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Friday, January 26th 2018

12:30 pm:

The cosmological LambdaCDM standard model faces some problems related to the formation of structures at relatively small scales, most notably the missing-satellites problem, the cusp-core problem, the too-big-to-fail problem, and the diversity problem. I will advertise late kinetic decoupling of dark matter as a mechanism to address the missing satellites problem. Afterwards, I will describe a model involving self-interacting dark matter and sterile neutrinos that can tackle all four small-scale problems.

Friday, February 2nd 2018

12:30 pm:

Friday, February 9th 2018

12:30 pm:

Many theories of beyond Standard Model physics include new light, weakly-coupled particles, which can be challenging to search for experimentally. The high densities and temperatures in stellar cores allow them to produce such particles in large numbers, while the large volume to surface area ratio of stars enhances the relative effects of such production on stellar energy transfer and cooling. This makes stellar observations into a sensitive probe of new particles. I’ll describe how the plasma environment in stellar cores can parametrically alter the rates for these processes, and how this can significantly change the constraints and discovery potential for some new particle candidates. I’ll also discuss some other situations where in-medium effects are important in the search for weakly-coupled new physics.

Friday, February 16th 2018

12:30 pm:

Friday, February 23rd 2018

12:45 pm:

If the Peccei-Quinn symmetry breaking field is displaced from its minimum

during inflation, the axion isocurvature spectrum is generically strongly

blue tilted with a break transition to a flat spectrum. A test of this

scenario with the Planck and BOSS DR11 data will be presented. Encouraging

results and its implications for future probes of axions and inflationary

cosmology will be discussed.

Friday, March 2nd 2018

12:30 pm:

Semi-annihilation describes processes with an initial state of two dark matter particles, and a final state of one plus standard model states. It is a generic feature of dark matter whenever the symmetry group enforcing stability is not a discrete Z2. Semi-annihilation changes the expected signals in current dark matter searches. With the bounds on standard thermal dark matter becoming very strong, now is the ideal time to ask to what extent those bounds apply to semi-annihilation, and what interesting parameter space remains. In this talk, explore the parameter space in a generic, bottom-up approach. We discuss the subtleties involved with semi-annihilation of fermionic dark matter, the role of additional unstable dark sector particles, and the interplay of semi-annihilation and the non-perturbative Sommerfeld effect. We discuss how semi-annihilation may relate to various anomalies seen in cosmic ray searches. Finally, we use an effective field theory approach to place limits in as model-independent a fashion as possible. We find that current searches are effective for processes with coloured final states, but significant model space for semi-annihilation still remains.

Friday, March 9th 2018

12:30 pm:

The little hierarchy problem of supersymmetry has to do with the question of why the electroweak breaking scale is small compared to the increasingly stringent lower limits on superpartner masses from the LHC. I discuss the possibility of addressing this problem by using hidden sector superconformal renormalization effects. This drives the soft supersymmetry breaking scalar squared mass terms in the Minimal Supersymmetric Standard Model towards quasi-fixed points in the infrared. I discuss the features of such models, and the extent to which the quasi-fixed point effects may ameliorate the little hierarchy problem.

Friday, March 16th 2018

12:30 pm:

Friday, March 23rd 2018

12:30 pm:

I will explore the generalization of the Feynman path integral in quantum field theory to complexified fields, and explain how it can be utilized to tackle the famous "sign problem". The sign problem prevents first principle studies of real-time dynamics and finite density systems via lattice field theory and appears in many different areas in physics. I will discuss both conceptual and computational aspects of this idea and give examples of several interacting quantum field theories where it successfully solves the sign problem.

Friday, March 30th 2018

12:30 pm:

We entertain the possibility that a long range force may act on dark matter. The potential coupling of this force to baryons and leptons could lead to new ways of thinking about some of the open questions in particle physics. Here, we mainly focus on scalar forces with various coupling strengths and ranges and examine some of the ways in which they can affect interpretations of dark matter direct detection, neutrino oscillations, or cosmological data.

Friday, April 6th 2018

12:30 pm:

Friday, April 13th 2018

12:30 pm:

There has been substantial progress toward establishing a landscape of non-supersymmetric dualities in three dimensions. These dualities equate Chern-Simons gauge theories coupled to matter, and relate theories of fundamental fermions to those of fundamental bosons. I will discuss a proposal for a new “master” duality between Chern-Simons theory coupled to fundamental bosons and fermions, which if correct summarizes most of these “3d bosonization” dualities.

Friday, April 20th 2018

12:30 pm:

We propose a grand unified SU(5) x U(1)_X model, where the standard SU(5) grand unified theory is supplemented by minimal seesaw and a right-handed neutrino dark matter with an introduction of a global Z_2-symmetry. In the presence of three right-handed neutrinos (RHNs), the model is free from all gauge and mixed-gravitational anomalies. The SU(5) symmetry is broken into the Standard Model (SM) gauge group at M_GUT = 4 x 10^16 GeV in the standard manner, while the U(1)_X symmetry breaking occurs at the TeV scale, which generates the TeV-scale mass of the U(1)_X gauge boson (Z′ boson) and the three Majorana RHNs. A unique Z_2-odd RHN is stable and serves as the dark matter (DM) in the present Universe, while the remaining two RHNs work to generate the SM neutrino masses through the minimal seesaw. We investigate the Z′-portal RHN DM scenario in this model context, and find that the constraints from the DM relic abundance and the search results for a Z′ boson resonance at the Large Hadron Collider (LHC) are complementary to narrow down the allowed parameter region, which will be fully covered by the future LHC experiments (for the Z′ boson mass < 5 TeV). We also briefly discuss the successful implementation of baryogenesis and cosmological inflation scenarios in the present model.

Friday, April 27th 2018

12:30 pm:

How did inflation end? For a broad class of "simple", observationally consistent inflationary models, I will present results regarding: (1) Nonlinear fragmentation and soliton formation in the inflaton field, (2) the equation of state of the universe after inflation. For sufficiently complex models, I will highlight some universal results from stochastic particle production during inflation and reheating, and discuss their implications for initial curvature perturbations from the early universe.

Friday, May 4th 2018

12:30 pm:

Cosmic strings are generic cosmological predictions of many extensions

of the Standard Model of particle physics, such as a *U*(1)^{′}
symmetry breaking phase transition in the early universe or remnants of superstring theory. Unlike other topological defects, cosmic strings can reach a scaling regime that maintains a small fixed fraction of the total energy density of the universe from a very early epoch until today. If present, they will oscillate and generate gravitational waves with a frequency spectrum that imprints the dominant sources of total cosmic energy density throughout the history of the universe. In this talk I will demonstrate that current and future gravitational wave detectors, such as LIGO and LISA, could be capable of measuring the frequency spectrum of gravitational waves from cosmic strings and discerning the energy composition of the universe at times well before primordial nucleosynthesis and the cosmic microwave background where standard cosmology has yet to be tested. This work establishes a benchmark case that gravitational waves may provide an unprecedented, powerful tool for probing the evolutionary history of the very early universe.

Friday, November 23rd 2018

12:30 pm:

Friday, December 7th 2018

12:30 pm:

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