#physics answers

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## UPCOMING EVENTS

- PRT SEM: Masaki Yamada (TUFTS) Strongly interacting massive particle (SIMP) and a strong U(1) gauge theory

Start: 04:15pm – End: 05:15pm- 04:15pm

“A strongly interacting massive particle (SIMP) is a good candidate for dark matter (DM) because its self-interaction can address some astrophysical offsets, such as the “core vs cusp” problem and the “too-big-to-fail” problem. A low energy effective theory of a strongly interacting non-Abelian gauge theory gives a simple realization of the SIMP mechanism in a dark sector, though we need to introduce a nontrivial interaction between the Standard Model (SM) sector and the dark sector to maintain kinetic equilibrium. In this talk, I will first explain a SIMP model in a strong non-Abelian gauge theory with a singlet field in the hidden sector. Assuming a mixing between the singlet field and the SM Higgs field, we can maintain the kinetic equilibrium between the hidden and SM sectors. The mixing effect leads to signals for future collider experiments, direct DM detection experiments, and beam-dump experiments. Then I will explain a SIMP model in an Abelian gauge theory that is confined due to a monopole condensation. This model is much simpler because the monopole plays the roles of U(1) confinement and mediator between the hidden and SM sectors.”

- CMP Special Seminar: Arbel Haim (The Weizmann Institute), hosted by Bertrand Halperin

Start: 03:00pm – End: 04:30pm- 03:00pm

Title: “Current aspects of topological superconductivity”

Abstract: Recent experiments have provided mounting evidence for the existence of Majorana bound states (MBSs) in condensed-matter systems. Until the long-term goal of braiding MBSs is achieved, one is prompted to ask: what is the next step in the study of topological superconductivity and MBSs? In my talk I will discuss two topics relating to this question. In the first part I will examine the possibility of, not only detecting the Majoranas, but also witnessing some of their exotic properties. In particular their non-local nature, or in other words, the fact that the MBS is half a fermion whose occupation is encoded in a nonlocal way. I will show that current cross correlations in a T-junction with a single MBS exhibit universal features, related to the Majorana nonlocality. This will be contrasted with the case of an accidental low-energy Andreev bound state. In the second part I will discuss the possibility of realizing a different topological phase hosting MBSs in currently available experimental platforms. This will be a topological superconducting phase which is protected by time-reversal symmetry, and which is characterized by having a Kramers’ pair of MBSs at each end. As I will discuss, repulsive interactions are a necessary ingredient for the realization of this phase. I will present a mechanism, based on the interplay between repulsive interactions and proximity to a conventional superconductor, which drives the system into the topological phase. The effect of interactions is studied analytically using both a mean-field approach and the renormalization group. We corroborate our conclusions numerically using DMRG.

[1] Arbel Haim, Anna Keselman, Erez Berg, Yuval Oreg, Phys. Rev. B, 89, 220504(R) (2014)

[2] Arbel Haim, Erez Berg, Felix von Oppen, Yuval Oreg, Phys. Rev. B, 92, 245112 (2015)

[3] Arbel Haim, Erez Berg, Felix von Oppen, Yuval Oreg, Phys. Rev. Lett. 114, 166406 (2015)

[4] Arbel Haim, Konrad Wölms, Erez Berg, Yuval Oreg, Karsten Flensberg, Phys. Rev. B 94, 115124 (2016)

[5] Arbel Haim, Erez Berg, Karsten Flensberg, Yuval Oreg, arXiv:1605.07179

Thursday, October 27th

- CMP Seminar: Victor Galitski (University of Maryland), hosted by Eugene Demler

Start: 12:00pm – End: 01:00pm- 12:00pm

Title: Soliton motion, dissipation, and death in quantum superfluids

Abstract: Solitons are fascinating non-linear phenomena that occur in a diverse array of classical and quantum systems. In particular, they are known to exist in quantum superfluids, and have been demonstrated experimentally in Bose-Einstein condensates and fermionic superfluids. In this talk, I will first review the general theory of solitons in superfluids and present an exact solution to the problem of a moving soliton in a one-dimensional superconductor. Connections to the inverse scattering method and supersymmetric quantum mechanics will be emphasized. Using these exact methods, the full soliton spectrum will be derived along with its “inertial” and “gravitational” masses. The former will be shown to be orders of magnitude larger than the latter. This results in slow motion of the soliton, consistent with recent MIT experiments. In the second part of my talk, I will discuss the soliton decay and derive the quasiclassical equations of motion containing a non-local in time friction force. Interestingly, Ohmic friction is absent in the integrable setup and the Markovian approximation gives rise to the Abraham-Lorentz force (i.e. a term proportional to the derivative of the soliton’s acceleration), which is known from classical electrodynamics of a charged particle interacting with its own radiation. These Abraham-Lorentz equations famously contain a fundamental causality paradox, where the soliton/particle interacts with excitations/radiation originating from future events. We show, however, that the causality paradox is an artifact of the Markovian approximation, and our exact non-Markovian dissipative equations give rise to physical trajectories. In the end, I will show results of recent experiment that observed soliton diffusion and decay in superfluids, well described by our theory.

Relativistic electron scattering and QED

Abstract:

The results of non-perturbative relativistic electron-atom scattering calculations are presented. Hans Bethe’s work on relativistic electron scattering in the 1930’s is also discussed, together with various historical aspects of Enrico Fermi’s and Bethe’s early QED papers. The evolution of ideas related to the use of renormalization in quantum field theory are outlined.

Start: 04:15pm – End: 05:15pm

- 04:15pm
We present the foundation for a holographic dictionary with depth perception. The dictionary consists of natural operators associated with CFT bilocals whose duals are simple, diffeomorphism-invariant bulk operators. These objects admit a description as fields in kinematic space, a phase space for such probes. The framework of kinematic space allows for conceptually simple derivations of many results known in the literature, including linearized Einstein’s equations, the relationship between conformal blocks and geodesic Witten diagrams, and the CFT representation of bulk local operators. Reference: https://arxiv.org/abs/1604.03110

Friday, October 28th

Monday, October 31st

- Ali Yazdani (Princeton): Loeb Lecture in Physics: Spotting the elusive Majorana under the microscope

Start: 04:15pm – End: 06:15pm- 04:15pm
- View in Google Calendar

- Loeb Colloquium: Ali Yazdani (Princeton), Visualizing a nematic quantum liquid

Start: 04:15pm – End: 06:00pm- 04:15pm

The MORRIS LOEB LECTURES IN PHYSICS SERIES

Speaker: Ali Yazdani,

Class of 1909 Professor of Physics,

Director of the Princeton Center for Complex Materials

Princeton UniversityThe lecture is free and open to the public

https://www.physics.harvard.edu/events/loeb

- Ali Yazdani (Princeton): Loeb Lecture in Physics: Spotting the elusive Majorana under the microscope