134 research outputs found
The proton spin sum rule chiral bag prediction, an update
We reevaluate a quark model prediction using the new QCD evolution function
calculated to the 3 loop order and conclude that this model compares favorably
with the new experimental results.Comment: 10 pages, 2 figures available by request, give fax numbe
Lightest-neutralino decays in R_p-violating models with dominant lambda^{prime} and lambda couplings
Decays of the lightest neutralino are studied in R_p-violating models with
operators lambda^{prime} L Q D^c and lambda L L E^c involving third-generation
matter fields and with dominant lambda^{prime} and lambda couplings.
Generalizations to decays of the lightest neutralino induced by subdominant
lambda^{prime} and lambda couplings are straightforward. Decays with the
top-quark among the particles produced are considered, in addition to those
with an almost massless final state. Phenomenological analyses for examples of
both classes of decays are presented. No specific assumption on the composition
of the lightest neutralino is made, and the formulae listed here can be easily
generalized to study decays of heavier neutralinos. It has been recently
pointed out that, for a sizable coupling lambda^{prime}_{333}, tau-sleptons may
be copiously produced at the LHC as single supersymmetric particles, in
association with top- and bottom-quark pairs. This analysis of neutralino
decays is, therefore, a first step towards the reconstruction of the complete
final state produced in this case.Comment: 40 pages, 11 figures, version to appear in JHE
Gauge Unification in Supersymmetric Intersecting Brane Worlds
We show that contrary to first expectations realistic three generation
supersymmetric intersecting brane world models give rise to phenomenologically
interesting predictions about gauge coupling unification. Assuming the most
economical way of realizing the matter content of the MSSM via intersecting
branes we obtain a model independent relation among the three gauge coupling
constants at the string scale. In order to correctly reproduce the
experimentally known values of sin^2[theta_W(M_z)] and alpha_s(M_z) this
relation leads to natural gauge coupling unification at a string scale close to
the standard GUT scale 2 x 10^16 GeV. Additional vector-like matter can push
the unification scale up to the Planck scale.Comment: 18 pages, harvmac & 3 figures; v2: one ref. adde
The ZZ' kinetic mixing in the light of the recent direct and indirect dark matter searches
Several constructions, of stringy origins or not, generate abelian gauge
extensions of the Standard Model (SM). Even if the particles of the SM are not
charged under this extra , one cannot avoid the presence of a kinetic
mixing between and the hypercharge . In this work, we
constraint drastically this kinetic mixing, taking into account the recent
experimental data from accelerator physics, direct detection and indirect
detection of dark matter. We show that the region respecting WMAP and
experimental constraints is now very narrowed along the pole line where
, being the gauge boson associated to the extra
.Comment: 9 pages, 3 figures, final version to appear in JCA
Spontaneous CP Violation in Non-Minimal Supersymmetric Models
We study the possibilities of spontaneous CP violation in the Next-to-Minimal
Supersymmetric Standard Model with an extra singlet tadpole term in the scalar
potential. We calculate the Higgs boson masses and couplings with radiative
corrections including dominant two loop terms. We show that it is possible to
satisfy the LEP constraints on the Higgs boson spectrum with non-trivial
spontaneous CP violating phases. We also show that these phases could account
for the observed value of epsilonK.Comment: 21 pages, 7 Figures in Encapsulated Postscrip
Global Study of the Simplest Scalar Phantom Dark Matter Model
We present a global study of the simplest scalar phantom dark matter model.
