1,381 research outputs found
Inclusive Photoproduction of Polarized Quarkonium
We analyse inclusive photoproduction of polarized quarkonium in the
framework of QCD. To separate nonperturbative and perturbative parts in the
density matrix of the produced quarkonium we use a method , which is equivalent
to the diagramatic expansion widely used in analysing deeply inelastic
scatterings. A systematic expansion in a small velocity , with which a heavy
quark moves inside the quarkonium in its rest frame, is performed for the
nonperturbative parts, and they are expressed as matrix elements in
nonrelativistic QCD. At the leading order of there are four matrix elements
representing nonperturbative physics. The perturbative parts are calculated at
the leading order of coupling constants. Some numerical results, especially,
numerical results for HERA are given.Comment: 19 pages+7 Figures as one compressed and encoded postcript fil
DCC Dynamics in (2+1)D-O(3) model
The dynamics of symmetry-breaking after a quench is numerically simulated on
a lattice for the (2+1)-dimensional O(3) model. In addition to the standard
sigma-model with temperature-dependent Phi^4-potential the energy functional
includes a four-derivative current-current coupling to stabilize the size of
the emerging extended topological textures. The total winding number can be
conserved by constraint. As a model for the chiral phase transition during the
cooling phase after a hadronic collision this allows to investigate the
interference of 'baryon-antibaryon' production with the developing disoriented
aligned domains. The growth of angular correlations, condensate, average
orientation is studied in dependence of texture size, quench rate, symmetry
breaking. The classical dissipative dynamics determines the rate of energy
emitted from the relaxing source for each component of the 3-vector field which
provides a possible signature for domains of Disoriented Chiral Condensate. We
find that the 'pions' are emitted in two distinct pulses; for sufficiently
small lattice size the second one carries the DCC signal, but it is strongly
suppressed as compared to simultaneous 'sigma'-meson emission. We compare the
resulting anomalies in the distributions of DCC pions with probabilities
derived within the commonly used coherent state formalism.Comment: 27 pages, 17 figures; several minor insertions in the text; two
references adde
Cosmological implications of a light dilaton
Supersymmetric Peccei-Quinn symmetry and string theory predict a complex
scalar field comprising a dilaton and an axion. These fields are massless at
high energies, but it is known since long that the axion is stabilized in an
instanton dominated vacuum. Instantons and axions together also provide a
mechanism to stabilize a dilaton, thus accounting for a dilaton as a possible
cold dark matter component accompanying the axion. We briefly review the
prospects of this scenario and point out further implications.Comment: LaTeX, 9 pages incl. 1 figure, reference adde
Exact Solutions of Model Hamiltonian Problems with Effective Interactions
We demonstrate with soluble models how to employ the effective Hamiltonian
approach of Lee and Suzuki to obtain all the exact eigenvalues of the full
Hamiltonian. We propose a new iteration scheme to obtain the effective
Hamiltonian and demonstrate its convergence properties.Comment: 12 pages and 1 figur
Constrained Supersymmetric Flipped SU(5) GUT Phenomenology
We explore the phenomenology of the minimal supersymmetric flipped SU(5) GUT
model (CFSU(5)), whose soft supersymmetry-breaking (SSB) mass parameters are
constrained to be universal at some input scale, , above the GUT scale,
. We analyze the parameter space of CFSU(5) assuming that the lightest
supersymmetric particle (LSP) provides the cosmological cold dark matter,
paying careful attention to the matching of parameters at the GUT scale. We
first display some specific examples of the evolutions of the SSB parameters
that exhibit some generic features. Specifically, we note that the relationship
between the masses of the lightest neutralino and the lighter stau is sensitive
to , as is the relationship between the neutralino mass and the masses
of the heavier Higgs bosons. For these reasons, prominent features in generic
planes such as coannihilation strips and rapid-annihilation
funnels are also sensitive to , as we illustrate for several cases with
tan(beta)=10 and 55. However, these features do not necessarily disappear at
large , unlike the case in the minimal conventional SU(5) GUT. Our
results are relatively insensitive to neutrino masses.Comment: 23 pages, 8 figures; (v2) added explanations and corrected typos,
version to appear in EPJ
Likelihood Functions for Supersymmetric Observables in Frequentist Analyses of the CMSSM and NUHM1
On the basis of frequentist analyses of experimental constraints from
electroweak precision data, g-2, B physics and cosmological data, we
investigate the parameters of the constrained MSSM (CMSSM) with universal soft
supersymmetry-breaking mass parameters, and a model with common non-universal
Higgs masses (NUHM1). We present chi^2 likelihood functions for the masses of
supersymmetric particles and Higgs bosons, as well as b to s gamma, b to mu mu
and the spin-independent dark matter scattering cross section. In the CMSSM we
find preferences for sparticle masses that are relatively light. In the NUHM1
the best-fit values for many sparticle masses are even slightly smaller, but
