10,582 research outputs found
Electroweak Sudakov Corrections and the Top Quark Forward-Backward Asymmetry
The Standard Model (SM) prediction of the top quark forward backward
asymmetry is shown to be slightly enhanced by a correction factor of 1.05 due
to electroweak Sudakov (EWS) logarithms of the form (\alpha/sin^2 \theta_W)^n
log^{m< 2n} (s/M_{W,Z}^2). The EWS effect on the dijet and t \bar{t} invariant
mass spectra is significant, reducing the SM prediction by ~20, 10 %
respectively for the highest invariant masses measured at the LHC, and changing
the shape of the high-mass tail of the spectrum. These corrections
significantly affect measurements of the top quark invariant mass spectrum and
the search for an excess of events related to the top quark forward-backward
asymmetry.Comment: 5 pages, 2 figure
Radiative Corrections to Longitudinal and Transverse Gauge Boson and Higgs Production
Radiative corrections to gauge boson and Higgs production computed recently
using soft-collinear effective theory (SCET) require the one-loop high-scale
matching coefficients in the standard model. We give explicit expressions for
the matching coefficients for the effective field theory (EFT) operators for q
qbar -> VV and q qbar -> phi^+ phi for a general gauge theory with an arbitrary
number of gauge groups. The group theory factors are given explicitly for the
standard model, including both QCD and electroweak corrections.Comment: 16 pages, 49 figure
Solutions of the Ginsparg-Wilson Relation
We analyze general solutions of the Ginsparg-Wilson relation for lattice
Dirac operators and formulate a necessary condition for such operators to have
non-zero index in the topologically nontrivial background gauge fields.Comment: 6 pages, latex, no figures, set T to 1 in eqs. (10)--(13
Study of Bc->KK decay with perturbative QCD approach
In the framework of the perturbative QCD approach, we study the charmless
pure weak annihilation Bc->KK decay and find that the branching ratio
BR(Bc->KK) O(10^-7). This prediction is so tiny that the Bc->KK decay might be
unmeasurable at the Large Hadron Collider.Comment: Revtex4, 12 pages, 1 figure
The peculiar molecular envelope around the post-AGB star IRAS 08544--4431
Circumbinary disks have been hypothesized to exist around a number of binary
post-AGB stars. Although most of the circumbinary disks have been inferred
through the near IR excess, a few of them are strong emitters of molecular
emission. Here we present high angular resolution observations of the emission
of CO and its isotopomer CO J=2--1 line from the circumstellar
envelope around the binary post-AGB star IRAS 085444431, which is one of the
most prominent members of this class of objects. We find that the envelope is
resolved in our observations and two separate components can be identified: (a)
a central extended and strong component with very narrow linewidth between 2 -
6 \kms; (b) a weak bipolar outflow with expansion velocity up to 8 \kms. The
central compact component possesses low and variable CO/CO J=2--1
line ratio, indicating optically thick emission of the main isotope. We
estimate a molecular gas mass of 0.0047 M for this component based on
the optically thinner CO J=2--1 line. We discuss the relation of the
molecular envelope and the circumbinary disk inferred from near IR excess and
compare with other known cases where the distribution of molecular gas has been
imaged at high angular resolution.Comment: 14 pages, 4 figures. Accepted for publication in Astrophysical
Journa
Speed and Adaptability of Overlap Fermion Algorithms
We compare the efficiency of four different algorithms to compute the overlap
Dirac operator, both for the speed, i.e., time required to reach a desired
numerical accuracy, and for the adaptability, i.e., the scaling of speed with
the condition number of the (square of the) Wilson Dirac operator. Although
orthogonal polynomial expansions give good speeds at moderate condition number,
they are highly non-adaptable. One of the rational function expansions, the
Zolotarev approximation, is the fastest and is adaptable. The conjugate
gradient approximation is adaptable, self-tuning, and nearly as fast as the ZA.Comment: 30 Pages, 7 Figures, RevTex4, New results for Zolotarev Algorithm,
causing major changes in Section V and Concluding sectio
Influence of retardation effects on 2D magnetoplasmon spectrum
Within dissipationless limit the magnetic field dependence of magnetoplasmon
spectrum for unbounded 2DEG system found to intersect the cyclotron resonance
line, and, then approaches the frequency given by light dispersion relation.
Recent experiments done for macroscopic disc-shape 2DEG systems confirm theory
expectations.Comment: 2 pages,2 figure
What is Double Parton Scattering?
Processes such as double Drell-Yan and same-sign WW production have
contributions from double parton scattering, which are not well-defined because
of a delta(z_\perp=0) singularity that is generated by QCD evolution. We study
the single and double parton contributions to these processes, and show how to
handle the singularity using factorization and operator renormalization. We
compute the QCD evolution of double parton distribution functions (PDFs) due to
mixing with single PDFs. The modified evolution of dPDFs at z_\perp=0,
including generalized dPDFs for the non-forward case, is given in the appendix.
We include a brief discussion of the experimental interpretation of dPDFs and
how they can probe flavor, spin and color correlations of partons in hadrons.Comment: 7 pages, 12 figures; v2: appendix fixed and extended, journal versio
Electroweak Sudakov Corrections using Effective Field Theory
Electroweak Sudakov corrections of the form alpha^n log^m s/M_{W,Z}^2 are
summed using renormalization group evolution in soft-collinear effective theory
(SCET). Results are given for the scalar, vector and tensor form-factors for
fermion and scalar particles. The formalism for including massive gauge bosons
in SCET is developed.Comment: 5 page
- …