arXiv subjects

Katelin Schutz

Publications and source records attributed to Katelin Schutz.

At least 37 records · Page 2Linked to original sources

arXiv2022

An Effective Bias Expansion for 21 cm Cosmology in Redshift Space

A near-future detection of the 21cm signal from the epoch of reionization will provide unique opportunities to probe the underlying cosmology, provided that such cosmological information can be extracted with precision. To this end, we further develop effective field theory (EFT) inspired techniques for the 21cm brightness temperature field during the epoch of reionization, incorporating renormalized bias and a treatment of redshift space distortions. Notably, we confirm that in redshift space, measures of the 21cm brightness, e.g the power spectrum, should have irreducible contributions that lack a bias coefficient and therefore contain direct, astrophysics-free information about the cosmological density field; in this work, we study this effect beyond linear order. To validate our theoretical treatment, we fit the predicted EFT Fourier-space shapes to the THESAN suite of hydrodynamical simulations of reionization at the field level, where the considerable number of modes prevents overfitting. We find agreement at the level of a few percent between the 21cm power spectrum from the EFT fits and simulations over the wavenumber range $k \lesssim 0.8$ h/Mpc and neutral fraction $x_\mathrm{HI} \gtrsim 0.4$, which is imminently measurable by the Hydrogen Epoch of Reionization Array (HERA) and future experiments. The ability of the EFT to describe the 21cm signal extends to simulations that have different astrophysical prescriptions for reionization as well as simulations with interacting dark matter.

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arXiv2022

A Predictive Mirror Twin Higgs with Small $\mathbf{Z}_2$ Breaking

The twin Higgs mechanism is a solution to the little hierarchy problem in which the top partner is neutral under the Standard Model (SM) gauge group. The simplest mirror twin Higgs (MTH) model -- where a $\mathbf{Z}_2$ symmetry copies each SM particle -- has too many relativistic degrees of freedom to be consistent with cosmological observations. We demonstrate that MTH models can have an observationally viable cosmology if the twin mass spectrum leads to twin neutrino decoupling before the SM and twin QCD phase transitions. Our solution requires the twin photon to have a mass of $\sim 20$ MeV and kinetically mix with the SM photon to mediate entropy transfer from the twin sector to the SM. This twin photon can be robustly discovered or excluded by future experiments. Additionally, the residual twin degrees of freedom present in the early Universe in this scenario would be detectable by future observations of the cosmic microwave background.

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arXiv2022

Early-Universe Model Building

Theoretical investigations into the evolution of the early universe are an essential part of particle physics that allow us to identify viable extensions to the Standard Model as well as motivated parameter space that can be probed by various experiments and observations. In this white paper, we review particle physics models of the early universe. First, we outline various models that explain two essential ingredients of the early universe (dark matter and baryon asymmetry) and those that seek to address current observational anomalies. We then discuss dynamics of the early universe in models of neutrino masses, axions, and several solutions to the electroweak hierarchy problem. Finally, we review solutions to naturalness problems of the Standard Model that employ cosmological dynamics.

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arXiv2022

Axion dark matter-induced echo of supernova remnants

Axions are a theoretically promising dark matter (DM) candidate. In the presence of radiation from bright astrophysical sources at radio frequencies, nonrelativistic DM axions can undergo stimulated decay to two nearly back-to-back photons, meaning that bright sources of radio waves will have a counterimage ("gegenschein") in nearly the exact opposite spatial direction. The counterimage will be spectrally distinct from backgrounds, taking the form of a narrow radio line centered at $ν= m_a/4π$ with a width determined by Doppler broadening in the DM halo, $Δν/ν\sim 10^{-3}$. In this work, we show that the axion decay-induced echoes of supernova remnants may be bright enough to be detectable. Their non-detection may be able to set the strongest limits to date on axion DM in the $\sim 1-10 \, μ$eV mass range where there are gaps in coverage from existing experiments.

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arXiv2022

The Physics of Light Relics

Many well-motivated extensions of the Standard Model predict the existence of new light species that may have been produced in the early universe. Prominent examples include axions, sterile neutrinos, gravitinos, dark photons, and more. The gravitational influence of light relics leaves imprints in the cosmic microwave background fluctuations, the large-scale structure of the universe and the primordial element abundances. In this paper, we detail the physics of cosmological light relics, and describe how measurements of their relic density and mass serve as probes of physics beyond the Standard Model. A measurement of the light relic density at the precision of upcoming cosmological surveys will point the way toward new physics or severely constrain the range of viable extensions to the Standard Model.

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arXiv2022

Dark Matter Physics from the CMB-S4 Experiment

The nature of dark matter is one of the major puzzles of fundamental physics, integral to the understanding of our universe across almost every epoch. The search for dark matter takes place at different energy scales, and use data ranging from particle colliders to astrophysical surveys. We focus here on CMB-S4, a future ground-based Cosmic Microwave Background (CMB) experiment, which is expected to provide exquisite measurements of the CMB temperature and polarization anisotropies. These measurements (on their own and in combination with other surveys) will allow for new means to shed light on the nature of dark matter.

