1,507 research outputs found
Baryon Masses in Partially Quenched Heavy Hadron Chiral Perturbation Theory
The masses of baryons containing a heavy quark are calculated to
next-to-leading order in partially quenched heavy hadron chiral perturbation
theory. Calculations are performed for three light flavors in the isospin limit
and additionally for two light non-degenerate flavors. The results presented
are necessary for extrapolating lattice QCD and partially quenched lattice QCD
calculations of the heavy hadron masses.Comment: 20 pages, 2 figures, RevTex
Electroweak Corrections using Effective Field Theory: Applications to the LHC
Electroweak Sudakov logarithms at high energy, of the form alpha/sin^2
theta_W^n log^m s/M_{Z,W}^2, are summed using effective theory (EFT) methods.
The exponentiation of Sudakov logarithms and factorization is discussed in the
EFT formalism. Radiative corrections are computed to scattering processes in
the standard model involving an arbitrary number of external particles. The
computations include non-zero particle masses such as the t-quark mass,
electroweak mixing effects which lead to unequal W and Z masses and a massless
photon, and Higgs corrections proportional to the top quark Yukawa coupling.
The structure of the radiative corrections, and which terms are summed by the
EFT renormalization group is discussed in detail. The omitted terms are smaller
than 1%. We give numerical results for the corrections to dijet production,
dilepton production, t-\bar t production, and squark pair production. The
purely electroweak corrections are significant -- about 15% at 1 TeV,
increasing to 30% at 5 TeV, and they change both the scattering rate and
angular distribution. The QCD corrections (which are well-known) are also
computed with the EFT. They are much larger -- about a factor of four at 1 TeV,
increasing to a factor of thirty at 5 TeV. Mass effects are also significant;
the q \bar q -> t \bar t rate is enchanced relative to the light-quark
production rate by 40%.Comment: Additional details added on exponentiation, and the form of the
Sudakov series. Figures darkened to print better. 40 pages, 40 figure
The double charm decays of Meson in the Perturbative QCD Approach
We make a systematic investigation on the double charm decays of meson,
by employing the perturbative QCD approach based on factorization. It is
found that the non-factorizable emission diagrams are not negligible in these
channels. We predict the branching ratios of these decays and also the
transverse polarization fractions of decays, % where V denote the vector meson.
We find that the magnitudes of the branching ratios of the decays
and are very close to
each other, which are well suited to extract the Cabibbo-Kobayashi-Maskawa
angle through the amplitude relations. In addition, a large transverse
polarization contribution that can reach is predicted in some of
the meson decay to two vector charmed mesons.Comment: 22 pages, 5 tables, to appear at PRD. arXiv admin note: text overlap
with arXiv:1112.125
Multiple electron trapping in the fragmentation of strongly driven molecules
We present a theoretical quasiclassical study of the formation, during
Coulomb explosion, of two highly excited neutral H atoms (double H) of
strongly driven H. In this process, after the laser field is turned off
each electron occupies a Rydberg state of an H atom. We show that two-electron
effects are important in order to correctly account for double H
formation. We find that the route to forming two H atoms is similar to
pathway B that was identified in Phys. Rev. A {\bf 85} 011402 (R) as one of the
two routes leading to single H formation. However, instead of one
ionization step being "frustrated" as is the case for pathway B, both
ionization steps are "frustrated" in double H formation. Moreover, we
compute the screened nuclear charge that drives the explosion of the nuclei
during double H formation.Comment: 4 pages, 6 figure
Drag and diffusion coefficients of mesons in hot hadronic matter
The drag and diffusion coefficients of a hot hadronic medium consisting of
pions, kaons and eta using open beauty mesons as a probe have been evaluated.
The interaction of the probe with the hadronic matter has been treated in the
framework of chiral perturbation theory. It is observed that the magnitude of
both the transport coefficients are significant, indicating substantial amount
of interaction of the heavy mesons with the thermal bath. The results may have
significant impact on the experimental observables like the suppression of
single electron spectra originating from the decays of heavy mesons produced in
nuclear collisions at RHIC and LHC energiesComment: 5 pages and 3 fig
Ultrasoft Renormalization in Non-Relativistic QCD
For Non-Relativistic QCD the velocity renormalization group correlates the
renormalization scales for ultrasoft, potential and soft degrees of freedom.
