1,781 research outputs found
High energy neutrinos from neutralino annihilations in the Sun
Neutralino annihilations in the Sun to weak boson and top quark pairs lead to
high-energy neutrinos that can be detected by the IceCube and KM3 experiments
in the search for neutralino dark matter. We calculate the neutrino signals
from real and virtual WW, ZZ, Zh, and production and decays,
accounting for the spin-dependences of the matrix elements, which can have
important influences on the neutrino energy spectra. We take into account
neutrino propagation including neutrino oscillations, matter-resonance,
absorption, and nu_tau regeneration effects in the Sun and evaluate the
neutrino flux at the Earth. We concentrate on the compelling Focus Point (FP)
region of the supergravity model that reproduces the observed dark matter relic
density. For the FP region, the lightest neutralino has a large bino-higgsino
mixture that leads to a high neutrino flux and the spin-dependent neutralino
capture rate in the Sun is enhanced by 10^3 over the spin-independent rate. For
the standard estimate of neutralino captures, the muon signal rates in IceCube
are identifiable over the atmospheric neutrino background for neutralino masses
above M_Z up to 400 GeV.Comment: 45 pages, 18 figures and 5 tables, PRD versio
Relativistic and Binding Energy Corrections to Direct Photon Production In Upsilon Decay
A systematic gauge-invariant method is used to calculate the rate for an
upsilon meson to decay inclusively into a prompt photon. An expansion is made
in the quark relative velocity v, which is a small natural parameter for heavy
quark systems. Inclusion of these O(v^2) corrections tends to increase the
photon rate in the middle z range and to lower it for larger z, a feature
supported by the data.Comment: 13 pages, LateX, One figure (to be published in Phys. Rev. D, Sept.
1, 1996
Colour-Octet Effects in Radiative Decays
We investigate the effects of colour-octet contributions to the radiative
decay within the Bodwin, Braaten and Lepage NRQCD factorization
framework. Photons coming both from the coupling to hard processes (`direct')
and by collinear emission from light quarks (`fragmentation') are consistently
included at next-to-leading order (NLO) in . An estimate for the
non-perturbative matrix elements which enter in the final result is then
obtained. By comparing the NRQCD prediction at NLO for total decay rates with
the experimental data, it is found that the non-perturbative parameters must be
smaller than expected from the na\"\i ve scaling rules of NRQCD. Nevertheless,
colour-octet contributions to the shape of the photon spectrum turn out to be
significant.Comment: 25 pages, Latex, 8 figure
Photoproduction of h_c
Using the NRQCD factorization formalism, we calculate the total cross section
for the photoproduction of h_c mesons. We include color-octet and color-singlet
mechanisms as well as next-to-leading order perturbative QCD corrections. The
theoretical prediction depends on two nonperturbative matrix elements that are
not well determined from existing data on charmonium production. For reasonable
values of these matrix elements, the cross section is large enough that the h_c
may be observable at the E831 experiment and at the HERA experiments.Comment: Revtex file 8 pages, 1 figure. Macros needed: epsf,floats,rotate
Minor typos changed, and reference added. Version to be published in
Phys.Rev.
Color-Octet Fraction in J/Psi Production and Absorption
The cross section between a pair and a nucleon is small and
sensitive to the separation if the pair is in a color-singlet
state, but very large and insensitive to the separation if it is in a
color-octet state. We use this property in an absorption model involving both
color components to deduce the color structure of pairs produced in
reactions. Our analysis shows that the NA3, NA38 and E772
data are not inconsistent with the theoretical picture that color-octet and
color-singlet precursors are produced in roughly equal proportions if the
produced color-singlet precursors are pointlike and transparent. However, if
the color-singlet precursors are not transparent but have a cross section of a
few mb, these data do show a definite preference for a larger fraction of
color-singlet precursors. In either case, the color-octet fraction increases
with , approaching unity as becomes large.Comment: 9 pages, updated to include new result
Ordered spectral statistics in 1D disordered supersymmetric quantum mechanics and Sinai diffusion with dilute absorbers
Some results on the ordered statistics of eigenvalues for one-dimensional
random Schr\"odinger Hamiltonians are reviewed. In the case of supersymmetric
quantum mechanics with disorder, the existence of low energy delocalized states
induces eigenvalue correlations and makes the ordered statistics problem
nontrivial. The resulting distributions are used to analyze the problem of
classical diffusion in a random force field (Sinai problem) in the presence of
weakly concentrated absorbers. It is shown that the slowly decaying averaged
return probability of the Sinai problem, \mean{P(x,t|x,0)}\sim \ln^{-2}t, is
converted into a power law decay, \mean{P(x,t|x,0)}\sim t^{-\sqrt{2\rho/g}},
where is the strength of the random force field and the density of
absorbers.Comment: 10 pages ; LaTeX ; 4 pdf figures ; Proceedings of the meeting
"Fundations and Applications of non-equilibrium statistical mechanics",
Nordita, Stockholm, october 2011 ; v2: appendix added ; v3: figure 2.left
adde
Solutions to the R_b, R_c and alpha_s puzzles by Vector Fermions
We propose two minimal extensions of Standard Model, both of which can easily
accommodate the recent puzzling observations about the excess in , the
deficit in and the discrepancy in the low energy and high energy
determinations of . Each model requires three additional heavy
vectorial fermions in order to resolve the puzzles. The current
phenomenological constraints and the new potential phenomena are also
discussed.Comment: 12 pages, in LaTeX, postscript file also appear
http://www.uic.edu/~keung/pub/rbrc.p
Spin Dependence of Dark Matter Scattering
New experiments designed to discover a weakly interacting dark matter (DM)
particle via spin dependent scattering can distinguish models of electroweak
symmetry breaking. The plane of spin dependent versus spin independent DM
scattering cross sections is a powerful model diagnostic. We detail
representative predictions of mSUGRA, singlet extended SM and MSSM, a new Dirac
neutrino, Littlest Higgs with T-parity (LHT) and Minimal Universal Extra
Dimensions (mUED) models. Of these models, the nMSSM has the largest spin
dependent (SD) cross section. It has a very light neutralino which would give
lower energy nuclear recoils. The Focus Point region of mSUGRA, mUED and the
right handed neutrino also predict a very large SD cross section and predict a
large signal of high energy neutrinos in the IceCube experiment from
annihilations of dark matter in the Sun. We also describe a model independent
treatment of the scattering of DM particles of different intrinsic spins.Comment: 40 pages, 13 figures, 1 tabl
How large could the R-parity violating couplings be?
We investigate in detail the predictions coming from the d=4 operators for
proton decay. We find the most general constraints for the R-parity violating
couplings coming from proton decay, taking into account all fermion mixing and
in different supersymmetric scenarios.Comment: 8 pages, several corrections, to appear in J.Phys.G (2005
The Soft Gluon Emission Process in the Color-Octet Model for Heavy Quarkonium Production
The Color-Octet Model has been used successfully to analyze many problems in
heavy quarkonium production. We examine some of the conceptual and practical
problems of the soft gluon emission process in the Color-Octet Model. We use a
potential model to describe the initial and final states in the soft gluon
emission process, as the emission occurs at a late stage after the production
of the heavy quark pair. It is found in this model that the soft gluon M1
transition, 1S0(8)->3S1(1), dominates over the E1 transition, 3PJ(8)->3S1(1),
for J/psi and psi' production. Such a dominance may help resolve the questions
of isotropic polarization and color-octet matrix element universality in the
Color-Octet Model.Comment: 26 pages, in LaTe
- …