274 research outputs found
Effective CP violation in the Standard Model
We study the strength of effective CP violation originating from the CKM
matrix in the effective action obtained by integrating out the fermions in the
Standard Model. Using results obtained by Salcedo for the effective action in a
general chiral gauge model, we find that there are no CKM CP-violating terms to
fourth order in a gauge-covariant derivative expansion that is non-perturbative
in the Higgs field. The details of the calculation suggest that, at zero
temperature, the strength of CP violation is approximately independent of the
overall scale of the Yukawa couplings. Thus, order of magnitude estimates based
on Jarlskog's invariant could be too small by a factor of about 10^{17}.Comment: 19 pages, no figure
Electroproduction and Hadroproduction of Light Gluinos
In a class of supergravity models, the gluino and photino are massless at
tree level and receive small masses through radiative corrections. In such
models, one expects a gluino-gluon bound state, the , to have a mass of
between 1.0 and 2.2 GeV and a lifetime between and
seconds. Applying peturbative QCD methods (whose validity we discuss), we
calculate the production cross sections of 's in , , ,
and collisions. Signatures are also discussed.Comment: 10 pages, latex, 6 figures uuencoded, figures also available via
anonymous ftp to ftp://physics.wm.edu/pub/gluinofig.p
Affleck-Dine (Pseudo)-Dirac Neutrinogenesis
We consider the Affleck-Dine mechanism for leptogenesis in the minimal MSSM
with Dirac or Pseudo-Dirac neutrinos. The rolling of scalars along D-flat
directions generates a left-right asymmetry in the sneutrino sector, only the
left part of which is transferred to a baryon asymmetry via sphaleron
transitions. In the pure Dirac case the baryon asymmetry of the Universe is
thus mirrored by an equal and opposite asymmetry in the leptons. The mechanism
is also found to work when the neutrinos are pseudo-Dirac. No additional field
needs to be added to the MSSM other than the right-handed neutrino.Comment: Latex, 3 figures, 1 bib file, 2 added reference, 1 minor correction,
1 added commen
Axion-like particles as ultra high energy cosmic rays?
If Ultra High Energy Cosmic Rays (UHECRs) with E>4 10^{19} eV originate from
BL Lacertae at cosmological distances as suggested by recent studies, the
absence of the GZK cutoff can not be reconciled with Standard-Model particle
properties. Axions would escape the GZK cutoff, but even the coherent
conversion and back-conversion between photons and axions in large-scale
magnetic fields is not enough to produce the required flux. However, one may
construct models of other novel (pseudo)scalar neutral particles with
properties that would allow for sufficient rates of particle production in the
source and shower production in the atmosphere to explain the observations. As
an explicit example for such particles we consider SUSY models with light
sgoldstinos.Comment: 5 pages, 2 postscript figures, ref. adde
Cosmic microwave background and large scale structure limits on the interaction between dark matter and baryons
We study the effect on the cosmic microwave background (CMB) anisotropy and
large scale structure (LSS) power spectrum of a scattering interaction between
cold dark matter and baryons. This scattering alters the CMB anisotropy and LSS
spectrum through momentum transfer between the cold dark matter particles and
the baryons. We find that current CMB observations can put an upper limit on
the scattering cross section which is comparable with or slightly stronger than
previous disk heating constraints at masses greater than 1 GeV, and much
stronger at smaller masses. When large-scale structure constraints are added to
the CMB limits, our constraint is more stringent than this previous limit at
all masses. In particular, a dark matter-baryon scattering cross section
comparable to the ``Spergel-Steinhardt'' cross section is ruled out for dark
matter mass greater than 1 GeV.Comment: 8 pages, 2 figures, use RevTeX4, submitted to PRD replaced with
revised versio
One-Loop Helicity Amplitudes for Parton Level Virtual Compton Scattering
We calculate the one-loop QCD virtual corrections to all helicity amplitudes
for parton level virtual Compton scattering processes. We include the
amplitudes both on quark target process and on gluon
target process . The infrared pole structure of the
amplitudes is in agreement with the prediction of Catani's general formalism
for the singularities of one-loop amplitudes, while expressions for the finite
remainder are given in terms of logarithms and dilogarithms that are real in
the physical region.Comment: 16 pages, 2 figures, detailed comparison with DVCS include
Time variation of fundamental couplings and dynamical dark energy
Scalar field dynamics may give rise to a nonzero cosmological variation of
fundamental constants. Within different scenarios based on the unification of
gauge couplings, the various claimed observations and bounds may be combined in
order to trace or restrict the time history of the couplings and masses. If the
scalar field is responsible for a dynamical dark energy or quintessence,
cosmological information becomes available for its time evolution. Combining
this information with the time variation of couplings, one can determine the
interaction strength between the scalar and atoms, which may be observed by
tests of the Weak Equivalence Principle. We compute bounds on the present rate
of coupling variation from experiments testing the differential accelerations
for bodies with equal mass and different composition and compare the
sensitivity of various methods. In particular, we discuss two specific models
of scalar evolution: crossover quintessence and growing neutrino models.Comment: 26 pages, 2 figures; minor typos & added references, to be published
in JCA
Induced Gravity and the Attractor Dynamics of Dark Energy/Dark Matter
Attractor solutions that give dynamical reasons for dark energy to act like
the cosmological constant, or behavior close to it, are interesting
possibilities to explain cosmic acceleration. Coupling the scalar field to
matter or to gravity enlarges the dynamical behavior; we consider both
couplings together, which can ameliorate some problems for each individually.