The best fit parameters of the model are determined by simultaneously imposing
(i) relic density constraint from WMAP, (ii) 225 live days data from direct
experiment XENON100, (iii) upper limit of gamma-ray flux from Fermi-LAT
indirect detection based on dwarf spheroidal satellite galaxies, and (iv) the
Higgs boson candidate with a mass about 125 GeV and its invisible branching
ratio no larger than 40% if the decay of the Higgs boson into a pair of dark
matter is kinematically allowed. The allowed parameter space is then used to
predict annihilation cross sections for gamma-ray lines, event rates for three
processes mono-b jet, single charged lepton and two charged leptons plus
missing energies at the Large Hadron Collider, as well as to evaluate the muon
anomalous magnetic dipole moment for the model.Comment: Matches JCAP accepted version. 25 pages, 7 figure
CP-Violating Effects in Neutralino Scattering and Annihilation
CP-violating effects that mix the CP-even and CP-odd Higgs bosons can have important consequences for annihilation and scattering of supersymmetric neutralino dark matter. Specifically, we study the dependence on the phase of the third generation trilinear couplings At and Ab. We find enhancements in the neutralino annihilation scattering rate which are typically factors of one to four; in the narrow regime of parameter space with neutralino mass close to half the Higgs mass, we find new (CP violating) resonances which may increase the annihilation cross section by factors up to 106. CP-violating effects can also modify the neutralino scattering rate off nucleons. For cross sections accessible to upcoming experiments, the rate can be enhanced by a factor as large as 2 or suppressed by a factor of up to 3; for lower cross sections, the suppression can be as large as seven orders of magnitude. We find cases in the region being probed by dark matter searches which are experimentally or cosmologically excluded when CP is conserved but are allowed when CP is violated. These effects are important for direct and indirect detection of neutralino dark matter in cryogenic detectors, the Earth, the Sun, the galactic halo and the galactic center.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49125/2/jhep072002052.pd
Hyperon production in Ar+KCl collisions at 1.76A GeV
We present transverse momentum spectra, rapidity distribution and
multiplicity of Lambda-hyperons measured with the HADES spectrometer in the
reaction Ar(1.76A GeV)+KCl. The yield of Xi- is calculated from our previously
reported Xi-/(Lambda+Sigma0) ratio and compared to other strange particle
multiplicities. Employing a strangeness balance equation the multiplicities of
the yet unmeasured charged Sigma hyperons can be estimated. Finally a
statistical hadronization model is used to fit the yields of pi-, K+, K0s, K-,
phi, Lambda and Xi-. The resulting chemical freeze-out temperature of T=(76+-2)
MeV is compared to the measured slope parameters obtained from fits to the
transverse mass distributions of the particles
Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation
The current status of electric dipole moments of diamagnetic atoms which
involves the synergy between atomic experiments and three different theoretical
areas -- particle, nuclear and atomic is reviewed. Various models of particle
physics that predict CP violation, which is necessary for the existence of such
electric dipole moments, are presented. These include the standard model of
particle physics and various extensions of it. Effective hadron level combined
charge conjugation (C) and parity (P) symmetry violating interactions are
derived taking into consideration different ways in which a nucleon interacts
with other nucleons as well as with electrons. Nuclear structure calculations
of the CP-odd nuclear Schiff moment are discussed using the shell model and
other theoretical approaches. Results of the calculations of atomic electric
dipole moments due to the interaction of the nuclear Schiff moment with the
electrons and the P and time-reversal (T) symmetry violating
tensor-pseudotensor electron-nucleus are elucidated using different
relativistic many-body theories. The principles of the measurement of the
electric dipole moments of diamagnetic atoms are outlined. Upper limits for the
nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained
combining the results of atomic experiments and relativistic many-body
theories. The coefficients for the different sources of CP violation have been
estimated at the elementary particle level for all the diamagnetic atoms of
current experimental interest and their implications for physics beyond the
standard model is discussed. Possible improvements of the current results of
the measurements as well as quantum chromodynamics, nuclear and atomic
calculations are suggested.Comment: 46 pages, 19 tables and 16 figures. A review article accepted for
EPJ
The Standard Cosmological Model
The Standard Model of Particle Physics (SMPP) is an enormously successful
description of high energy physics, driving ever more precise measurements to
find "physics beyond the standard model", as well as providing motivation for
developing more fundamental ideas that might explain the values of its
parameters. Simultaneously, a description of the entire 3-dimensional structure
of the present-day Universe is being built up painstakingly. Most of the
structure is stochastic in nature, being merely the result of the particular
realisation of the "initial conditions" within our observable Universe patch.
However, governing this structure is the Standard Model of Cosmology (SMC),
which appears to require only about a dozen parameters. Cosmologists are now
determining the values of these quantities with increasing precision in order
to search for "physics beyond the standard model", as well as trying to develop
an understanding of the more fundamental ideas which might explain the values
of its parameters. Although it is natural to see analogies between the two
Standard Models, some intrinsic differences also exist, which are discussed
here. Nevertheless, a truly fundamental theory will have to explain both the
SMPP and SMC, and this must include an appreciation of which elements are
deterministic and which are accidental. Considering different levels of
stochasticity within cosmology may make it easier to accept that physical
parameters in general might have a non-deterministic aspect.Comment: 16 pages, 2 figures, invited talk at "Theory Canada 1", June 2005,
Vancouve
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