A5011447076- Cosmology and Gravitation Theories
- Dark Matter and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Particle physics theoretical and experimental studies
- Pulsars and Gravitational Waves Research
- Astronomy and Astrophysical Research
- Black Holes and Theoretical Physics
- Geophysics and Gravity Measurements
- Stellar, planetary, and galactic studies
- Solar and Space Plasma Dynamics
- Relativity and Gravitational Theory
- Scientific Research and Discoveries
- Neutrino Physics Research
- Gamma-ray bursts and supernovae
- History and Developments in Astronomy
- Computational Physics and Python Applications
- Atomic and Subatomic Physics Research
- Astrophysics and Star Formation Studies
- Astrophysical Phenomena and Observations
- Adaptive optics and wavefront sensing
- Superconducting and THz Device Technology
- Mechanics and Biomechanics Studies
- Space Science and Extraterrestrial Life
Johns Hopkins University
2016-2025
Ben-Gurion University of the Negev
2023
University of Baltimore
2022
Istituto Nazionale di Fisica Nucleare, Sezione di Trieste
2021
University of Trieste
2021
ORCID
2019
Bloomberg (United States)
2012-2014
University of Chicago
1989-2014
McGill University
2014
California Institute of Technology
2003-2012
There is almost universal agreement among astronomers that most of the mass in Universe and Galactic halo dark. Many lines reasoning suggest dark matter consists some new, as yet undiscovered, weakly-interacting massive particle (WIMP). now a vast experimental effort being surmounted to detect WIMPS halo. The promising techniques involve direct detection low-background laboratory detectors indirect through observation energetic neutrinos from annihilation WIMPs have accumulated Sun and/or...
We explore the consequences that follow if dark energy is phantom energy, in which sum of pressure and density negative. The positive phantom-energy becomes infinite finite time, overcoming all other forms matter, such gravitational repulsion rapidly brings our brief epoch cosmic structure to a close. rips apart Milky Way, solar system, Earth, ultimately molecules, atoms, nuclei, nucleons we are composed, before death Universe "big rip."
We consider the possibility that black-hole (BH) binary detected by LIGO may be a signature of dark matter. Interestingly enough, there remains window for masses 20M_{⊙}≲M_{bh}≲100M_{⊙} where primordial black holes (PBHs) constitute If two BHs in galactic halo pass sufficiently close, they radiate enough energy gravitational waves to become gravitationally bound. The bound will rapidly spiral inward due emission radiation and ultimately merge. Uncertainties rate such events arise from our...
We present a formalism for analyzing full-sky temperature and polarization map of the cosmic microwave background. Temperature maps are analyzed by expanding over set spherical harmonics to give multipole moments two-point correlation function. Polarization, which is described second-rank tensor, can be treated analogously in appropriate tensor harmonics. provide expressions complete scalar metric perturbations. Four sets completely describe isotropic correlations; perturbations one...
Early dark energy (EDE) that behaves like a cosmological constant at early times (redshifts z≳3000) and then dilutes away radiation or faster later can solve the Hubble tension. In these models, sound horizon decoupling is reduced resulting in larger value of parameter H0 inferred from cosmic microwave background (CMB). We consider two physical models for this EDE, one involving an oscillating scalar field another slowly rolling field. perform detailed calculation evolution perturbations...
Using partial-wave unitarity and the observed density of Universe, we show that a stable elementary particle which was once in thermal equilibrium cannot have mass greater than 340 TeV. An extended object radius less 7.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ fm. A lower limit to relic abundance such particles is also found.
We consider the stochastic background of gravity waves produced by first-order cosmological phase transitions from two types sources: colliding bubbles and hydrodynamic turbulence. First we discuss fluid mechanics relativistic spherical combustion. then numerically collide many expanding at a velocity $v$ calculate resulting spectrum gravitational radiation in linearized approximation. Our results are expressed as simple functions mean bubble separation, expansion velocity, latent heat,...
A formalism for describing an all-sky map of the polarization cosmic microwave background is presented. The pattern on sky can be decomposed into two geometrically distinct components. One these components not coupled to density inhomogeneities. nonzero amplitude this component only caused by tensor or vector metric perturbations. This allows unambiguous identification long-wavelength gravity waves large-scale vortical flows at time last scattering.
We present new determinations of the cosmic expansion history from red-envelope galaxies. have obtained for this purpose high-quality spectra with Keck-LRIS spectrograph galaxies in 24 galaxy clusters redshift range 0.2 < z 1.0. complement these Keck high-quality, publicly available archival SPICES and VVDS surveys. improve over our previous measurements Simon et al. (2005) by providing two history: H(z) = 97 +- 62 km/sec/Mpc at 0.5 90 40 0.8. discuss uncertainty determination that arises...
