Seminars take place on Wednesdays 12:00-1:00pm in Randall Laboratory #3481
Organizer: Raymond Co
Josephine Suh (Caltech): Statistical mechanics of a two-dimensional black hole | 9/12/18
The dynamics of a nearly-AdS2 spacetime with boundaries can be reduced to that of two particles in the anti-de Sitter space. We determine the class of physically meaningful wavefunctions, and prescribe the statistical mechanics of a black hole. We demonstrate how wavefunctions for a two-sided black hole and a regularized notion of trace can be used to construct thermal partition functions, and more generally, arbitrary density matrices. We also obtain correlation functions of external operators. The talk is based on work with A. Kitaev in the preprint arXiv:1808.07032.
Katelin Schutz (Berkeley): Cosmological signatures of sub-MeV dark matter freeze-in | 9/19/18
Dark matter could be a thermal relic of freeze-in, where the dark matter is produced by extremely feeble interactions with Standard Model particles dominantly at low temperatures. The simplest sub-MeV dark matter models with freeze-in include models with a kinetically-mixed dark photon mediator, or equivalently models where dark matter is millicharged under the Standard Model U(1). In this talk I will discuss how such models can impact and be constrained by cosmological observables, including the CMB, the Lyman-alpha forest, and the EDGES observation of the cosmological 21 cm global signal.
Uri Kol (NYU): Soft Gravitons and Hawking Radiation | 9/26/18
We study the effect of the factorization of infrared dynamics on the process of particle creation near a black hole horizon. We show that the emission of soft particles factors out of the S-matrix in the fixed-background approximation and to leading order in the soft limit. The factorization is implemented by dressing the incoming and outgoing asymptotic states with clouds of soft photons and soft gravitons. We find that while the soft photon cloud has no effect, the soft graviton cloud induces a phase shift in the Bogolyubov coefficients relating the incoming and outgoing modes. However, the flux of outgoing particles, given by the absolute value of the Bogolyubov coefficient, is insensitive to this phase.
Gustavo Tavares (Maryland): Detecting dark matter from Supernovae | 10/31/18
The central region of Supernovae are one of the hottest and densest regions in the Universe. Due to the high temperatures, particles with sub-GeV masses can be copiously produced if they have non-negligible couplings to the Standard Model. If dark matter has sub-GeV mass it will be produced in the hot Supernovae core and it will have sufficiently large momenta to be detectable in direct detection experiments. In this talk I discuss the sensitivity of current and future Xenon based direct detection experiments to a simplified model of dark matter which interacts with the Standard Model via the dark photon portal.
Cody Long (Northeastern University): Lessons from the Landscape | 10/10/18
I will discuss how the string landscape might inform how we think about low energy effective field theories coupled to gravity. By studying the largest-to-date ensembles of geometries for string compactifications, we find several striking generic features: large hidden gauge sectors, regions of strong coupling, and large numbers of light axions. Understanding these ensembles, and the landscape as whole, requires a new set of tools, both formal and computational, including new mathematics and tools from data science, the development of which I will discuss.
David McKeen (TRIUMF): Neutrino-dark matter interactions | 10/24/17
I will describe scenarios where the dark matter couples to neutrinos. This possibility has important implications for structure formation. I will describe novel probes of this possibility at the LHC and intensity frontier facilities. Additionally, the possibility of detecting neutrinos from dark matter decays at future experiments looking for the cosmic neutrino background such as PTOLEMY will be discussed.
Sam McDermott (FNAL): Dark Matter and Fusion: Signals and Constraints from the Dark and the Light | 10/31/17
Over the past several years, non-WIMP dark matter candidates have attracted a surge of interest in the particle physics community. In this two-part talk, I will summarize the underlying physics motivation for (and observable consequences of) two such candidates, which share the feature that they are bound states of more familiar constituents. The first part of the talk will examine the astrophysical implications of a dark fermion that can form two-body bound states. The second part of the talk will examine new constraints on the "dibaryon", a hypothetical QCD bound state of six light quarks. The common thread of the talk will be the unique signals of fusion within or into a dark matter sector.
Eliot Hijano (UBC): Holographic Entanglement and BMS blocks in three dimensional flat space | 11/7/18
I will discuss the holographic construction of entanglement entropy and blocks in three-dimensional flat space-times. I will present a prescription based on world-line methods in the probe limit, inspired by recent analog calculations in AdS/CFT. Building on this construction, a full extrapolate dictionary will be proposed, and used to compute holographic correlators and blocks away from the probe limit. Blocks involving heavy operators will be shown to involve probe particles propagating in flat space cosmologies.
Keisuke Harigaya (IAS): Higgs parity, strong CP problem and unification | 11/14/18
The quartic coupling of the Standard Model Higgs nearly vanishes at a high energy scale. We show that this is explained by the parity symmetry and its spontaneous break down by the condensation of the parity partner of the Higgs. The parity can solve the strong CP problem. The theory is embedded into SO(10) unification and the precise gauge coupling unification is achieved.
Silviu Pufu (Princeton): M-theory and String Theory S-matrix From CFT | 11/21/18
Special Seminar.
David McGady (Niels Bohr Institute): David McGady (Niels Bohr Institute) | 11/28/18
Surprisingly, partition functions for some model systems in statistical mechanics are invariant under formally reflecting the sign of temperature, T: +T -> -T. We call this T-reflection invariance. Clearly, partition functions for generic statistical systems cannot be invariant under T-reflection. However, in this talk we focus on finite-temperature path integrals and give a general picture for why finite-temperature path integrals in quantum field theory *should* behave well under T-reflection. We probe this general picture in the context of the harmonic oscillators (in one-dimension) and in conformal field theories on the two-torus (in two-dimensions) and in the mathematics of modular forms. We find that the relevant path integrals are often invariant only up to overall T-independent phases, which could be naturally interpreted as new anomalies under large coordinate transforms.
Nikita Blinov (FNAL): Cosmology with Sub-MeV Thermal Relics | 12/05/18
The nature of dark matter (DM) is unknown, with a vast array of possibilities able to account for the missing mass of the universe. A predictive subset of DM models has DM in thermal equilibrium with Standard Model particles in the early universe. A well-known example of this is the Weakly-Interacting Massive Particle (WIMP) with an electroweak-scale mass. However, as direct searches for WIMP-nucleus interactions set stronger and stronger limits, attention has turned to less well-explored DM candidates. Sub-MeV thermal relics, in particular, have received little attention, in part due to the apparently stringent bounds from astrophysics and cosmology. For example, such particles contribute to the energy density of the universe at the time of nucleosynthesis and recombination. The resulting constraints on extra degrees of freedom typically exclude even the simplest of such dark sectors. I will describe the physics that leads to these bounds and show that if a sub-MeV dark sector entered equilibrium with the Standard Model after neutrino-photon decoupling, these constraints are alleviated. This scenario naturally arises in theories of neutrino mass generation through the spontaneous breaking of lepton number. Dark matter relic abundance in these models independently motivates the MeV scale. This scenario will be decisively tested by future measurements of the cosmic microwave background and large scale structure of the universe.