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arXiv2021

A Helioscope for Gravitationally Bound Millicharged Particles

Particles may be emitted efficiently from the solar interior if they are sufficiently light and weakly coupled to the solar plasma. In a narrow region of phase space, they are emitted with velocities smaller than the escape velocity of the solar system, thereby populating a gravitationally bound density that can accumulate over the solar lifetime, referred to as a "solar basin." Detection strategies that can succeed in spite of (or even be enhanced by) the low particle velocities are therefore poised to explore new regions of parameter space when taking this solar population into account. Here we identify "direct deflection" as a powerful method to detect such a population of millicharged particles. This approach involves distorting the local flow of gravitationally bound millicharges with an oscillating electromagnetic field and measuring these distortions with a resonant LC circuit. Since it is easier to distort the flow of slowly moving particles, the signal is parametrically enhanced by the small solar escape velocity near Earth. The proposed setup can probe couplings an order of magnitude smaller than other methods for millicharge masses ranging from 100 meV to 100 eV and can operate concurrently as a search for sub-GeV millicharged dark matter. The signal power scales as the millicharge coupling to the eighth power, meaning that even with conservative assumptions, direct deflection could begin to explore new regions of parameter space. We also highlight novel features of millicharge solar basins, including those associated with the phase space distribution and the possibility for the occupation number to vastly exceed that of a thermal distribution.

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arXiv2021

The Galactic potential and dark matter density from angular stellar accelerations

We present an approach to measure the Milky Way (MW) potential using the angular accelerations of stars in aggregate as measured by astrometric surveys like Gaia. Accelerations directly probe the gradient of the MW potential, as opposed to indirect methods using e.g. stellar velocities. We show that end-of-mission Gaia stellar acceleration data may be used to measure the potential of the MW disk at approximately 3$σ$ significance and, if recent measurements of the solar acceleration are included, the local dark matter density at ~2$σ$ significance. Since the significance of detection scales steeply as $t^{5/2}$ for observing time $t$, future surveys that include angular accelerations in the astrometric solutions may be combined with Gaia to precisely measure the local dark matter density and shape of the density profile.

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arXiv2020

The cosmology of sub-MeV dark matter freeze-in

Dark matter (DM) could be a relic of freeze-in through a light mediator, where the DM is produced by extremely feeble, IR-dominated processes in the thermal Standard Model plasma. In the simplest viable models with the DM mass below the MeV scale, the DM has a small effective electric charge and is born with a nonthermal phase-space distribution. This DM candidate would cause observable departures from standard cosmological evolution. In this work, we combine data from the cosmic microwave background (CMB), Lyman-$α$ forest, quasar lensing, stellar streams, and Milky Way satellite abundances to set a lower limit on freeze-in DM masses up to $\sim 20\,$keV, with the exact constraint depending on whether the DM thermalizes in its own sector. We perform forecasts for the CMB-S4 experiment, the Hydrogen Epoch of Reionization Array, and the Vera Rubin Observatory, finding that freeze-in DM masses up to $\sim 80\,$keV can be explored. These cosmological probes are highly complementary with proposed direct-detection efforts to search for this DM candidate.

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arXiv2020

The Subhalo Mass Function and Ultralight Bosonic Dark Matter

Warm dark matter has recently become increasingly constrained by observational inferences about the low-mass end of the subhalo mass function, which would be suppressed by dark matter free streaming in the early Universe. In this work, we point out that a constraint can be placed on ultralight bosonic dark matter (often referred to as "fuzzy dark matter") based on similar considerations. Recent limits on warm dark matter from strong gravitational lensing of quasars and from fluctuations in stellar streams separately translate to a lower limit of $\sim 2.1 \times 10^{-21}$ eV on the mass of an ultralight boson comprising all dark matter. These limits are complementary to constraints on ultralight dark matter from the Lyman-$α$ forest and are subject to a completely different set of assumptions and systematic uncertainties. Taken together, these probes strongly suggest that dark matter with a mass $\sim 10^{-22}$ eV is not a viable way to reconcile differences between cold dark matter simulations and observations of structure on small scales.

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arXiv2019

Gravitational wave probes of dark matter: challenges and opportunities

In this white paper, we discuss the prospects for characterizing and identifying dark matter using gravitational waves, covering a wide range of dark matter candidate types and signals. We argue that present and upcoming gravitational wave probes offer unprecedented opportunities for unraveling the nature of dark matter and we identify the most urgent challenges and open problems with the aim of encouraging a strong community effort at the interface between these two exciting fields of research.

astro-ph.CO↗

arXiv2019

Evaporating the Milky Way halo and its satellites with inelastic self-interacting dark matter

