Níck

theoretical physicist


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Seminars

I have presented many seminars throughout the years. This is a list of my favorites. They are accompanied by video recordings, lecture notes, slideshows, etc whenever possible. Seminars are chronologically ordered, with older entries at the bottom of the page.

Negative Masses are Unstable

and we don't need energy conditions to prove it

Abstract: We studied negative-mass, spherically symmetric stars made of ideal barotropic fluids. After considering linear perturbations away from staticity, we learned that all such models are unstable. Thus, we found a completely classical explanation for the absence of negative masses. While all previous positive mass theorems assume microscopic positivity of mass in some sense, ours does not.

Tags: General Relativity and Energy Conditions

This seminar was originally presented in Portuguese at the XLVII Congresso Paulo Leal Ferreira de Física, while the poster was originally presented at the Witnessing Quantum Aspects of Gravity in a Lab conference.

Slideshow: available here (in English with commentary)

Poster: available here (in English)

Related publications:

  • Aguiar Alves, Níckolas de, André G. S. Landulfo, and Bruno Arderucio Costa. “Positive Mass in General Relativity Without Energy Conditions,” 2024. Submitted. arXiv: 2408.00154 [gr-qc]. Summarized here.

The Memory Effect and What It Means for Humankind

(or Don't Forget About Memory)

Abstract: The memory effect is a prediction in classical general relativity that consists of the fact that, upon the passage of a gravitational wave, a pair of nearby inertial detectors will be permanently displaced. In this seminar, I will review the basic ideas behind the linear memory effect and discuss how it is connected to other infrared aspects of general relativity, such as Weinberg’s soft graviton theorem and the Bondi–Metzner–Sachs group.

Tags: General Relativity and Infrared Structure of Field Theories

This is a one-hour long seminar originally presented at my group's journal club and at the São Paulo Research Group meetings in Astro & Cosmo.

Slides with commentary: click here


Nonperturbative Renormalization Group Flow for a Particle Detector

Abstract: The functional renormalization group is a powerful tool to study nonperturbative physics, but it has not been much explored within quantum field theory in curved spacetime yet. On the other hand, particle detectors are an omnipresent tool within quantum field theory in curved spacetime and relativistic quantum information but are often treated only perturbatively. In this paper, we present the first computation of the functional renormalization group flow for a particle detector. The chosen model is an inertial Unruh–DeWitt detector in Minkowski spacetime, for simplicity. A new development in heat kernel techniques—the Taylor trick—is necessary to perform the calculations and it is important to carefully choose cutoffs that diverge at the ultraviolet limit to keep the beta functions finite. We compare our results with the MS-bar results at one-loop and find that both computations agree qualitatively, as expected.

Tags: Quantum Field Theory in Curved Spacetime and Functional Renormalization Group

This is a twenty-minute long seminar originally presented at the Golden Wedding of Black Holes and Thermodynamics. It is also a poster presented on many different occasions.

Slideshow: available here

Poster: available here (also on Figshare)

Related publications:

  • Aguiar Alves, Níckolas de (2023). “Nonperturbative Aspects of Quantum Field Theory in Curved Spacetime”. MSc thesis. Santo André, Brazil: Federal University of ABC. xxiv, 152 pp. arXiv: 2305.17453 [gr-qc]. Summarized here.