44 research outputs found
Squark-, Slepton- and Neutralino-Chargino coannihilation effects in the low-energy effective MSSM
Within the low-energy effective Minimal Supersymmetric extension of the
Standard Model (effMSSM) we calculate the neutralino relic density taking into
account slepton-neutralino, squark-neutralino and neutralino/chargino-
neutralino coannihilation channels. By including squark (stop and sbottom)
coannihilation channels we extend our comparative study to all allowed
coannihilations and obtain the general result that all of them give sizable
contributions to the reduction of the neutralino relic density. Due to these
coannihilation processes some models (mostly with large neutralino masses)
enter into the cosmologically interesting region for relic density, but other
models leave this region. Nevertheless, in general, the predictions for direct
and indirect dark matter detection rates are not strongly affected by these
coannihilation channels in the effMSSM.Comment: 14 pages, 10 figures, corrected and to be published in Phys. Rev.
Cosmic Density Perturbations from Late-Decaying Scalar Condensations
We study the cosmic density perturbations induced from fluctuation of the
amplitude of late-decaying scalar condensations (called \phi) in the scenario
where the scalar field \phi once dominates the universe. In such a scenario,
the cosmic microwave background (CMB) radiation originates to decay products of
the scalar condensation and hence its anisotropy is affected by the fluctuation
of \phi. It is shown that the present cosmic density perturbations can be
dominantly induced from the primordial fluctuation of \phi, not from the
fluctuation of the inflaton field. This scenario may change constraints on the
source of the density perturbations, like inflation. In addition, a correlated
mixture of adiabatic and isocurvature perturbations may arise in such a
scenario; possible signals in the CMB power spectrum are discussed. We also
show that the simplest scenario of generating the cosmic density perturbations
only from the primordial fluctuation of \phi (i.e., so-called ``curvaton''
scenario) is severely constrained by the current measurements of the CMB
angular power spectrum if correlated mixture of the adiabatic and isocurvature
perturbations are generated.Comment: 31pages, 14figure
Current constraints on Cosmological Parameters from Microwave Background Anisotropies
We compare the latest observations of Cosmic Microwave Background (CMB)
Anisotropies with the theoretical predictions of the standard scenario of
structure formation. Assuming a primordial power spectrum of adiabatic
perturbations we found that the total energy density is constrained to be
while the energy density in baryon and Cold Dark
Matter (CDM) are and ,
(all at 68% C.L.) respectively. The primordial spectrum is consistent with
scale invariance, () and the age of the universe is
Gyrs. Adding informations from Large Scale Structure and
Supernovae, we found a strong evidence for a cosmological constant
and a value of the Hubble parameter
. Restricting this combined analysis to flat universes, we put
constraints on possible 'extensions' of the standard scenario. A gravity waves
contribution to the quadrupole anisotropy is limited to be (95%
c.l.). A constant equation of state for the dark energy component is bound to
be (95% c.l.). We constrain the effective relativistic degrees
of freedom and the neutrino chemical potential and (massless neutrinos).Comment: The status of cosmological parameters before WMAP. In press on Phys.
Rev. D., Rapid Communication, 6 pages, 5 figure
Big Bang nucleosynthesis and cosmic microwave background constraints on the time variation of the Higgs vacuum expectation value
We derive constraints on the time variation of the Higgs vacuum expectation
value through the effects on Big Bang nucleosynthesis (BBN) and the
cosmic microwave background (CMB). In the former case, we include the
(previously-neglected) effect of the change in the deuteron binding energy,
which alters both the He and deuterium abundances significantly. We find
that the current BBN limits on the relative change in \higgs are , where the
exact limits depend on the model we choose for the dependence of the deuteron
binding energy on \higgs.The limits from the current CMB data are much weaker.Comment: 5 pages including 5 figures, accepted for publication in Phys. Rev.
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum
P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in
combination with WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when
dropping prior assumptions about curvature, neutrinos, tensor modes and the
equation of state. Our results are in substantial agreement with the joint
analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive
consistency check with independent redshift survey data and analysis
techniques. In this paper, we place particular emphasis on clarifying the
physical origin of the constraints, i.e., what we do and do not know when using
different data sets and prior assumptions. For instance, dropping the
assumption that space is perfectly flat, the WMAP-only constraint on the
measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running
tilt, neutrino mass and equation of state in the list of free parameters, many
constraints are still quite weak, but future cosmological measurements from
SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm
The State of the Dark Energy Equation of State
By combining data from seven cosmic microwave background experiments
(including the latest WMAP results) with large scale structure data, the Hubble
parameter measurement from the Hubble Space Telescope and luminosity
measurements of Type Ia supernovae we demonstrate the bounds on the dark energy
equation of state to be at the 95% confidence level.