Self-interacting dark matter provides a promising alternative for the cold dark matter paradigm to solve potential small-scale galaxy formation problems. Nearly all self-interacting dark matter simulations so far have considered only elastic collisions. Here we present simulations of a galactic halo within a generic inelastic model using a novel numerical implementation in the Arepo code to study arbitrary multi-state inelastic dark matter scenarios. For this model we find that inelastic self-interactions can: (i) create larger subhalo density cores compared to elastic models for the same cross section normalisation; (ii) lower the abundance of satellites without the need for a power spectrum cutoff; (iii) reduce the total halo mass by about 10%; (iv) inject the energy equivalent of O(100) million Type II supernovae in galactic haloes through level de-excitation; (v) avoid the gravothermal catastrophe due to removal of particles from halo centers. We conclude that a ~5 times larger elastic cross section is required to achieve the same central density reduction as the inelastic model. This implies that well-established constraints on self-interacting cross sections have to be revised if inelastic collisions are the dominant mode. In this case significantly smaller cross sections can achieve the same core density reduction thereby increasing the parameter space of allowed models considerably.

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arXiv2019

Cosmological Probes of Dark Matter Interactions: The Next Decade

Cosmological observations offer unique and robust avenues for probing the fundamental nature of dark matter particles-they broadly test a range of compelling theoretical scenarios, often surpassing or complementing the reach of terrestrial and other experiments. We discuss observational and theoretical advancements that will play a pivotal role in realizing a strong program of cosmological searches for the identity of dark matter in the coming decade. Specifically, we focus on measurements of the cosmic-microwave-background anisotropy and spectral distortions, and tracers of structure (such as the Lyman-$α$ forest, galaxies, and the cosmological 21-cm signal).

astro-ph.CO↗

arXiv2019

Making dark matter out of light: freeze-in from plasma effects

Dark matter (DM) could couple to particles in the Standard Model (SM) through a light vector mediator. In the limit of small coupling, this portal could be responsible for producing the observed DM abundance through a mechanism known as freeze-in. Furthermore, the requisite DM-SM couplings provide a concrete benchmark for direct and indirect searches for DM. In this paper, we present updated calculations of the relic abundance for DM produced by freeze-in through a light vector mediator. We identify an additional production channel: the decay of photons that acquire an in-medium plasma mass. These plasmon decays are a dominant channel for DM production for sub-MeV DM masses, and including this channel leads to a significant reduction in the predicted signal strength for DM searches. Accounting for production from both plasmon decays and annihilations of SM fermions, the DM acquires a highly non-thermal phase space distribution which impacts the cosmology at later times; these cosmological effects will be explored in a companion paper.

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arXiv2019

SIMPs through the axion portal

Dark matter could be a thermal relic comprised of strongly interacting massive particles (SIMPs), where $3 \rightarrow 2$ interactions set the relic abundance. Such interactions generically arise in theories of chiral symmetry breaking via the Wess-Zumino-Witten term. In this work, we show that an axion-like particle can successfully maintain kinetic equilibrium between the dark matter and the visible sector, allowing the requisite entropy transfer that is crucial for SIMPs to be a cold dark matter candidate. Constraints on this scenario arise from beam dump and collider experiments, from the cosmic microwave background, and from supernovae. We find a viable parameter space when the axion-like particle is close in mass to the SIMP dark matter, with strong-scale masses of order a few hundred MeV. Many planned experiments are set to probe the parameter space in the near future.

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arXiv2018

Constraining a Thin Dark Matter Disk with Gaia

If a component of the dark matter has dissipative interactions, it could collapse to form a thin dark disk in our Galaxy that is coplanar with the baryonic disk. It has been suggested that dark disks could explain a variety of observed phenomena, including periodic comet impacts. Using the first data release from the $Gaia$ space observatory, we search for a dark disk via its effect on stellar kinematics in the Milky Way. Our new limits disfavor the presence of a thin dark matter disk, and we present updated measurements on the total matter density in the Solar neighborhood.

astro-ph.GA↗

arXiv2017

Pulsar timing can constrain primordial black holes in the LIGO mass window

The recent discovery of gravitational waves from merging black holes has generated interest in primordial black holes as a possible component of the dark matter. In this paper, we show that pulsar timing may soon have sufficient data to constrain $1$-$1000\,M_{\odot}$ primordial black holes via the non-detection of a third-order Shapiro time delay as the black holes move around the Galactic halo. We present the results of a Monte Carlo simulation which suggests that future data from known pulsars may be capable of constraining the PBH density more stringently than other existing methods in the mass range ~1-30$\,M_{\odot}$. We find that timing new pulsars discovered using the proposed Square Kilometre Array may constrain primordial black holes in this mass range to comprise less than ~1-10% of the dark matter.

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arXiv2016

On the Detectability of Light Dark Matter with Superfluid Helium

We show that a two-excitation process in superfluid helium, combined with sensitivity to meV energy depositions, can probe dark matter down to the ~keV warm dark matter mass limit. This mass reach is three orders of magnitude below what can be probed with ordinary nuclear recoils in helium at the same energy resolution. For dark matter lighter than $\sim 100$ keV, the kinematics of the process requires the two athermal excitations to have nearly equal and opposite momentum, potentially providing a built-in coincidence mechanism for controlling backgrounds.

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