Journal Club

Título: Instabilidade Gravitavional em Universo estático e em expansão

Resumo: Neste seminário será apresentado o mecanismo de formação de estrutura via instabilidade gravitacional. A partir de uma aproximação de fluido perfeito para o Universo, partiremos de uma descrição newtoniana em um universo estático fazendo uso da teoria de perturbação para encontrar o crescimento da densidade de matéria neste. No caso do Universo em expansão faremos um tratamento análogo, seguida de uma investigação da densidade de matéria na presença de radiação e energia escura.

Palestrante: Amanda Maria Fonseca
Quando? dia 02/06/2021
Que horas? 16h
Onde: https://meet.google.com/xie-ujhf-bwq

SEMINAR

Testing Gravity with Large-Scale Structures

In the past few decades, cosmology has made impressive progress both theoretically and observably. These advances have been crucial in establishing a standard cosmological model called the ΛCDM model. Although the success of the ΛCDM model is justified, since it has been exhaustively confronted with several different empirical tests, it remains unsatisfactory and incomplete on the theoretical level. Currently, one of the biggest questions in cosmology is to understand the physical origin of the late acceleration of the universe. Two classes of models emerge as an attempt to explain this phenomenon. The first requires the introduction of a dark energy component as a source of acceleration. The second class contains models that modify general relativity on a large scale, in such a way that gravity itself is responsible for the acceleration of the universe. Since the two types of models can reproduce exactly the same expansion story, it is not possible to discriminate them based on this single observation. It is therefore necessary to go beyond the expansion of the universe and to observe the growth of structures to distinguish the dark energy models from those of modified gravity. The aim of this thesis is to build observables sensitive to the growth of structures and therefore to use them to test the theory of gravity. As we show, this can be done both in the linear and non-linear gravity regime. In the linear regime, we offer two tests, which target two different properties of the theory of gravity. In the nonlinear regime, we use a new observable, called the line correlation function, to extract information beyond the power spectrum and improve the gravity tests.

Speaker: Felipe Oliveira Franco

Link: https://meet.google.com/xie-ujhf-bwq

Dia 12/05, às 16h

SEMINAR

1+1 Compactified Boson

The compactified boson consists of a theory for a free massless scalar boson defined from the cylinder to the circle. Because of the nontrivial topological spaces, interesting physical properties emerge, such as topological conserved currents and charges, T-duality and bosonization. To further explore these characteristics, some conformal tools are necessary. In this seminar, I expect to talk about some key notions of Conformal Field Theory, introduce the compact boson and explore its physical implications.

By Victor Hugo Marques Ramos
Mestrando em Física – UEL

When? 30/04/2021
What time? 14 p. m.
Join zoom meeting:

https://us02web.zoom.us/j/89653520467?pwd=VWp3RVcrNUxKN1dINnkxZExMOTF0Zz09

SEMINAR

Effective Theory in the Lifshitz Point: the O(N) and the Non-Linear Sigma Models with z=2.

Systems involving competing interactions and frustration may provide a phase diagram containing an ordered, disordered and modulated phases, and if this three phases coexisting at some point we call this meeting as Lifshitz point. It has very interesting properties, e.g., the dispersion relation at low energies is non-relativistic at this point, what requires a generalization of the Coleman (and Hohenberg-Mermin-Wagner) theorem and a careful counting of the Nambu-Goldstone bosons. In this seminar I want to share some recent advances in our studies about the Lifshitz effective theories with anisotropy degree characterized by the dynamical exponent z=2. Defining the competing interaction from first, second and diagonal neighbors in the spherical model, I will show some statistical results and its connection with the Non-Linear Sigma Model. I want to comment some technical aspects of the anisotropic Non-Linear Sigma and anisotropic O(N) Models, the renormalization procedure and how to find the critical exponents. Finally, I want to show the possible connection of this two anisotropic models at large-N, as occurs in the usual relativistic case.

By Heitor Casaçola Cinel
Doutorando em Física – UEL

When? 16/04/2021
What time? 16 p. m.
Join zoom meeting:

https://us02web.zoom.us/j/89653520467?pwd=VWp3RVcrNUxKN1dINnkxZExMOTF0Zz09

SEMINAR

C-Theorem: Proof and Applications

Zamolodchikov’s C-theorem is one of the many remarking results in two dimensional quantum field theories, it formalizes the notion that some information is lost along the RG flow as we integrate out the high energy degrees of freedom. In this seminar we will discuss how to prove this theorem and two examples on how to use it.

By Rodrigo Corso
Ph. D. Student

When? 26/03/2021
What time? 14 p. m.
Join zoom meeting:

https://us02web.zoom.us/j/89653520467?pwd=VWp3RVcrNUxKN1dINnkxZExMOTF0Zz09

SEMINAR

Symmetry Protected Topological Orders

The study of topological phases of matter seeks to describe and understand an extensive range of phenomena present in quantum materials. Although all these phases present topological properties, they are not all “topologically ordered”. Important examples of topologically non-ordered phases are the Symmetry Protected Topological (SPT) ordered phases. SPT orders present topological aspects only if the system is invariant under some symmetry group. Otherwise, if the symmetry is explicitly or spontaneously broken, the topological properties vanish. In this seminar, I intend to talk about the general aspects of SPTs and present an exactly solvable lattice model for a 2D SPT spin system as an attempt to provide some intuition on the physics of such phases.

By Guilherme Delfino Silva
Ph. D. Student

When? 12/03/2021
What time? 1:30 p.m.
Join Zoom Meeting:

https://us02web.zoom.us/j/89653520467?pwd=VWp3RVcrNUxKN1dINnkxZExMOTF0Zz09

Seminar

Effective descriptions of fracton phases

Fractons are an exotic quasiparticle that lacks a property assumed to be inherent of all particles: the ability to move. Quite often fracton phases are separated into type-I, in which bound states can move obeying certain rules, and type-II, in which all particles are strictly localized and immobile. The motivation to study these phases comes from the fact that they appear in a variety of physical settings, ranging from spin liquids to gravity, also they fail to fit in the standard modern framework to describe quantum matter. Therefore, they represent a new interesting challenge to overcome. In this seminar we give a “bird’s eye” view on these exotic phases focusing on what has been done so far in the field and exploring some possible routes for the future.

By Weslei Fontana
Ph. D. Candidate

When? 26/02/2021 What time? 2 p.m.

Join Zoom Meeting: https://us02web.zoom.us/j/83707086196pwd=dEx5YVdvbGtXSW9RV0Z1ejBDZXh6QT09

Defence of M.Sc dissertation of Guilherme Delfino Silva

The Theoretical Physics Group at UEL invites everyone to

Defence of M.Sc dissertation

Candidate: Guilherme Delfino Silva

Title: Effective Field Theories for Quantum Spin Liquids and Fractonic Systems

Defence commitee

Prof. Dr. Pedro Rogério Sérgi Gomes – UEL

Prof. Dr. Carlos André Hernaski – UTFPR

Prof. Dr. Rodrigo Gonçalves Pereira – UFRN

When? 12/02

What time? 14 p.m.

Join Zoom Meeting:

https://us02web.zoom.us/j/84042916613?pwd=eDBVU1NqSTNWYktCdTQwbHRyUWlJZz09

Meeting ID: 840 4291 6613

Passcode: YrPS7G