Conference

I will show how to derive new positivity bounds for scattering amplitudes in theories with a massless graviton in the spectrum in four spacetime dimensions. The bounds imply that extremal black holes are self-repulsive, M/|Q|<1 once higher dimensional operators are taken into account, and that they are unstable to decay to smaller extremal black holes, hence providing an S-matrix proof of the weak gravity conjecture.

The discovery of gravitational waves from a binary black hole merger in 2015 opened up a new window to study the Universe, including the origin of black holes, the nature of dark matter, and the expansion history of the Universe. However, gravitational waves emitted from binary mergers propagate through the inhomogeneous Universe, which can have a considerable impact on observations of gravitational waves, in good or bad ways. I will highlight some examples of the effects of the inhomogeneity on gravitational wave observations, including their possible applications and implications.

I will introduce our recent proposal that the state of the universe does *not* spontaneously violate CPT. Instead, the universe after the big bang is the CPT image of the universe before it, both classically and quantum mechanically. The pre- and post-bang epochs comprise a universe/anti-universe pair, emerging from nothing directly into a hot, radiation-dominated era. CPT symmetry selects the QFT vacuum state on such a spacetime, providing a new interpretation of the cosmological baryon asymmetry, as well as a particularly economical explanation for the cosmological dark matter. Requiring only the standard three-generation model of particle physics (with right-handed neutrinos), a Z_2 symmetry suffices to render one of the right-handed neutrinos stable. We calculate its abundance from first principles: matching the observed dark matter density requires its mass to be 4.8 x 10^{8} GeV. Several other testable predictions immediately follow: e.g. (i) the lightest neutrino is massless; (ii) neutrinoless double beta decay occurs at a specific rate; and (iii) there are no primordial long-wavelength gravitational waves. The proposal also has interesting things to say about the strong CP problem, the observed electrodynamic arrow of time, cosmological boundary conditions, and the wave-function of the universe. (Based on arXiv:1803.08928, arXiv:1803.08930, and forthcoming work.)

We study the quantum work associated with the nonequilibrium quench of an optical lattice as it evolves from initial Mott type states with large potential barriers under the Sine-Gordon Hamiltonian that describes the dynamics of the system when the barriers are suddenly lowered. The calculations are carried out by means of the Boundary Bethe Ansatz approach where the initial and final states of the quench are applied as boundary states on the evolving system. We calculate exactly the Loschmidt amplitude, the fidelity and work distribution characterizing the quenches for different values of the interaction strength.

We probe a generic two dimensional conformal interface via a collider experiment. We measure the energy and charges which are reflected and transmitted through the interface. If the largest symmetry algebra is Virasoro, the average transmitted energy is independent of the details of the initial state, and is fixed in terms of the central charges and of the two-point function of the displacement operator. The situation is more elaborate when extended symmetries are present. We comment on the bounds imposed by positivity of the total energy flux at infinity, and on applications of the result to the physics of steady states.

I will discuss entanglement negativity, an entanglement measure for mixed quantum states, in many-body systems, including lattice quantum systems and quantum field theories. I will also discuss the possible holographic dual description of entanglement negativity in field theories and tensor networks.

The shape deformation of conformal defects is implemented by the displacement operator. In this talk we consider superconformal defects and we provide evidence of a general relation between the two-point function of the displacement and the one-point function of the stress tensor operator. We then discuss the available techniques for the computation of this one-point function. First, we show how it can be related to a deformation of the background geometry. Then we conclude with a discussion of surface defects in four-dimensional N=2 theories, where the chiral algebra provides an additional powerful tool.

The g-theorem is a prominent example of C-theorems in two-dimensional boundary CFT and the extensions are conjectured to hold in higher-dimensional BCFTs. On the other hand, much less is known for C-theorems in a CFT with conformal defects of higher codimensions. I will investigate the entanglement entropy across a sphere and sphere free energy as a candidate for a C-function in DCFT, and show they differ by a universal term proportional to the vev of the stress tensor. Based on this relation, I will propose to use the sphere free energy as a C-function in DCFT. This proposal unifies the previously known theorems and conjectures, and passes several checks, including a few examples in field theories and a holographic proof in simple gravity dual models of DCFTs.