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Search Results: 1 - 10 of 1324 matches for " Manoj Kaplinghat "
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Applications of High Resolution High Sensitivity Observations of the CMB
Manoj Kaplinghat
Physics , 2003, DOI: 10.1016/j.newar.2003.09.027
Abstract: With WMAP putting the phenomenological standard model of cosmology on a strong footing, one can look forward to mining the cosmic microwave background (CMB) for fundamental physics with higher sensitivity and on smaller scales. Future CMB observations have the potential to measure absolute neutrino masses, test for cosmic acceleration independent of supernova Ia observations, probe for the presence of dark energy at redshifts of 2 and larger, illuminate the end of the dark ages, measure the scale--dependence of the primordial power spectrum and detect gravitational waves generated by inflation.
Dark Energy and Neutrino Masses from Future Measurements of the Expansion History and Growth of Structure
Shahab Joudaki,Manoj Kaplinghat
Physics , 2011, DOI: 10.1103/PhysRevD.86.023526
Abstract: We forecast the expected cosmological constraints from a combination of probes of both the universal expansion rate and matter perturbation growth, in the form of weak lensing tomography, galaxy tomography, supernovae, and the cosmic microwave background incorporating all cross-correlations between the observables for an extensive cosmological parameter set. We allow for non-zero curvature and parameterize our ignorance of the early universe by allowing for a non-negligible fraction of dark energy (DE) at high redshifts. We find that early DE density can be constrained to 0.2% of the critical density of the universe with Planck combined with a ground-based LSST-like survey, while curvature can be constrained to 0.06%. However, these additional degrees of freedom degrade our ability to measure late-time dark energy and the sum of neutrino masses. We find that the combination of cosmological probes can break degeneracies and constrain the sum of neutrino masses to 0.04 eV, present DE density also to 0.2% of the critical density, and the equation of state to 0.01 - roughly a factor of two degradation in the constraints overall compared to the case without allowing for early DE. The constraints for a space-based mission are similar. Even a modest 1% dark energy fraction of the critical density at high redshift, if not accounted for in future analyses, biases the cosmological parameters by up to 2 sigma. Our analysis suggests that throwing out nonlinear scales (multipoles > 1000) may not result in significant degradation in future parameter measurements when multiple cosmological probes are combined. We find that including cross-correlations between the different probes can result in improved constraints by up to a factor of 2 for the sum of neutrino masses and early dark energy density.
Primeval Corrections to the CMB Anisotropies
Nemanja Kaloper,Manoj Kaplinghat
Physics , 2003, DOI: 10.1103/PhysRevD.68.123522
Abstract: We show that deviations of the quantum state of the inflaton from the thermal vacuum of inflation may leave an imprint in the CMB anisotropies. The quantum dynamics of the inflaton in such a state produces corrections to the inflationary fluctuations, which may be observable. Because these effects originate from IR physics below the Planck scale, they will dominate over any trans-Planckian imprints in any theory which obeys decoupling. Inflation sweeps away these initial deviations and forces its quantum state closer to the thermal vacuum. We view this as the quantum version of the cosmic no-hair theorem. Such imprints in the CMB may be a useful, independent test of the duration of inflation, or of significant features in the inflaton potential about 60 e-folds before inflation ended, instead of an unlikely discovery of the signatures of quantum gravity. The absence of any such substructure would suggest that inflation lasted uninterrupted much longer than ${\cal O}(100)$ e-folds.
How Cold Dark Matter Theory Explains Milgrom's Law
Manoj Kaplinghat,Michael S. Turner
Physics , 2001, DOI: 10.1086/340578
Abstract: Milgrom noticed the remarkable fact that the gravitational effect of dark matter in galaxies only becomes important where accelerations are less than about 10^{-8} cm s^{-2} ~ cH_0. This forms the basis for his Modified Newtonian Dynamics (MOND), an alternative to particle dark matter. However, any successful theory of galactic dynamics must account for Milgrom's Law. We show how Milgrom's Law comes about in the Cold Dark Matter (CDM) theory of structure formation.
Testing The Friedmann Equation: The Expansion of the Universe During Big-Bang Nucleosynthesis
Sean M. Carroll,Manoj Kaplinghat
Physics , 2001, DOI: 10.1103/PhysRevD.65.063507
Abstract: In conventional general relativity, the expansion rate H of a Robertson-Walker universe is related to the energy density by the Friedmann equation. Aside from the present day, the only epoch at which we can constrain the expansion history in a model-independent way is during Big-Bang Nucleosynthesis (BBN). We consider a simple two-parameter characterization of the behavior of H during BBN and derive constraints on this parameter space, finding that the allowed region of parameter space is essentially one-dimensional. We also study the effects of a large neutrino asymmetry within this framework. Our results provide a simple way to compare an alternative cosmology to the observational requirement of matching the primordial abundances of the light elements.
