|
| |
arXiv:0801.0642 [ps, pdf, other] :
Title: Correlation of CMB with large-scale structure: I. ISW Tomography and Cosmological Implications
Authors: Shirley Ho, Christopher M. Hirata, Nikhil Padmanabhan, Uros Seljak, Neta Bahcall
Comments: 35 pages, 18 figures, to be submitted to PRD. The likelihood code can be downloaded at this http URL
We cross-correlate large scale structure (LSS) observations from a number of surveys with CMB anisotropies from WMAP to investigate the Integrated Sachs-Wolfe (ISW) effect as a function of redshift, covering z~0.1-2.5. Our main goal is to go beyond reporting detections towards developing a reliable likelihood analysis that allows one to determine cosmological constraints from ISW observations. With this in mind we spend a considerable amount of effort in determining the redshift-dependent bias and redshift distribution b(z)*dN/dz of these samples by matching with spectroscopic observations where available, and analyzing auto-power spectra and cross-power spectra between the samples. The data sets we use are 2-Micron All Sky Survey (2MASS) samples, Sloan Digital Sky Survey (SDSS) photometric Luminous Red Galaxies, SDSS photometric quasars and NRAO VLA Sky Survey (NVSS) radio sources. We make a joint analysis of all samples constructing a full covariance matrix, which we subsequently use for cosmological parameter fitting. We report a 3.7 sigma detection of ISW combining all the datasets. We combine the ISW likelihood function with weak lensing of CMB and CMB power spectrum to constrain the equation of state of dark energy and the curvature of the Universe. While ISW does not significantly improve the constraints in the simplest 6-parameter flat Lambda CDM model, it improves constraints on 7-parameter models with curvature by a factor of 2.5 (relative to WMAP alone) to Omega_K=-0.006^+0.017_-0.028, and with dark energy equation of state by 15% to w=-1.01^{+0.37}_{-0.40}. (Abridged.) |
| |
|
arXiv:0801.1232 [ps, pdf, other] :
Title: The Milky Way's Rotation Curve to 60 kpc and an Estimate of the Dark Matter Halo Mass from Kinematics of ~2500 SDSS Blue Horizontal Branch Stars
Authors: X.-X. Xue et al.
Comments: 38 pages, 16 figures and 1 table. Submitted to ApJ
We derive new constraints on the mass of the Milky Way's dark matter halo, based on a set of halo stars from SDSS DR-6 as kinematic tracers. Our sample contains 2466 rigorously selected Blue Horizontal-Branch (BHB) halo stars distances from the Galactic center up to ~60 kpc. This sample enables construction of the full line-of-sight velocity distribution at different Galactocentric radii. To interpret these distributions, we compare them to matched mock observations drawn from two different cosmological galaxy formation simulations designed to resemble the Milky Way. Specifically, we select simulated halo stars in the same volume as the observations, and derive the distributions P(V_{l.o.s}/V_{cir}) of their line-of-sight velocities for different radii, normalized by the simulation's local circular velocity. We then determine which value of V_{cir}(r) brings the observed distribution into agreement with the corresponding distributions from the simulations; these values as adopted as observational estimates for V_{cir}(r) in the Milky Way's halo. This procedure results in an estimate of the Milky Way rotation curve to ~60 kpc, which is found to be slightly falling and implies M$_{\rm vir}=1.1\pm 0.2 \times 10^{12}$M$_\odot$. The radial dependence of the circular velocity is found to be consistent with the expectations from an NFW dark matter halo with the established stellar mass components at its center. If we assume an NFW halo profile of characteristic concentration holds, we can estimate the virial mass of the Milky Way's dark matter halo, M$_{vir}=1.1\pm 0.2 \times 10^{12}$M$_\odot$. This estimate implies that nearly 40% of the baryons within the virial radius of the Milky Way's dark matter halo reside in the stellar components of our Galaxy. |
| |
|
arXiv:0801.1315 [ps, pdf, other] :
Title: The Hagedorn Soup and an Emergent Cyclic Universe
Authors: Tirthabir Biswas
Comments: 15 pages, 1 figure
One of the problems of constructing a successful cyclic universe scenario is that it has to incorporate the second law of thermodynamics. This leads to Tolman's ever shrinking cycles which eventually vanish at a finite proper time in the past. In this paper we construct a theoretically consistent (ghost-free) non-singular toy model where as the cycles shrink in the past they also spend more and more time in the Hagedorn phase where all the string states are in thermal equilibrium and entropy is conserved. Thus in such a scenario the entropy asymptotes to a finite non-zero constant in the infinite past. The universe ``emerges'' from a small (string size) geodesically complete quasi-periodic space-time. This paradigm also naturally addresses some of the classic puzzles of Big Bang cosmology, such as the largeness, horizon and flatness problems. |
| |
|
arXiv:0801.0607 [ps, pdf, other] :
Title: Impact of massive neutrinos on nonlinear matter power spectrum
Authors: Shun Saito, Masahiro Takada, Atsushi Taruya
Comments: 5 pages, 2 figures
We present an approach to describe the nonlinear matter power spectrum for a mixed dark matter (cold dark matter plus neutrinos having total mass of ~0.1eV) model based on cosmological perturbation theory. The suppression of the power spectrum amplitude caused by massive neutrinos is enhanced in the weakly nonlinear regime where standard linear theory ceases to be accurate. Due to this enhanced effect and the gain in the applicable range of the model prediction, the nonlinear model may enable a precision of sigma(m_tot)~0.09eV in constraining the total neutrino mass for the planned galaxy redshift survey, a factor 2.5 improvement compared to the linear regime. The refined model prescription thus offers a vital opportunity to determine the neutrino masses. |
