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Friday, January 25th 2019

12:30 pm:

Friday, February 1st 2019

12:30 pm:

I will discuss a class of models in which thermal dark matter is lighter than an MeV. If dark matter thermalizes with the Standard Model below the temperature of neutrino-photon decoupling, constraints from measurements of the effective number of neutrino species are alleviated. This framework motivates new experiments in the direct search for sub-MeV thermal dark matter and light force carriers.

Friday, February 8th 2019

12:30 pm:

The particle that makes up the dark matter of the universe could be an axion. A significant fraction of the axion dark matter could be in the form of bound Bose-Einstein condensates of axions. The condensates are called "axion stars" if they are bound by gravity and "oscillons" if they are self-bound. There may be aspects of axion dark matter in which the effects of axion stars and oscillons have not been fully taken into account.

Friday, February 15th 2019

12:30 pm:

A variety of experimental efforts are currently underway to detect ultra-light dark photon dark matter — a spin-1 particle dark matter candidate with mass below 1 eV. However, dark photon dark matter has a notorious production problem: it is challenging to write down a model that yields the correct relic abundance of non-relativistic dark photons. In this talk I will discuss how dark photon dark matter is created from a network of near-global, Abelian-Higgs cosmic strings. These strings are expected to survive in the universe today, and their motions create a stochastic gravitational wave noise.

Friday, February 22nd 2019

12:30 pm:

Friday, March 1st 2019

12:30 pm:

Halometry---mapping out the spectrum, location, and kinematics of nonluminous structures inside the Galactic halo---can be realized via effects that variable weak gravitational lensing induces on the proper motions of stars and other luminous background sources. Modern astrometric surveys provide unprecedented positional precision along with a leap in the number of cataloged objects. Astrometry thus offers a new and sensitive probe of collapsed dark matter structures over a wide mass range, from one millionth to several million solar masses. It opens up a window into the spectrum of primordial density fluctuations with very small comoving wavenumbers, scales hitherto poorly constrained.

I will outline several detection strategies for dark matter substructure based on time-domain weak gravitational lensing, after summarizing existing techniques and constraints. I will present preliminary results from ongoing analyses based on Gaia's second data release. Finally, I will show that minimal models of axion-like dark matter naturally produce dense small-scale structures which can probed by the aforementioned astrometric lensing techniques.

Friday, March 8th 2019

12:30 pm:

I will present a mechanism of leptogenesis

which is based on the vacuum CP-violating phase transition. This approach

differs from classical thermal leptogenesis as a specific seesaw model, and

its UV completion, need not be specified. The lepton asymmetry is generated

via the dynamically realised coupling of the Weinberg operator during the

phase transition. This

mechanism provides strong connections with low-energy neutrino experiments.

Friday, March 15th 2019

12:30 pm:

Friday, March 22nd 2019

12:30 pm:

Friday, March 29th 2019

12:30 pm:

We consider the quantum partition function for a system of quantum spinors and then derive an equivalent (or dual) classical partition function for some scalar degrees of freedom. The coupling between scalars is non-trivial (e.g. a model on 2-sphere configuration space), but the locality structure of the dual system is preserved, in contrast to the imaginary time formalism. We also show that the measure of integration in the classical partition function can be formally expressed through relativistic Green's functions which suggests a possible mechanism for the emergence of a classical space-time from anti-commutativity of quantum operators.

Friday, April 5th 2019

12:30 pm:

The conventional misalignment mechanism can explain axion dark matter only in a limited mass range and face various difficulties for vector dark matter that we refer to as dark photons. For the former case, we provide a dynamical explanation for an initial condition near the hilltop or the bottom of the potential, which allows for a much wider mass range. Additionally, we propose new dark matter production mechanisms for axions and dark photons via parametric resonance and tachyonic instability, respectively. These ideas expand the parameter space to the regions of interest for the extensive experimental searches.

Friday, April 12th 2019

12:30 pm:

We first review the zero-form/one-form ’t Hooft anomaly matching conditions, using the example of the charge-Q massless Schwinger model. This is the simplest quantum field theory with such anomalies and their manifestation can be seen from different points of view. We will then argue that the Q=2 case and its various generalizations are relevant for the physics of domain walls in four-dimensional super-Yang-Mills theory and adjoint QCD and will show how various aspects of bulk/domain wall interactions found earlier via string theory can be seen in a purely field theoretic setting.

Friday, April 19th 2019

12:30 pm:

I will review the Weak Gravity Conjecture (WGC) and related ideas (such as the Swampland Distance Conjecture and “tower” versions of the WGC), which aim at characterizing generic properties of quantum gravity theories that can be used to diagnose when a low-energy effective field theory cannot be completed into a consistent gravitational theory. As one application, I will explain how arguments based on these conjectures suggest that a theory of quantum gravity requires the photon to be exactly massless.

Friday, April 26th 2019

12:30 pm:

Friday, May 3rd 2019

12:30 pm:

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