Inflation that runs naturally: Gravitational waves and suppression of power at large and small scales
Quinn E. Minor,Manoj Kaplinghat
Physics , 2014, DOI: 10.1103/PhysRevD.91.063504
Abstract: We point out three correlated predictions of the axion monodromy inflation model: large amplitude of gravitational waves, suppression of power on horizon scales and on scales relevant for the formation of dwarf galaxies. While these predictions are likely generic to models with oscillations in the inflaton potential, the axion monodromy model naturally accommodates the required running spectral index through Planck-scale corrections to the inflaton potential. Applying this model to a combined data set of Planck, ACT, SPT, and WMAP low-$\ell$ polarization cosmic microwave background (CMB) data, we find a best-fit tensor-to-scalar ratio $r_{0.05} = 0.07^{+0.05}_{-0.04}$ due to gravitational waves, which may have been observed by the BICEP2 experiment. Despite the contribution of gravitational waves, the total power on large scales (CMB power spectrum at low multipoles) is lower than the standard $\Lambda$CDM cosmology with a power-law spectrum of initial perturbations and no gravitational waves, thus mitigating some of the tension on large scales. There is also a reduction in the matter power spectrum of 20-30\% at scales corresponding to $k = 10~{\rm Mpc}^{-1}$, which are relevant for dwarf galaxy formation. This will alleviate some of the unsolved small-scale structure problems in the standard $\Lambda$CDM cosmology. The inferred matter power spectrum is also found to be consistent with recent Lyman-$\alpha$ forest data, which is in tension with the Planck-favored $\Lambda$CDM model with power-law primordial power spectrum.
Detection of a Gamma-Ray Source in the Galactic Center Consistent with Extended Emission from Dark Matter Annihilation and Concentrated Astrophysical Emission
Kevork N. Abazajian,Manoj Kaplinghat
Physics , 2012, DOI: 10.1103/PhysRevD.86.083511
Abstract: We show the existence of a statistically significant, robust detection of a gamma-ray source in the Milky Way Galactic Center that is consistent with a spatially extended signal using about 4 years of Fermi-LAT data. The gamma-ray flux is consistent with annihilation of dark matter particles with a thermal annihilation cross-section if the spatial distribution of dark matter particles is similar to the predictions of dark matter only simulations. We find statistically significant detections of an extended source with gamma-ray spectrum that is consistent with dark matter particle masses of approximately 10 GeV to 1 TeV annihilating to b/b-bar quarks, and masses approximately 10 GeV to 30 GeV annihilating to tau+ tau- leptons. However, a part of the allowed region in this interpretation is in conflict with constraints from Fermi observations of the Milky Way satellites. The biggest improvement over the fit including just the point sources is obtained for a 30 GeV dark matter particle annihilating to b/b-bar quarks. The gamma-ray intensity and spectrum are also well fit with emission from a millisecond pulsar (MSP) population following a density profile like that of low-mass X-ray binaries observed in M31. The greatest goodness-of-fit of the extended emission is with spectra consistent with known astrophysical sources like MSPs in globular clusters or cosmic ray bremsstrahlung on molecular gas. Therefore, we conclude that the bulk of the emission is likely from an unresolved or spatially extended astrophysical source. However, the interesting possibility of all or part of the extended emission being from dark matter annihilation cannot be excluded at present.
Rapid Calculation of Theoretical CMB Angular Power Spectra
Manoj Kaplinghat,Lloyd Knox,Constantinos Skordis
Physics , 2002, DOI: 10.1086/342656
Abstract: We have developed a fast method for predicting the angular power spectrum, C_l, of the cosmic microwave background given cosmological parameters and a primordial power spectrum of perturbations. After pre--computing the radiation temperature and gravitational potential transfer functions over a small sub--space of the total model parameter space, the rest of the model space (six or more cosmological parameters and arbitrarily many primordial power spectrum parameters) is reached via rapid analytic and semi--analytic approximations which are highly accurate on all angular scales for which linear perturbation theory applies. A single power spectrum can be calculated in ~ 1 second on a desktop computer. We discuss applications to cosmological parameter estimation.
Normal Parameters for an Analytic Description of the CMB Cosmological Parameter Likelihood
Mike Chu,Manoj Kaplinghat,Lloyd Knox
Physics , 2002, DOI: 10.1086/378039
Abstract: The normal parameters are a non--linear transformation of the cosmological parameters whose likelihood function is very well--approximated by a normal distribution. This transformation serves as an extreme form of data compression allowing for practically instantaneous calculation of the likelihood of any given model, as long as the model is in the parameter space originally considered. The compression makes all the information about cosmological parameter constraints from a given set of experiments available in a useable manner. Here we explicitly define the normal parameters that work for the current CMB data, and give their mean and covariance matrix which best fit the likelihood function calculated by the Monte Carlo Markov Chain method. Along with standard parameter estimation results, we propose that future CMB parameter analyses define normal parameters and quote their mean and covariance matrix.
Solving the Coincidence Problem: Tracking Oscillating Energy
Scott Dodelson,Manoj Kaplinghat,Ewan Stewart
Physics , 2000, DOI: 10.1103/PhysRevLett.85.5276
Abstract: Recent cosmological observations strongly suggest that the universe is dominated by an unknown form of energy with negative pressure. Why is this dark energy density of order the critical density today? We propose that the dark energy has periodically dominated in the past so that its preponderance today is natural. We illustrate this paradigm with a model potential and show that its predictions are consistent with all observations.
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