Are there any manifestations of parity violation other than those observed in weak interactions? A map the cosmic microwave background (CMB) temperature and polarization will provide a new signature $P$ violation. We examine two classes $P$-violating interactions that would give rise to such signature. The first interaction leads cosmological birefringence, possibly driven by quintessence. an asymmetry amplitude right- versus left-handed gravitational waves produced during inflation. Planck...
We review and analyze the available information on nuclear-fusion cross sections that are most important for solar energy generation neutrino production. provide best values low-energy cross-section factors and, wherever possible, estimates of uncertainties. also describe experiments calculations required in order to improve our knowledge fusion rates.DOI:https://doi.org/10.1103/RevModPhys.70.1265©1998 American Physical Society
We present new improved constraints on the Hubble parameter H ( z ) in redshift range 0.15 < 1.1, obtained from differential spectroscopic evolution of early-type galaxies as a function redshift. extract large sample ∼ 11000) several surveys, spanning almost 8 billion years cosmic lookback time (0.15 1.42). select most massive, red elliptical galaxies, passively evolving and without signature ongoing star formation. Those can be used standard chronometers, firstly proposed by Jimenez...
The angular power spectrum of the cosmic microwave background (CMB) contains information on virtually all cosmological parameters interest, including geometry Universe ($\ensuremath{\Omega}$), baryon density, Hubble constant ($h$), ($\ensuremath{\Lambda}$), number light neutrinos, ionization history, and amplitudes spectral indices primordial scalar tensor perturbation spectra. We review imprint each parameter CMB. Assuming only that perturbations were adiabatic, we use a covariance-matrix...
Interest in the idea that primordial black holes (PBHs) might comprise some or all of dark matter has recently been rekindled following LIGO's first direct detection a binary-black-hole merger. Here we revisit effect accreting PBHs on cosmic microwave background (CMB) frequency spectrum and angular temperature/polarization power spectra. We compute accretion rate luminosity PBHs, accounting for their suppression by Compton drag cooling CMB photons. estimate gas temperature near Schwarzschild...
We consider particle decays during the cosmic dark ages with two aims: (1) to explain high optical depth reported by Wilkinson Microwave Anisotropy Probe (WMAP), and (2) provide new constraints parameter space for decaying particles. delineate decay channels in which most of energy ionizes heats intergalactic medium gas [and thus affects microwave background (CMB)], those is carried away---e.g. photons energies $100\mathrm{keV}\ensuremath{\lesssim}E\ensuremath{\lesssim}1\mathrm{TeV}$---and...
We explore the feasibility and astrophysical consequences of a new long-range $U(1)$ gauge field (``dark electromagnetism'') that couples only to dark matter, not standard model. The matter consists an equal number positive negative charges under force, but annihilations are suppressed if dark-matter mass is sufficiently high fine-structure constant $\stackrel{^}{\ensuremath{\alpha}}$ small. correct relic abundance can be obtained also conventional weak interactions, we verify this...
Primordial black holes (PBHs) have long been a candidate for the elusive dark matter (DM), and remain poorly constrained in $\ensuremath{\sim}20--100\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ mass range. PBH binaries were recently suggested as possible source of LIGO's first detections. In this paper, we thoroughly revisit existing estimates merger rate binaries. We compute probability distribution orbital parameters formed early Universe, accounting tidal torquing by all other PBHs, well...
The discovery that the cosmic expansion is accelerating has been followed by an intense theoretical and experimental response in physics astronomy. implies our most basic notions about how gravity work are violated on cosmological distance scales. One simple fix introduction of a constant into field equations for general relativity. However, extremely small value constant, relative to expectations, led theorists explore wide variety alternative explanations involve exotic negative-pressure...
Precise measurements of the cosmic microwave background (CMB) power spectrum are in excellent agreement with predictions standard $\Lambda$CDM cosmological model. However, there is some tension between value Hubble parameter $H_0$ inferred from CMB and that observations Universe at lower redshifts, unusually small dark-energy density a puzzling ingredient In this paper, we explore scenario new exotic energy behaves like constant early times then decays quickly critical redshift $z_c$. An...
We derive constraints on elastic scattering between baryons and dark matter using the cosmic microwave background (CMB) data from Planck satellite Lyman-alpha forest Sloan Digital Sky Survey. Elastic allows to exchange momentum, affecting dynamics of linear density perturbations in early Universe. cross sections form sigma \propto v^n, allowing for a wide range velocity dependencies with n -4 2. improve correct previous estimates where they exist, including velocity-independent section as...