Talks & Events
KICP Friday Noon Seminars
Current & Future KICP Seminars
Past KICP Seminars
Coherent neutrino-nucleus scattering: signal or background?
The next generation of dark matter direct detection experiments will be sensitive to coherent nuclear scattering of solar neutrinos. This presents an irreducible background to dark matter searches, the so called 'neutrino floor'. However, this effect that has yet to be observed and so provides an opportunity for discovery. Dedicated experiments are racing to observe this effect and use it as a probe of new physics. In this talk I will discuss the neutrino floor and present some dark matter models where the prospects for discovery are not so grim. Then I will introduce the MINER experiment, a Texas A&M effort to observe coherent neutrino-nucleus scattering, and present its sensitivity to models of new physics.
From axion inflation to leptons, baryons and cosmological magnetic fields
Axions are attractive candidates for theories of large-field inflation that are capable of generating observable primordial gravitational wave backgrounds. These fields enjoy shift-symmetries that protect their role as inflatons from being spoiled by coupling to unknown UV physics. This symmetry also restricts the couplings of these axion fields to other matter fields. At lowest order, the only allowed interactions are derivative couplings to gauge fields and fermions. These derivative couplings lead to the biased production of fermion and gauge-boson helicity states during and after inflation. I will describe some recent work on preheating in axion-inflation models that are derivatively coupled to Abelian gauge-fields and fermion axial-currents.
For an axion coupled to U(1) gauge fields it was found that preheating is efficient for a wide range of parameters. In certain cases the inflaton is seen to transfer all its energy to the gauge fields within a few oscillations. Identifying the gauge field as the hypercharge sector of the Standard Model can lead to the generation of cosmologically relevant magnetic fields.
Coupling the inflaton-axion to Majorana fermions leads to the biased production of fermion helicity-states which can have interesting phenomenological implications for leptogenesis.
Recent Advances & Current Challenges in Cosmology with Galaxy Clusters
Observations of galaxy clusters not only test the basic parameters of the Lambda-CDM universe, but also test new physics such as non-zero neutrino masses, evolving dark energy, and departures from General Relativity on large scales. In this talk, I will first motivate why clusters are so useful for cosmology and why we are confident that these measurements are robust. In particular, I will describe how gravitational lensing measurements have been essential to cosmological constraints with the Weighing the Giants project, which reported a 12% constraint on Omega_m and a 15% constraint on a constant dark energy equation of state (when assuming flatness) from cluster data alone. While currently competitive, control of systematic uncertainties in weak lensing measurements need to improve by an order of magnitude to fully realize the potential of cluster cosmology with Stage-IV dark energy experiments that are turning on in the coming decade. I will detail some of the ongoing work within the South Pole Telescope and Dark Energy Science collaborations that is moving us towards the 1% systematics level, and highlight some of the interesting challenges yet to be solved.
Testing neutrino properties with cosmological observables
One of the great puzzles related to the ΛCDM model is the nature of the dark matter (DM) component. In standard cosmology, hot, thermal relics are identified with the three light, active neutrinos which are sub-eV elementary particles which, apart from gravity, only interact via weak interactions. From neutrino oscillation experiments we know that neutrinos have masses but they are not sensitive to the absolute neutrino mass scale. Cosmology provides an independent tool to tackle the absolute scale of neutrino and to study its properties. In this talk I will illustrate the implications of neutrino properties on cosmological observables, in particular on the Cosmic Microwave Background radiation and on Large Scale Structure, and I will explore the current constraints on neutrino masses focusing also on the dependence of the cosmological limits on the total neutrino mass under the assumption of different mass spectra.
Cosmological Gravitational Waves: Causal Structure And Memories
Despite being associated with particles of zero rest mass, electromagnetic and gravitational waves do not travel solely on the null cone in generic curved spacetimes. (That is, light does not always propagate on the light cone.) This inside-the-null-cone propagation of waves is known as the tail effect, and finding novel ways of understanding it in the strong field regime near a black hole may find applications for modeling the gravitational signals sought after by next-generation space-based detectors such as LISA.
