomenological interest. Their theoretical analysis involves decay mechanisms
that are unique to flavor-singlet states, such as their coupling to gluons or
their ``intrinsic charm'' content. These issues are studied systematically in
the context of QCD factorization and the heavy-quark expansion. Theory can
account for the experimental data on the B->K^{(*)} eta^{(')} branching
fractions, albeit within large uncertainties.Comment: 25 pages, 5 figure
DLCQ and Plane Wave Matrix Big Bang Models
We study the generalisations of the Craps-Sethi-Verlinde matrix big bang
model to curved, in particular plane wave, space-times, beginning with a
careful discussion of the DLCQ procedure. Singular homogeneous plane waves are
ideal toy-models of realistic space-time singularities since they have been
shown to arise universally as their Penrose limits, and we emphasise the role
played by the symmetries of these plane waves in implementing the flat space
Seiberg-Sen DLCQ prescription for these curved backgrounds. We then analyse
various aspects of the resulting matrix string Yang-Mills theories, such as the
relation between strong coupling space-time singularities and world-sheet
tachyonic mass terms. In order to have concrete examples at hand, in an
appendix we determine and analyse the IIA singular homogeneous plane wave -
null dilaton backgrounds.Comment: 29 pages, v2: reference added + minor cosmetic correction
Curvature bounds for configuration spaces
We show that the configuration space over a manifold M inherits many
curvature properties of the manifold. For instance, we show that a lower Ricci
curvature bound on M implies for the configuration space a lower Ricci
curvature bound in the sense of Lott-Sturm-Villani, the Bochner inequality,
gradient estimates and Wasserstein contraction. Moreover, we show that the heat
flow on the configuration space, or the infinite independent particle process,
can be identified as the gradient flow of the entropy.Comment: 34 page
alpha_s and the tau hadronic width: fixed-order, contour-improved and higher-order perturbation theory
The determination of from hadronic decays is revisited,
with a special emphasis on the question of higher-order perturbative
corrections and different possibilities of resumming the perturbative series
with the renormalisation group: fixed-order (FOPT) vs. contour-improved
perturbation theory (CIPT). The difference between these approaches has evolved
into a systematic effect that does not go away as higher orders in the
perturbative expansion are added. We attempt to clarify under which
circumstances one or the other approach provides a better approximation to the
true result. To this end, we propose to describe the Adler function series by a
model that includes the exactly known coefficients and theoretical constraints
on the large-order behaviour originating from the operator product expansion
and the renormalisation group. Within this framework we find that while CIPT is
unable to account for the fully resummed series, FOPT smoothly approaches the
Borel sum, before the expected divergent behaviour sets in at even higher
orders. Employing FOPT up to the fifth order to determine in the
\MSb scheme, we obtain ,
corresponding to . Improving
this result by including yet higher orders from our model yields
, which after evolution leads to
. Our results are lower than previous values
obtained from decays.Comment: 42 pages, 9 figures; appendix on Adler function in the complex plane
added. Version to appear in JHE
QCD factorization for B->PP and B->PV decays
A comprehensive study of exclusive hadronic B-meson decays into final states
containing two pseudoscalar mesons (PP) or a pseudoscalar and a vector meson
(PV) is presented. The decay amplitudes are calculated at leading power in
Lambda_{QCD}/m_b and at next-to-leading order in alpha_s using the QCD
factorization approach. The calculation of the relevant hard-scattering kernels
is completed. Important classes of power corrections, including
``chirally-enhanced'' terms and weak annihilation contributions, are estimated
and included in the phenomenological analysis. Predictions are presented for
the branching ratios of the complete set of the 96 decays of B^-, B^0, and B_s
mesons into PP and PV final states, and for most of the corresponding CP
asymmetries. Several decays and observables of particular phenomenological
interest are discussed in detail, including the magnitudes of the penguin
amplitudes in PP and PV final states, an analysis of the pi-rho system, and the
time-dependent CP asymmetry in the K phi and K eta' final states.Comment: 92 pages, 13 figures, 28 tables; typos and errors in data tables
corrected; version to appear in Nuclear Physics
Investigating sexual strategies in a social community website
In this exploratory study we tried to corroborate existing findings of Sexual Strategies Theory (SST, Buss & Schmitt, 1993) by using data collected from an online community.
A random sample of N = 460 German user profiles was drawn from Myspace, a social networking website. Sexual interests reported by the users were analyzed separately for men and women: âDatingâ served as an indicator of short-term and interest in âSerious Relationshipâ as an indicator of long-term sexual strategy. Consistent with SST, a higher
percentage of male than female users was interested in dating. However, men were also more interested in serious relationships, indicating that online partner search itself might be a short-term sexual strategy
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