Although our limit on is improved with respect to previous analyses,
cosmological data does not rule out the possibility that the equation of state
parameter of the dark energy is less than -1. We present a tracking
model that ensures at recent times and discuss the observational
consequences.Comment: 7 pages, 4 figures, added a referenc
Inverse Power Law Quintessence with Non-Tracking Initial Conditions
A common property of popular models of quintessence dark energy is the
convergence to a common solution from a large range of the initial conditions.
We re-examine the popular inverse power-law model of quintessence (where the
common solution is dubbed as the 'tracker') with particular attention to the
initial conditions for the field and their influence on the evolution. We find
that previously derived limits on the parameters of the potential in this model
are valid only in a range of initial conditions. A reasonably sharp boundary
lies where the initial energy density of the scalar field is equal to that of
the background radiation component. An initial quintessence energy density
above this equipartition value lead to a solution that will not have joined the
tracker solution by the present epoch. These non-tracker solutions possess the
property that their present equation of state is very compatible with the
observed bounds and independent of the exponent of the potential.Comment: RevTEX4, 9 figure
Cosmological parameters from CMB and other data: a Monte-Carlo approach
We present a fast Markov Chain Monte-Carlo exploration of cosmological
parameter space. We perform a joint analysis of results from recent CMB
experiments and provide parameter constraints, including sigma_8, from the CMB
independent of other data. We next combine data from the CMB, HST Key Project,
2dF galaxy redshift survey, supernovae Ia and big-bang nucleosynthesis. The
Monte Carlo method allows the rapid investigation of a large number of
parameters, and we present results from 6 and 9 parameter analyses of flat
models, and an 11 parameter analysis of non-flat models. Our results include
constraints on the neutrino mass (m_nu < 0.3eV), equation of state of the dark
energy, and the tensor amplitude, as well as demonstrating the effect of
additional parameters on the base parameter constraints. In a series of
appendices we describe the many uses of importance sampling, including
computing results from new data and accuracy correction of results generated
from an approximate method. We also discuss the different ways of converting
parameter samples to parameter constraints, the effect of the prior, assess the
goodness of fit and consistency, and describe the use of analytic
marginalization over normalization parameters.Comment: Quintessence results now include perturbations. Changes to match
version accepted by PRD. MCMC code and data are available at
http://cosmologist.info/cosmomc/ along with a B&W printer-friendly version of
the pape
Cosmological Constraints on Decaying Dark Matter
We present a complete analysis of the cosmological constraints on decaying
dark matter. Previous analyses have used the cosmic microwave background and
Type Ia supernova. We have updated them with the latest data as well as
extended the analysis with the inclusion of Lyman- forest, large scale
structure and weak lensing observations. Astrophysical constraints are not
considered in the present paper. The bounds on the lifetime of decaying dark
matter are dominated by either the late-time integrated Sachs-Wolfe effect for
the scenario with weak reionization, or CMB polarization observations when
there is significant reionization. For the respective scenarios, the lifetimes
for decaying dark matter are Gyr and Gyr (at 95.4% confidence level), where the
phenomenological parameter is the fraction of the decay energy deposited in
baryonic gas. This allows us to constrain particle physics models with dark
matter candidates through investigation of dark matter decays into Standard
Model particles via effective operators. For decaying dark matter of
GeV mass, we found that the size of the coupling constant in the effective
dimension-4 operators responsible for dark matter decay has to generically be . We have also explored the implications of our analysis for
representative models in theories of gauge-mediated supersymmetry breaking,
minimal supergravity and little Higgs.Comment: 29 pages, 6 figures. Added references and corrected typos as well as
grammatical oversight
Polygenic risk scores for prediction of breast cancer risk in women of African ancestry: A cross-ancestry approach
Polygenic risk scores (PRSs) are useful for predicting breast cancer risk, but the prediction accuracy of existing PRSs in women of African ancestry (AA) remains relatively low. We aim to develop optimal PRSs for the prediction of overall and estrogen receptor (ER) subtype-specific breast cancer risk in AA women. The AA dataset comprised 9235 cases and 10 184 controls from four genome-wide association study (GWAS) consortia and a GWAS study in Ghana. We randomly divided samples into training and validation sets. We built PRSs using individual-level AA data by a forward stepwise logistic regression and then developed joint PRSs that combined (1) the PRSs built in the AA training dataset and (2) a 313-variant PRS previously developed in women of European ancestry. PRSs were evaluated in the AA validation set. For overall breast cancer, the odds ratio per standard deviation of the joint PRS in the validation set was 1.34 [95% confidence interval (CI): 1.27-1.42] with the area under receiver operating characteristic curve (AUC) of 0.581. Compared with women with average risk (40th-60th PRS percentile), women in the top decile of the PRS had a 1.98-fold increased risk (95% CI: 1.63-2.39). For PRSs of ER-positive and ER-negative breast cancer, the AUCs were 0.608 and 0.576, respectively. Compared with existing methods, the proposed joint PRSs can improve prediction of breast cancer risk in AA women