1,020 research outputs found
Thermal Friction as a Solution to the Hubble and Large-Scale Structure Tensions
Thermal friction offers a promising solution to the Hubble and the
large-scale structure (LSS) tensions. This additional friction acts on a scalar
field in the early universe and extracts its energy density into dark
radiation, the cumulative effect being similar to that of an early dark energy
(EDE) scenario. The dark radiation automatically redshifts at the minimal
necessary rate to improve the Hubble tension. On the other hand, the addition
of extra radiation to the Universe can improve the LSS tension. We explore this
model in light of cosmic microwave background (CMB), baryon acoustic
oscillation and supernova data, including the SH0ES measurement and the
Dark Energy Survey Y1 data release in our analysis. Our results indicate a
preference for the regime where the scalar field converts to dark radiation at
very high redshifts, asymptoting effectively to an extra self-interacting
radiation species rather than an EDE-like injection. In this limit, thermal
friction can ease both the Hubble and the LSS tensions, but not resolve them.
We find the source of this preference to be the incompatibility of the CMB data
with the linear density perturbations of the dark radiation when injected at
redshifts close to matter-radiation equality.Comment: 10 pages, 8 figures, 7 tables (+ 8 pages, 3 figures, 3 tables in
appendix
Minimal Thermal Friction in Cosmology
Many cosmological datasets contain information about the fundamental building blocks of nature and the forces that govern them. In my research I focus on the connection between particle physics and the evolution of our universe, looking for new physics beyond the Standard Model of particle physics, and beyond CDM, the concordance model of cosmology. The majority of this work explores how a minimal thermal friction mechanism, emerging from first principle particle dynamics, can improve cosmological model building.
In the context of cosmic inflation, I investigate in detail how coupling a rolling axion to a non-Abelian gauge group gives rise to thermal friction, which can alter theoretical predictions for observables in a manner that is consistent with all currently available data while making unique predictions for future data. In particular, the presence of the thermal friction and the resulting thermal bath during inflation suppresses the tensor-to-scalar ratio r, and produces unique non-gaussianities that may be observable within the next ten years in the regime in which thermal friction is dominant.
I also explore how this minimal thermal friction can address the Hubble tension. A new component added to CDM that behaves like a cosmological constant at early times and then dilutes away as radiation or faster can resolve the Hubble tension. Coupling a rolling axion to a non-Abelian gauge group gives rise to thermal friction which sources a thermal bath. I show that the coupled system of rolling axion and thermal bath automatically exhibits the characteristic behavior of the extra components that are able to resolve the Hubble tension at the background level. These characteristics make this model robust to a wide class of scalar field potentials, thus providing a promising candidate for a natural particle-physics model solution to the Hubble tension.
My work additionally considers long lived decaying massive relics as an explanation for the anomalous high energy neutrino flux detected at IceCube. I explore this UV-extension to the Standard model in detail, considering a variety of cosmological data sets, as well as incorporating electroweak corrections, which become important at high energies. For this project I implemented a Monte Carlo simulation, taking into account electroweak showering processes, as well as a cosmological propagation code, capturing modifications to neutrino energy distributions through re-scatterings
Minimal Warm Inflation
Slow-roll inflation is a successful paradigm. However we find that even a
small coupling of the inflaton to other light fields can dramatically alter the
dynamics and predictions of inflation. As an example, the inflaton can
generically have an axion-like coupling to gauge bosons. Even relatively small
couplings will automatically induce a thermal bath during inflation. The
thermal friction from this bath can easily be stronger than Hubble friction,
significantly altering the usual predictions of any particular inflaton
potential. Thermal effects suppress the tensor-to-scalar ratio
significantly, and predict unique non-gaussianities. This axion-like coupling
provides a minimal model of warm inflation which avoids the usual problem of
thermal backreaction on the inflaton potential. As a specific example, we find
that hybrid inflation with this axion-like coupling can easily fit the current
cosmological data.Comment: 18 pages, 1 figure, v2: We added additional references and clarifying
comments in the introduction. We added an estimate on thermalization in
