Personal tools
All Events
Up one levelThis is a list of all the site events in reverse chronological order.

NonLinear Optics of TwoDimensional Materials
(CFP Room, from 20181207 14:00 to 20181207 18:30)  Starting Meeting of the FCT project about NonLinear Optics in TwoDimensional Materials, FCT

On the energy transport in a nonintegrable Ising chain
(CFP Room (326), from 20181107 13:00 to 20181107 14:00)  Typicality arguments have been first proposed as a welldefined framework to study quantum thermodynamics, from a more fundamental point of view. The key idea of typicality is to describe thermal ensembles from a pure state formalism. The applicability of typicality extends beyond equilibrium quantum physics and possibly to other areas of physics. I will present a study of the energy transport in a nonintegrable spin1/2 Ising chain using typicality arguments, which amounts to characterizing the quench dynamics after a local perturbation. We obtained numerical results regarding transport coefficients both at finite and infinite temperature, which question the understanding in nonintegrable models. Second, I will introduce Matrix Product States (MPS) and explain the connection with typicality arguments. We obtained several results regarding typicality of MPS and showed their limitations to study quench dynamics.

Can Teleparallel gravity (TEGR) really be the Translations gauge theory?
(CFP Room (326), from 20181017 13:30 to 20181017 14:30)  I will report on my work reexamining the translation gauge aspect of Teleparallel Equivalent to GR. TEGR is presented as the gravity theory equivalent to GR that is also the gauge theory of translations. We addressed that claim and discovered that it is not tenable given that the principal fiber bundle of translation cannot be built in general and that the need for general frames entails the use of the Lorentz group. We found the solution in a WeitzenbockCartanPoincaré construction that is not yet clearly a gauge theory. This talk is funded by Fundação para a Ciência e a Tecnologia (FCT) through the project UID/FIS/04650/2013.

Planar fourpoint functions of protected operators in N=4 SYM
(CFP Room (326), from 20181015 13:30 to 20181015 14:30)  We study fourpoint functions of protected operators in planar N=4 SYM up to the fiveloop order. We use a lightcone OPE analysis to constrain the integrands and then fix the integrated correlators with input from integrability. The OPE data we extract allows us to determine the triple wrapping correction in the Hexagon approach to threepoint functions, which contributes earlier than expected.

Dark side of the seesaw
(Room 326 (CFP room), from 20181003 14:30 to 20181003 15:30)  I present a model where there is a connection between two apparently uncorrelated sectors, namely neutrino and dark matter. In the model, a scalar field acts as mediator between these two sectors, its vacuum expectation value generating the mass of the dark matter and also taking part in generating neutrino mass. A Z4 symmetry is used, broken by the scalar field vacuum to a remnant Z2 responsible for dark matter stability. The observed light neutrino masses and relic abundance constraint on the dark matter combined lead to predictions of the heavy seesaw scale. This framework to connect dark matter and neutrino sector introduced here is a generic one and can be applied to other possible neutrino mass generation mechanism and different dark matter candidate(s). This talk is funded by Fundação para a Ciência e a Tecnologia (FCT) through the project UID/FIS/04650/2013.

Berry phases and topological physics in onedimensional systems
(CFP Room  326, from 20180726 14:00 to 20180726 15:00)  Topological systems are one of the most active research areas in condensed matter physics. The topological characterization of a condensed matter system relies on mathematical constructs such as the Berry phase, the winding number, or the Chern number. In the first part of the talk, I will explain how the Berry phase can be understood as the first cumulant of a series. We calculate higher order cumulants and reconstruct the underlying distribution of the polarization for the RiceMele model. Our approach allows the visualization of a topological transition, how a system goes between phases with different quantization. In the second part of the talk, I will go through constructing onedimensional analogs of the Haldane and KaneMele models. In the former, the overall winding number does not indicate topological behavior, but the model falls into two independent Creutz models with opposite windings, and the topological transition occurs within each one separately. The latter ladder model also consists of two Creutz models, one for each spinchannel and falls in the CII symmetry class. In its analysis, the thermodynamic derivation of the generalization of the StredaWidom formula to the quantum spin Hall effect turned out to be useful.

Extreme Holography
(CFP Room  326, from 20180725 14:00 to 20180725 15:00)  A massive experimental effort will be devoted in the coming years to the physics of QCD at high energy density and/or high baryon density. Understanding this physics, especially out of equilibrium, is an important theoretical challenge. I will discuss how holography can help us address this challenge. Topics covered will include the farfromequilibrium dynamics near the QCD critical point and colour superconducting phases. No prior knowledge of string theory required.

Optical properties of twodimensional materials
(CFP Room  326, from 20180712 10:30 to 20180712 16:00) 
Nonlinear conductivities of crystals in the independent electron approximation: Results from a velocity gauge analysis
(CFP Room  326, from 20180711 13:30 to 20180711 14:30)  Some formal developments concerning the calculation of nonlinear conductivities of crystals are presented. Even under the simplification of the long wavelength limit and the independent electron approximation, there are subtleties in this calculations, namely on how to deal with particular choices of gauge that define the perturbation. Here, the difficulties inherent to perturbative calculations in the velocity gauge are addressed. In particular, it is shown how, contrary to the common belief in the literature, calculations can be done to any order and for any finite band model in this gauge. The procedure and advantages of the velocity gauge in such calculations are described.

The Analytic Functional Bootstrap I: 1D CFTs and 2D SMatrices
(CFP Room  326, from 20180629 14:00 to 20180629 15:00)  We study a general class of functionals providing an analytic handle on the conformal bootstrap equations in one dimension. We explicitly identify the extremal functionals, corresponding to theories saturating conformal bootstrap bounds, in two regimes. The first corresponds to functionals that annihilate the generalized free fermion spectrum. In this case, we analytically find both OPE and gap maximization functionals proving the extremality of the generalized free fermion solution to crossing. Secondly, we consider a scaling limit where all conformal dimensions become large, equivalent to the large AdS radius limit of gapped theories in AdS2. In this regime we demonstrate analytically that optimal bounds on OPE coefficients lead to extremal solutions to crossing arising from integrable field theories placed in large AdS2