Such theories have also been proposed in a Higgs-like fashion to induce gravity
and unify dark energy and dark matter origins. We explore restrictions on such
theories due to their dynamical behavior compared to observations of the cosmic
expansion. Quartic potentials in particular have viable stability properties
and asymptotically approach general relativity.Comment: 11 pages, 10 figures, accepted in JCAP, results unchanged, an
explanation added on perfect fluids for general spinor Lagrangian
The energy production rate & the generation spectrum of UHECRs
We derive simple analytic expressions for the flux and spectrum of ultra-high
energy cosmic-rays (UHECRs) predicted in models where the CRs are protons
produced by extra-Galactic sources. For a power-law scaling of the CR
production rate with redshift and energy, d\dot{n} /dE\propto E^-\alpha
(1+z)^m, our results are accurate at high energy, E>10^18.7 eV, to better than
15%, providing a simple and straightforward method for inferring d\dot{n}/dE
from the observed flux at E. We show that current measurements of the UHECR
spectrum, including the latest Auger data, imply
E^2d\dot{n}/dE(z=0)=(0.45\pm0.15)(\alpha-1) 10^44 erg Mpc^-3 yr^-1 at E<10^19.5
eV with \alpha roughly confined to 2\lesseq\alpha<2.7. The uncertainty is
dominated by the systematic and statistic errors in the experimental
determination of individual CR event energy, (\Delta E/E)_{sys} (\Delta
E/E)_{stat} ~20%. At lower energy, d\dot{n}/dE is uncertain due to the unknown
Galactic contribution. Simple models in which \alpha\simeq 2 and the transition
from Galactic to extra-Galactic sources takes place at the "ankle", E ~10^19
eV, are consistent with the data. Models in which the transition occurs at
lower energies require a high degree of fine tuning and a steep spectrum,
\alpha\simeq 2.7, which is disfavored by the data. We point out that in the
absence of accurate composition measurements, the (all particle) energy
spectrum alone cannot be used to infer the detailed spectral shapes of the
Galactic and extra-Galactic contributions.Comment: 9 pages, 11 figures, minor revision
Investigation of the high momentum component of nuclear wave function using hard quasielastic A(p,2p)X reactions
We present theoretical analysis of the first data on the high energy and
momentum transfer (hard) quasielastic reactions. The cross section
of hard reaction is calculated within the light-cone impulse
approximation based on two-nucleon correlation model for the high-momentum
component of the nuclear wave function. The nuclear effects due to modification
of the bound nucleon structure, soft nucleon-nucleon reinteraction in the
initial and final states of the reaction with and without color coherence have
been considered. The calculations including these nuclear effects show that the
distribution of the bound proton light-cone momentum fraction shifts
towards small values (), effect which was previously derived only
within plane wave impulse approximation. This shift is very sensitive to the
strength of the short range correlations in nuclei. Also calculated is an
excess of the total longitudinal momentum of outgoing protons. The calculations
are compared with data on the reaction obtained from the EVA/AGS
experiment at Brookhaven National Laboratory. These data show -shift in
agreement with the calculations. The comparison allows also to single out the
contribution from short-range nucleon correlations. The obtained strength of
the correlations is in agreement with the values previously obtained from
electroproduction reactions on nuclei.Comment: 30 pages LaTex file and 19 eps figure
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