section III, and an additional comment on cosine-like potentials in section
IV, and a footnote commenting on equation 12. v2 matches published versio
The Cosmology of Dark Energy Radiation
In this work, we quantify the cosmological signatures of dark energy
radiation -- a novel description of dark energy, which proposes that the
dynamical component of dark energy is comprised of a thermal bath of
relativistic particles sourced by thermal friction from a slowly rolling scalar
field. For a minimal model with particle production emerging from first
principles, we find that the abundance of radiation sourced by dark energy can
be as large as , exceeding the bounds on relic dark
radiation by three orders of magnitude. Although the background and
perturbative evolution of dark energy radiation is distinct from Quintessence,
we find that current and near-future cosmic microwave background and supernova
data will not distinguish these models of dark energy. We also find that our
constraints on all models are dominated by their impact on the expansion rate
of the Universe. Considering extensions that allow the dark radiation to
populate neutrinos, axions, and dark photons, we evaluate the direct detection
prospects of a thermal background comprised of these candidates consistent with
cosmological constraints on dark energy radiation. Our study indicates that a
resolution of is required to achieve sensitivity to
relativistic neutrinos compatible with dark energy radiation in a neutrino
capture experiment on tritium. We also find that dark matter axion experiments
lack sensitivity to a relativistic thermal axion background, even if enhanced
by dark energy radiation, and dedicated search strategies are required to probe
new parameter space. We derive constraints arising from a dark photon
background from oscillations into visible photons, and find that several orders
of magnitude of viable parameter space can be explored with planned
experimental programs such as DM Radio and LADERA.Comment: 27 pages, 16 figures, 3 table
Measurement of single charged pion production in the charged-current interactions of neutrinos in a 1.3 GeV wide band beam
Single charged pion production in charged-current muon neutrino interactions
with carbon is studied using data collected in the K2K long-baseline neutrino
experiment. The mean energy of the incident muon neutrinos is 1.3 GeV. The data
used in this analysis are mainly from a fully active scintillator detector,
SciBar. The cross section for single production in the resonance
region ( GeV/) relative to the charged-current quasi-elastic cross
section is found to be 0.734 . The energy-dependent cross
section ratio is also measured. The results are consistent with a previous
experiment and the prediction of our model.Comment: 15 pages, 12 figures, 7 tables. Uses revtex4. Minor revisions to
match version accepted for publication in Physical Review
Experimental study of the atmospheric neutrino backgrounds for proton decay to positron and neutral pion searches in water Cherenkov detectors
The atmospheric neutrino background for proton decay to positron and neutral
pion in ring imaging water Cherenkov detectors is studied with an artificial
accelerator neutrino beam for the first time. In total, about 314,000 neutrino
events corresponding to about 10 megaton-years of atmospheric neutrino
interactions were collected by a 1,000 ton water Cherenkov detector (KT). The
KT charged-current single neutral pion production data are well reproduced by
simulation programs of neutrino and secondary hadronic interactions used in the
Super-Kamiokande (SK) proton decay search. The obtained proton to positron and
neutral pion background rate by the KT data for SK from the atmospheric
neutrinos whose energies are below 3 GeV is about two per megaton-year. This
result is also relevant to possible future, megaton-scale water Cherenkov
detectors.Comment: 13 pages, 16 figure
Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC
The uncertainty on the calorimeter energy response to jets of particles is
derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the
calorimeter response to single isolated charged hadrons is measured and
compared to the Monte Carlo simulation using proton-proton collisions at
centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009
and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter
response to specific types of particles (positively and negatively charged
pions, protons, and anti-protons) is measured and compared to the Monte Carlo
predictions. Finally, the jet energy scale uncertainty is determined by
propagating the response uncertainty for single charged and neutral particles
to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3%
for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table,
submitted to European Physical Journal
Standalone vertex ďŹnding in the ATLAS muon spectrometer
A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at âs = 7 TeV collected with the ATLAS detector at the LHC during 2011
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