Here we discuss the renormalization of operators by ultrasoft gluons. We show
that renormalization of soft vertices can induce new operators, and also
present a procedure for correctly subtracting divergences in mixed
potential-ultrasoft graphs. Our results affect the running of the
spin-independent potentials in QCD. The change for the NNLL t-tbar cross
section near threshold is very small, being at the 1% level and essentially
independent of the energy. We also discuss implications for analyzing
situations where mv^2 ~ Lambda_QCD.Comment: 31 pages, 11 fig
Locality of quark-hadron duality and deviations from quark counting rules above resonance region
We show how deviations from the dimensional scaling laws for exclusive
processes may be related to a breakdown in the locality of quark-hadron
duality. The essential principles are illustrated in a pedagogic model of a
composite system with two spinless charged constituents, for which a dual
picture for the low-energy resonance phenomena and high-energy scaling behavior
can be established. We introduce the concept of "restricted locality" of
quark-hadron duality and show how this results in deviations from the pQCD
quark counting rules above the resonance region. In particular it can be a
possible source for oscillations about the smooth quark counting rule, as seen
e.g. in the 90-degree differential cross sections for .Comment: The way to present Eqs. (2), (4), (7) are changed while physics
contents and calculations are left intact; Additional explanations for the
forward and large-angle duality are added; Three more references are
included; Version to appear on Phys. Rev. Let
Deriving the existence of bound states from the X(3872) and Heavy Quark Symmetry
We discuss the possibility and the description of bound states between
and mesons. We argue that the existence of such a bound state can
be deduced from (i) the weakly bound X(3872) state, (ii) certain assumptions
about the short range dynamics of the system and (iii) heavy quark
symmetry. From these assumptions the binding energy of the possible
bound states is determined, first in a theory containing only
contact interactions which serves as a straightforward illustration of the
method, and then the effects of including the one pion exchange potential are
discussed. In this latter case three isoscalar states are predicted: a positive
and negative C-parity state with a binding energy of and below threshold respectively, and a positive C-parity
shallow state located almost at the threshold. However,
large uncertainties are generated as a consequence of the corrections
from heavy quark symmetry. Finally, the newly discovered isovector
state can be easily accommodated within the present framework by a minor
modification of the short range dynamics.Comment: 21 pages, 3 figures; a sign error in the potential has been corrected
and new predictions have been compute
Deciphering top flavor violation at the LHC with B factories
The LHC will have unprecedented sensitivity to flavor-changing neutral
current (FCNC) top quark decays, whose observation would be a clear sign of
physics beyond the standard model. Although many details of top flavor
violation are model dependent, the standard model gauge symmetries relate top
FCNCs to other processes, which are strongly constrained by existing data. We
study these constraints in a model independent way, using a low energy
effective theory from which the new physics is integrated out. We consider the
most important operators which contribute to top FCNCs and analyze the current
constraints on them. We find that the data rule out top FCNCs at a level
observable at the LHC due to most of the operators comprising left-handed first
or second generation quark fields, while there remains a substantial window for
top decays mediated by operators with right-handed charm or up quarks. If FCNC
top decays are observed at the LHC, such an analysis may help decipher the
underlying physics.Comment: 17 pages, 5 figures; some typos correcte
On the structure of large N cancellations in baryon chiral perturbation theory
We show how to compute loop graphs in heavy baryon chiral perturbation theory
including the full functional dependence on the ratio of the Delta--nucleon
mass difference to the pion mass, while at the same time automatically
incorporating the 1/N cancellations that follow from the large-N spin-flavor
symmetry of baryons in QCD. The one-loop renormalization of the baryon axial
vector current is studied to demonstrate the procedure. A new cancellation is
identified in the one-loop contribution to the baryon axial vector current. We
show that loop corrections to the axial vector currents are exceptionally
sensitive to deviations of the ratios of baryon-pion axial couplings from SU(6)
values
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