Motivated by these considerations -- and as a first step -- I have been exploring techniques to understand the causal structure of scalar, electromagnetic and gravitational waves in cosmological spacetimes. I will describe my efforts to date, which include how the gravitational wave memory effects in 4D asymptotically flat spacetime generalize to the cosmological case.
Standard Model Background of the Cosmological Collider
Primordial non-Gaussianities record interactions of fields in the early universe, which can be viewed as collision events in a "Cosmological Collider" with huge energy. In this talk, I shall introduce the workings of the Cosmological Collider as an explorer of new physics at very high scales, and describe the Standard Model spectrum during inflation and its "background signals" in Cosmological Collider. The nontrivial quantum correction during inflation plays a crucial role in this process, which I shall describe in detail.
Simulating Milky Way-like Galaxies with Realistic Satellite Populations
Low-mass 'dwarf' galaxies trace structure formation on the smallest cosmological scales and represent the most significant challenges to the cold dark matter (CDM) model. I will introduce the Latte simulations, a new suite of cosmological zoom-in baryonic simulations that model the formation of Milky Way-like galaxies at parsec-scale resolution, using the FIRE (Feedback in Realistic Environments) model for star formation and feedback. Using these simulations, I will discuss the roles of cosmic accretion and stellar feedback in driving the formation and structure of disk galaxies like the Milky Way. These simulations also self-consistently resolve the satellite dwarf galaxies that form around each host. I will discuss the impact of stellar feedback and MW-like environments on dark-matter subhalos and their connection to dwarf galaxies, demonstrating progress in addressing the 'missing satellites' and 'too-big-to-fail' problems of LCDM cosmology.
Precision searches for new physics using optically levitated microspheres
I will describe the development of a new class of force sensors based on optically levitated dielectric microspheres in high vacuum, which allow the detection of sub-attonewton forces acting on micron sized objects. These force sensors can enable novel precision searches for new physics through the detection of weakly coupled or short range (<< 1 mm) interactions. Results from the initial application of these force sensors to search for millicharged dark matter particles bound in matter, and for interactions arising in certain screened scalar dark energy models, will be presented. Finally, I will discuss the expected sensitivity of these techniques to search for non-Newtonian or non-Coulombic forces at micron length scales, which can probe a variety of models of physics beyond the Standard Model.
Kinetic Inductance Detectors for 100 GHz CMB Polarimetry
Kinetic inductance detectors (KIDs) are a promising detector technology across a broad range of wavelengths from mm-waves up to the soft X-ray regime. KIDs offer relatively simple, relatively inexpensive fabrication and straightforward passive frequency-domain multiplexing, which makes them an attractive solution for instruments requiring very high pixel-count arrays, including upcoming CMB polarimetry instruments. In this talk, I will describe a recent effort to produce a prototype array of direct-absorbing lumped element KIDs designed for CMB polarimetry at 100 GHz (3 mm) with the QUBIC telescope, including a discussion of design considerations, material development, and measured array performance.
Delensing CMB B-modes: results from SPT
A promising signature of cosmic inflation is the presence of a "B-mode" component in the polarization of the Cosmic Microwave Background (CMB) induced by primordial gravitational waves. For many inflation models, this B-mode signal is predicted to be at a level detectable in the near future. However current searches are limited by a "lensing B-mode" component that is produced by gravitationally lensing primordial E modes. In order to potentially detect the inflationary signal from B-mode measurements, lensing B modes must be characterized and removed in a process referred to as "delensing." This process has been studied extensively theoretically and with simulations, but has not been performed on polarization data. In this talk, I will present a demonstration of CMB B-mode delensing using polarization data from the South Pole Telescope polarimeter, SPTpol. Furthermore, using realistic simulations that include filtering and realistic CMB noise, we will show what is currently limiting the delensing efficiency and how it will rapidly improve in the near future.