| |
|
arXiv:0712.4146 [ps, pdf, other] :
Title: Mixed Sneutrinos, Dark Matter and the LHC
Authors: Zachary Thomas, David Tucker-Smith, Neal Weiner
Comments: -
We study the phenomenology of supersymmetric models in which gauge-singlet scalars mix with the MSSM sneutrinos through weak-scale $A$ terms. After reviewing the constraints on mixed-sneutrino dark matter from measurements of $\Omega_{CDM}$ and from direct-detection experiments, we explore mixed-sneutrino signatures relevant to the LHC. For a mixed-sneutrino LSP and a right-handed slepton NLSP, decays of the lightest neturalino can produce opposite-sign, same-flavor (OSSF) dileptons with an invariant-mass distribution shifted away from the kinematic endpoint. In different parameter regions, the charginos and neutralinos produced in cascades all decay dominantly to the lighter sneutrinos, leading to a kinematic edge in the jet-lepton invariant-mass distribution from the decay chain $\tilde{q} \to \chi^- q \to \snu^* l q$, without an OSSF dilepton signature. We explore the possibility of using mass estimation methods to distinguish this mixed-sneutrino jet-lepton signature from an MSSM one. Finally, we consider signatures associated with Higgs-lepton or $Z$-lepton production in cascades involving the heavier sneutrinos. |
| |
|
arXiv:0712.0618 [ps, pdf, other] :
Title: Precision of Hubble constant derived using black hole binary absolute distances and statistical redshift information
Authors: Chelsea L. MacLeod, Craig J. Hogan
Comments: 9 pages, 4 figures, submitted to Phys. Rev. D
Measured gravitational waveforms from black hole binary inspiral events directly determine absolute luminosity distances. To use these data for cosmology, it is necessary to independently obtain redshifts for the events, which may be difficult for those without electromagnetic counterparts. Here it is demonstrated that certainly in principle, and possibly in practice, clustering of galaxies allows extraction of the redshift information from a sample statistically for the purpose of estimating mean cosmological parameters, without identification of host galaxies for individual events. We extract mock galaxy samples from the 6th Data Release of the Sloan Digital Sky Survey resembling those that would be associated with inspiral events of stellar mass black holes falling into massive black holes at redshift z ~ 0.1 to 0.5. A simple statistical procedure is described to estimate a likelihood function for the Hubble constant H_0: each galaxy in a LISA error volume contributes linearly to the log likelihood for the source redshift, and the log likelihood for each source contributes linearly to that of H_0. This procedure is shown to provide an accurate and unbiased estimator of H_0. It is estimated that a precision better than one percent in H_0 may be possible if the rate of such events is sufficiently high, on the order of 20 to z = 0.5. |
| |
|
arXiv:0712.1250 [ps, pdf, other] :
Title: Gravitational Wave Detection with Atom Interferometry
Authors: Savas Dimopoulos, Peter W. Graham, Jason M. Hogan, Mark A. Kasevich, Surjeet Rajendran
Comments: 5 pages, 5 figures
We propose two distinct atom interferometer gravitational wave detectors, one terrestrial and another satellite-based, utilizing the core technology of the Stanford 10 m atom interferometer presently under construction. The terrestrial experiment can operate with strain sensitivity ~10^{-19}/sqrt{Hz} in the 1 Hz - 10 Hz band, inaccessible to LIGO, and can detect gravitational waves from solar mass binaries out to megaparsec distances. The satellite experiment probes the same frequency spectrum as LISA with better strain sensitivity ~10^{-20}/sqrt{Hz}. Each configuration compares two widely separated atom interferometers run using common lasers. The effect of the gravitational waves on the propagating laser field produces the main effect in this configuration and enables a large enhancement in the gravitational wave signal while significantly suppressing many backgrounds. The use of ballistic atoms (instead of mirrors) as inertial test masses improves systematics coming from vibrations and acceleration noise, and reduces spacecraft control requirements. |
| |
|
arXiv:0712.1147 [ps, pdf, other] :
Title: Upper limit on the cosmic-ray photon flux above 10^19 eV using the surface detector of the Pierre Auger Observatory
Authors: Pierre Auger Collaboration
Comments: 28 pages, 9 figures
A method is developed to search for air showers initiated by photons using data recorded by the surface detector of the Auger Observatory. The approach is based on observables sensitive to the longitudinal shower development, the signal risetime and the curvature of the shower front. Applying this method to the data, upper limits on the flux of photons of 3.8*10^-3, 2.5*10^-3, and 2.2*10^-3 km^-2 sr^-1 yr^-1 above 10^19 eV, 2*10^19 eV, and 4*10^19 eV are derived, with corresponding limits on the fraction of photons being 2.0%, 5.1%, and 31% (all limits at 95% c.l.). These photon limits disfavor certain exotic models of sources of cosmic rays. The results also show that the approach adopted by the Auger Observatory to calibrate the shower energy is not strongly biased by a contamination from photons. |
| |
|
| |
| |
| |
| |
| |
| |
| |
| |
|