with greater uncertainties. The likelihood functions for most sparticle masses
are cut off sharply at small masses, in particular by the LEP Higgs mass
constraint. Both in the CMSSM and the NUHM1, the coannihilation region is
favoured over the focus-point region at about the 3-sigma level, largely but
not exclusively because of g-2. Many sparticle masses are highly correlated in
both the CMSSM and NUHM1, and most of the regions preferred at the 95% C.L. are
accessible to early LHC running. Some slepton and chargino/neutralino masses
should be in reach at the ILC. The masses of the heavier Higgs bosons should be
accessible at the LHC and the ILC in portions of the preferred regions in the
(M_A, tan beta) plane. In the CMSSM, the likelihood function for b to mu mu is
peaked close to the Standard Model value, but much larger values are possible
in the NUHM1. We find that values of the DM cross section > 10^{-10} pb are
preferred in both the CMSSM and the NUHM1. We study the effects of dropping the
g-2, b to s gamma, relic density and M_h constraints.Comment: 34 pages, 24 figure
Experimental determination of the effective strong coupling constant
We present a first attempt to experimentally extract an effective strong
coupling constant that we define to be a low Q2 extension of a previous
definition by S. Brodsky et al. following an initial work of G. Grunberg. Using
Jefferson Lab data and sum rules, we establish its Q2-behavior over the
complete Q2-range. The result is compared to effective coupling constants
inferred from different processes and to calculations based on Schwinger-Dyson
equations, hadron spectroscopy or lattice QCD. Although the connection between
the experimentally extracted effective coupling constants and the calculations
is not established it is interesting to note that their behaviors are similar.Comment: Published in Physics Letters B 650 4 24
Formation of extended topological defects during symmetry breaking phase transitions in O(2) and O(3) models
The density of extended topological defects created during symmetry-breaking
phase transitions depends on the ratio between the correlation length in the
symmetric phase near and the winding length of the defects as determined
by the momentaneous effective action after a typical relaxation time.
Conservation of winding number in numerical simulations requires a suitable
embedding of the field variables and the appropriate geometrical implementation
of the winding density on the discrete lattice. We define a modified Kibble
limit for the square lattice and obtain defect densities as functions of
winding lengths in O(2) and O(3) models. The latter allows to observe formation
of disoriented aligned domains within the easy plane. Their extent is severely
limited by the momentaneous defect density during the course of the quench.Comment: 16 pages, 9 figure
Perturbative Prediction for Parton Fragmentation into Heavy Hadron
By expanding functions of parton fragmentation into a heavy hadron in the
inverse of the heavy quark mass we attempt to factorize them into
perturbative- and nonperturbative parts. In our approach the nonperturbative
parts can be defined as matrix elements in heavy quark effective theory, the
shape of the functions is predicted by perturbative QCD. In this work we
neglect effect at order of and calculate the perturbative parts at
one-loop level for heavy quark- and gluon fragmentation. We compare our results
from leading log approximation with experimental results from
colliders and find a deviation below or at 10% level. Adding effect of higher
order in it can be expected to reduce the deviation. The size of
matrix elements appearing at the order we consider for several types of heavy
hadrons is determined.Comment: 21 pages + 3 pages figures, plain te
Phenomenology of GUT-less Supersymmetry Breaking
We study models in which supersymmetry breaking appears at an intermediate
scale, M_{in}, below the GUT scale. We assume that the soft
supersymmetry-breaking parameters of the MSSM are universal at M_{in}, and
analyze the morphology of the constraints from cosmology and collider
experiments on the allowed regions of parameter space as M_{in} is reduced from
the GUT scale. We present separate analyses of the (m_{1/2},m_0) planes for
tan(beta)=10 and tan(beta)=50, as well as a discussion of non-zero trilinear
couplings, A_0. Specific scenarios where the gaugino and scalar masses appear
to be universal below the GUT scale have been found in mirage-mediation models,
which we also address here. We demand that the lightest neutralino be the LSP,
and that the relic neutralino density not conflict with measurements by WMAP
and other observations. At moderate values of M_{in}, we find that the allowed
regions of the (m_{1/2},m_0) plane are squeezed by the requirements of
electroweak symmetry breaking and that the lightest neutralino be the LSP,
whereas the constraint on the relic density is less severe. At very low M_{in},
the electroweak vacuum conditions become the dominant constraint, and a
secondary source of astrophysical cold dark matter would be necessary to
explain the measured relic density for nearly all values of the soft
SUSY-breaking parameters and tan(beta). We calculate the neutralino-nucleon
cross sections for viable scenarios and compare them with the present and
projected limits from direct dark matter searches.Comment: 35 pages, 9 figures; typos corrected, references adde
- …