Bruno Valeixo Bento

Welcome to my website!

I am a so-called “theoretical physicist” and my job is to study the Universe. I’m from Cascais (Lisbon), in sunny Portugal, where I started out my journey at Instituto Superior Técnico (UL) before moving to London to get my MSc at Imperial College and then Liverpool for my PhD studies. I am currently in Madrid, doing a postdoc at Instítuto de Física Teórica (IFT).

Not only do I like doing science, but I also love communicating it – I enjoy giving talks, for both experts and non-experts, and telling everyone what I’ve been learning all along (this is something I hope to do more in the future!). You can find more about my outreach and science communication here.

My research in a nutshell

My work is mainly focused on String Theory and Cosmology. I am interested in connecting the high-energy physics of strings to the low-energy observations we want to explain: this includes for example the mysterious dark energy and dark matter that dominate the Universe around us (e.g. in the context of the debate around de Sitter vacua in string theory). I usually do this by exploring compactifications of the extra dimensions of string theory in the presence of things like fluxes and branes, which can have interesting effects – an example is the warping that was the basis of my PhD studies in Liverpool. More recently I have started to think more carefully about the Swampland conjectures and their interplay with the familiar reasoning and intuition of Effective Field Theories. You can find more details on my research here.

latest posts

Jan 29, 2025	EFTs and the Species Scale

2025

EFT & Species Scale: Friends or foes?

Bruno Valeixo Bento, and João F. Melo

Jan 2025

Abs PDF

Recently the notion that quantum gravity effects could manifest at scales much lower than the Planck scale has seen an intense Swamplandish revival. Dozens of works have explored how the so-called species scale – at which an effective description of gravity must break down – relates to String Theory and the Swampland conjectures. In particular, the interplay between this scale and the abundant towers of states becoming lighter in asymptotic regions of moduli spaces has proved to be key in understanding the real scale of quantum gravity. Nevertheless concerns have been raised regarding the validity of using infinite towers of states when estimating this scale within Effective Field Theory and, more precisely, the consistency of cutting the tower part way through in a framework that relies on a clear separation of scales. In this work we take an EFT point-of-view and provide a detailed perturbative derivation of the species scale – by computing the 1-loop graviton propagator in the presence of many fields – thereby clarifying common sources of confusion in the literature. Not only do we clarify the setup, assumptions and regimes of validity of the result, but more importantly apply the same methods to an infinite tower of states. We show how each state in the tower contributes to the species scale and how the procedure of counting only ”light fields” can be compatible with not cutting the tower, thereby maintaining the harmony between infinite towers and EFTs even in the context of the species scale.

latest posts

Recent papers

2025