79 research outputs found
CosMIn: The Solution to the Cosmological Constant Problem
The current acceleration of the universe can be modeled in terms of a
cosmological constant. We show that the extremely small value of \Lambda L_P^2
~ 3.4 x 10^{-122}, the holy grail of theoretical physics, can be understood in
terms of a new, dimensionless, conserved number CosMIn (N), which counts the
number of modes crossing the Hubble radius during the three phases of evolution
of the universe. Theoretical considerations suggest that N ~ 4\pi. This single
postulate leads us to the correct, observed numerical value of the cosmological
constant! This approach also provides a unified picture of cosmic evolution
relating the early inflationary phase to the late-time accelerating phase.Comment: ver 2 (6 pages, 2 figures) received Honorable Mention in the Gravity
Research Foundation Essay Contest, 2013; to appear in Int.Jour.Mod.Phys.
Cosmic Information, the Cosmological Constant and the Amplitude of primordial perturbations
A unique feature of gravity is its ability to control the information
accessible to any specific observer. We quantify the notion of cosmic
information ('CosmIn') for an eternal observer in the universe. Demanding the
finiteness of CosmIn requires the universe to have a late-time accelerated
expansion. Combining the introduction of CosmIn with generic features of the
quantum structure of spacetime (e.g., the holographic principle), we present a
holistic model for cosmology. We show that (i) the numerical value of the
cosmological constant, as well as (ii) the amplitude of the primordial, scale
invariant, perturbation spectrum can be determined in terms of a single free
parameter, which specifies the energy scale at which the universe makes a
transition from a pre-geometric phase to the classical phase. For a specific
value of the parameter, we obtain the correct results for both (i) and (ii).
This formalism also shows that the quantum gravitational information content of
spacetime can be tested using precision cosmology.Comment: 9 pages; 1 figur
Constraining the evolution of CII intensity through the end stages of reionization
We combine available constraints on the local CII 158 m line luminosity
function from galaxy observations (Hemmati et al. 2017), with the evolution of
the star-formation rate density and the recent CII intensity mapping
measurement in Pullen et al. (2018, assuming detection), to derive the
evolution of the CII luminosity - halo mass relation over . We
develop convenient fitting forms for the evolution of the CII luminosity - halo
mass relation, and forecast constraints on the CII intensity mapping power
spectrum and its associated uncertainty across redshifts. We predict the
sensitivities to detect the power spectrum for upcoming PIXIE-, STARFIRE-,
EXCLAIM-, CONCERTO-, TIME- and CCAT-p-like surveys, as well as possible future
intensity mapping observations with the ALMA facility.Comment: 10 pages, 9 figures, 2 tables; version accepted for publication in
MNRA
Constraining a halo model for cosmological neutral hydrogen
We describe a combined halo model to constrain the distribution of neutral
hydrogen (HI) in the post-reionization universe. We combine constraints from
the various probes of HI at different redshifts: the low-redshift 21-cm
emission line surveys, intensity mapping experiments at intermediate redshifts,
and the Damped Lyman-Alpha (DLA) observations at higher redshifts. We use a
Markov Chain Monte Carlo (MCMC) approach to combine the observations and place
constraints on the free parameters in the model. Our best-fit model involves a
relation between neutral hydrogen mass and halo mass with a
non-unit slope, and an upper and a lower cutoff. We find that the model fits
all the observables but leads to an underprediction of the bias parameter of
DLAs at . We also find indications of a possible tension between
the HI column density distribution and the mass function of HI-selected
galaxies at . We provide the central values of the parameters of the
best-fit model so derived. We also provide a fitting form for the derived
evolution of the concentration parameter of HI in dark matter haloes, and
discuss the implications for the redshift evolution of the HI-halo mass
relation.Comment: 10 pages, 9 figures, 2 tables; version accepted for publication in
MNRA
Synergizing 21 cm and sub-millimetre surveys during reionization: new empirical insights
We use the latest results from Atacama Large Millimetre/submillimetre Array
(ALMA) surveys targeting the ionized carbon [CII] 158 m and oxygen [OIII]
88 m lines, in combination with data-driven predictions for the evolution
of neutral hydrogen (HI), to illustrate the prospects for intensity mapping
cross-correlations between 21 cm and submillimetre surveys over .
We work with a dataset including the ALPINE and REBELS surveys for [CII] over
, and ALMA [OIII] detections over . The resultant
evolution of the [CII] luminosity - halo mass relation is well described by a
double power law at high redshifts, with the best-fitting parameters in good
agreement with the results of simulations. The data favour secure detections of
the auto-power spectrum of [CII] at all redshifts with an enhanced Fred Young
Submillimetre Telescope (FYST)-like configuration. Such an experiment, along
with the Murchinson Widefield Array (MWA) will be able to measure the 21 cm -
[CII] cross-correlation power with a signal-to-noise ratio of a few tens to a
few hundreds. We find that a balloon-borne experiment improving upon the
Experiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) should be
able to detect the 21 cm - [OIII] cross-correlation with the MWA and the Square
Kilometre Array (SKA)-LOW out to . Our results have implications for
constraining the evolution of luminous sources during the mid-to-end stages of
reionization.Comment: 13 pages, 7 figures, 3 tables; version accepted for publication in
MNRA
Cross-correlating 21 cm and galaxy surveys: implications for cosmology and astrophysics
We forecast astrophysical and cosmological parameter constraints from
synergies between 21 cm intensity mapping and wide field optical galaxy surveys
(both spectroscopic and photometric) over . We focus on the
following survey combinations in this work: (i) a CHIME-like and DESI-like
survey in the northern hemisphere, (ii) an LSST-like and SKA I MID-like survey
and (ii) a MeerKAT-like and DES-like survey in the southern hemisphere. We work
with the CDM cosmological model having parameters , parameters and representing the cutoff
and slope of the HI-halo mass relation in the previously developed HI halo
model framework, and a parameter that represents the scale dependence of
the optical galaxy bias. Using a Fisher forecasting framework, we explore (i)
the effects of the HI and galaxy astrophysical uncertainties on the
cosmological parameter constraints, assuming priors from the present knowledge
of the astrophysics, (ii) the improvements on astrophysical constraints over
their current priors in the three configurations considered, (ii) the
tightening of the constraints on the parameters relative to the corresponding
HI auto-correlation surveys alone.Comment: 9 pages, 5 figures, 2 tables; accepted for publication in MNRA
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