18 research outputs found
Deciphering the Kaleidoscopic Universe with Multimessenger Physics
Cosmology is entering a new era as the number and precision of probes perpetually increase. Long-standing probes, such as the cosmic microwave background (CMB) and galaxy surveys, are cultivating high-precision tests for a wide array of cosmological models. Gravitational waves (GW), line-intensity mapping (IM), and other more recent probes are beginning to yield intricate astrophysical information about the creation of their distinct signals. In the upcoming decade, potential probes, such as active galactic nuclei (AGN) and neutrinos, will see favorable improvements in their characterizations. My research interests span across the various theoretical analyses of these types of probes, as each reveals a unique and complementary slice of information about the Universe. These slices, together, further complete a picture of the entire Universe, as well as cross-check the conclusions drawn from any single probe. Thus far, I have tested astrophysical and inflationary signatures with CMB secondaries; constrained dark matter and the anomalous EDGES signal with IM; characterized AGN variability with time-domain astronomy; and investigated the nature of astrophysical neutrinos with optical and neutrino telescopes
Chern-Simons Gravity and Neutrino Self-Interactions
Dynamical Chern-Simons gravity (dCS) is a four-dimensional parity-violating
extension of general relativity. Current models predict the effect of this
extension to be negligible due to large decay constants close to the scale
of grand unified theories. Here, we present a construction of dCS allowing for
much smaller decay constants, ranging from sub-eV to Planck scales.
Specifically, we show that if there exists a fermion species with strong
self-interactions, the short-wavelength fermion modes form a bound state. This
bound state can then undergo dynamical symmetry breaking and the resulting
pseudoscalar develops Yukawa interactions with the remaining long-wavelength
fermion modes. Due to this new interaction, loop corrections with gravitons
then realize a linear coupling between the pseudoscalar and the gravitational
Chern-Simons term. The strength of this coupling is set by the Yukawa coupling
constant divided by the fermion mass. Therefore, since self-interacting
fermions with small masses are ideal, we identify neutrinos as promising
candidates. For example, if a neutrino has a mass
and the Yukawa coupling is order unity, the dCS decay constant can be as small
as . We discuss other potential choices
for fermions.Comment: 9 pages 3 figure
Cross-correlation between thermal Sunyaev-Zeldovich effect and the integrated Sachs-Wolfe effect
Large-angle fluctuations in the cosmic microwave background temperature
induced by the integrated Sachs-Wolfe effect and Compton-y distortions from the
thermal Sunyaev-Zeldovich (tSZ) effect are both due to line-of-sight density
perturbations. Here we calculate the cross-correlation between these two
signals. Measurement of this cross-correlation can be used to test the redshift
distribution of the tSZ distortion, which has implications for the redshift at
which astrophysical processes in clusters begin to operate. We also evaluate
the detectability of a yT cross-correlation from exotic early-Universe sources
in the presence of this late-time effect.Comment: 5 pages, 3 figures, published in PR
Seeking Neutrino Emission from AGN through Temporal and Spatial Cross Correlation
Active galactic nuclei (AGN) are a promising source for high-energy
astrophysical neutrinos (HEANs). By the end of 2022, the Vera C. Rubin
Observatory (VRO) will begin to observe million AGN with a regular
and high cadence. Here, we evaluate the capacity of VRO, in tandem with various
current and upcoming neutrino telescopes, to establish AGN as HEAN emitters. To
do so, we assume that the neutrino luminosity from any given AGN at any given
time is proportional to the electromagnetic luminosity. We then estimate the
error with which this fraction can be measured through spatial and temporal
cross-correlation of VRO light curves with IceCube, KM3NeT, and Bakail-GVD. We
find that it may be possible to detect AGN contributions at the
level to the HEAN flux even if these AGN contribute only of the HEAN
flux. The bulk of this information comes from spatial correlations, although
the temporal information improves the sensitivity a bit. The results also imply
that if an angular correlation is detected with high signal-to-noise, there may
be prospects to detect a correlation between AGN variability and neutrino
arrival times. The small HEAN fraction estimated here to be accessible to the
entirety of the VRO AGN sample suggests that valuable information on the
character of the emitting AGN may be obtained through similar analyses on
different sub-populations of AGN.Comment: 8 pages, 6 figure
Magnetic Fields from Compensated Isocurvature Perturbations
Compensated isocurvature perturbations (CIPs) are perturbations to the
primordial baryon density that are accompanied by dark-matter-density
perturbations so that the total matter density is unperturbed. Such CIPs, which
may arise in some multi-field inflationary models, can be long-lived and only
weakly constrained by current cosmological measurements. Here we show that the
CIP-induced modulation of the electron number density interacts with the
electron-temperature fluctuation associated with primordial adiabatic
perturbations to produce, via the Biermann-battery mechanism, a magnetic field
in the post-recombinaton Universe. Assuming the CIP amplitude saturates the
current BBN bounds, this magnetic field can be stronger than
at and stronger by an order of magnitude
than that (produced at second order in the adiabatic-perturbation amplitude) in
the standard cosmological model, and thus can serve as a possible seed for
galactic dynamos.Comment: 7 pages, 2 figures, version accepted for publication in PR
Subtracting Compact Binary Foregrounds to Search for Subdominant Gravitational-Wave Backgrounds in Next-Generation Ground-Based Observatories
Stochastic gravitational-wave backgrounds (SGWBs) derive from the
superposition of numerous individually unresolved gravitational-wave (GW)
signals. Detecting SGWBs provides us with invaluable information about
astrophysics, cosmology, and fundamental physics. In this paper, we study SGWBs
from binary black-hole (BBH) and binary neutron-star (BNS) coalescences in a
network of next-generation ground-based GW observatories (Cosmic Explorer and
Einstein Telescope) and determine how well they can be measured; this then
limits how well we can observe other subdominant astrophysical and cosmological
SGWBs. We simulate all-Universe populations of BBHs and BNSs and calculate the
corresponding SGWBs, which consist of a superposition of (i) undetected
signals, and (ii) the residual background from imperfect removal of resolved
sources. The sum of the two components sets the sensitivity for observing other
SGWBs. Our results show that, even with next-generation observatories, the
residual background is large and limits the sensitivity to other SGWBs. The
main contributions to the residual background arise from uncertainties in
inferring the coalescence phase and luminosity distance of the detected
signals. Alternative approaches to signal subtraction would need to be explored
to minimize the BBH and BNS foreground in order to observe SGWBs from other
subdominant astrophysical and cosmological sources.Comment: 19 pages, 10 figures, matches the published versio
High-Energy Astrophysical Neutrinos from Cosmic Strings
Cosmic strings that couple to neutrinos may account for a portion of the
high-energy astrophysical neutrino (HEAN) flux seen by IceCube. Here, we
calculate the observed spectrum of neutrinos emitted from a population of
cosmic string loops that contain quasi-cusps, -kinks, or kink-kink collisions.
We consider two broad neutrino emission models: one where these string features
emit a neutrino directly, and one where they emit a scalar particle which then
eventually decays to a neutrino. In either case, the spectrum of cosmic string
neutrinos does not match that of the observed HEAN spectrum. We thus find that
the maximum contribution of cosmic string neutrinos, through these two
scenarios, to be at most % of the observed flux. However, we also
find that the presence of cosmic string neutrinos can lead to bumps in the
observed neutrino spectrum. Finally, for each of the models presented, we
present the viable parameter space for neutrino emission.Comment: 11 pages, 7 figure