Scientific Series

We revisit the physics of neutrino magnetic moments, focusing in particular on the case where the right-handed, or sterile, neutrinos are heavier (up to several MeV) than the left-handed Standard Model neutrinos. The discussion is centered around the idea of detecting an upscattering event mediated by a transition magnetic moment in a neutrino or dark matter experiment. Considering neutrinos from all known sources, as well as including all available data from XENON1T and Borexino, we derive the strongest up-to-date exclusion limits on the active-to-sterile neutrino transition magnetic moment. We then study complementary constraints from astrophysics and cosmology, performing, in particular, a thorough analysis of BBN. We find that these data sets scrutinize most of the relevant parameter space. Explaining the XENON1T excess with transition magnetic moments is marginally possible if conservative assumptions are adopted regarding the supernova 1987 A and CMB constraints. Finally, we discuss model-building challenges that arise in scenarios that feature large magnetic moments while keeping neutrino masses well below 1 eV. We present a successful ultraviolet-complete model of this type based on TeV-scale leptoquarks, establishing links with muon magnetic moment, B physics anomalies, and collider searches at the LHC.

SNO+ is a multi-purpose, low background liquid scintillator detector located in the SNOLAB facility. This talk will present our progress towards the main goal of SNO+: probing the mass and nature of neutrinos through a search for neutrino less double beta decay. By loading large amounts of natural tellurium into a homogeneous liquid scintillator detector SNO+ is pioneering an affordable and extendable approach to this rare decay search with the isotope 130Te. I will also discuss other physics reach of SNO+ including reactor, solar and supernova neutrinos and invisible nucleon decay. I will present the results for previous water phase operations and the current status of scintillator filling, tellurium plant preparation and background studies.

The quest for non-Abelian quasiparticles has inspired decades of experimental and theoretical efforts. Among their clearest signatures is a thermal Hall conductance with quantized half-integer value. Such a value was indeed recently observed in a quantum-Hall system at ν=5/2 and in the magnetic insulator α-RuCl3. I will explain that a non-topological "thermal metal" phase that forms due to quenched disorder may disguise as a non-Abelian phase by well approximating the trademark quantized thermal Hall response. Remarkably, the quantization here improves with temperature, in contrast to fully gapped systems. In my talk, I will provide analytical and numerical evidence for this effect and discuss its possible implications for the aforementioned experiments.

What factors drive the growth and decay of a pandemic? Can a study of community differences (in demographics, settlement, mobility, weather, and epidemic history) allow these factors to be identified? Has “herd immunity” to COVID-19 been reached anywhere? What are the best steps to manage/avoid future outbreaks in each community?  We analyzed the entire set of local COVID-19 epidemics in the United States; a broad selection of demographic, population density, climate factors, and local mobility data, in order to address these questions. What we found will surprise you! (based on arXiv:2007.00159)

On Monday July 20th, we announced the final results from extended Baryon Oscillation Spectroscopic Survey (eBOSS), the last large-scale structure galaxy survey to be undertaken within the umbrella of the Sloan Digital Sky Survey (SDSS). This marks the culmination of 20 years of galaxy surveys undertaken using the Sloan Foundation Telescope. In this seminar I will summarise the measurements presented in the 23 scientific papers that were released last Monday, and present the impact of the measurements from eBOSS and previous SDSS galaxy surveys on the development of the standard cosmological model.

The sign problem is a widespread numerical hurdle preventing us from simulating the equilibrium behaviour of many interesting models, most notably the Hubbard model. Research aimed at solving the sign problem, via various clever manipulations, has been thriving for a long time with various recent exciting results. The complementary question, of whether some phases of matter forbid the existence of any sign-free microscopic model, has received attention only recently. In this talk, I’ll review recent progress and discuss a novel and quite general criteria we obtained for when a topological quantum field theory has no sign-free microscopic model. I’ll also point out relations to sign problems in frustrated magnets and to the notion of quantum supremacy.

The searches for solving the greatest mysteries of our Universe require ultra-sensitive detectors and an extreme control of the environment and the background in order to detect a rare signal. Over the last decades, technologies have reached such unprecedented sensitivity levels that never-before-seen background signals must be considered. In this talk I will give an overview of the requirements for low background detection and what are the current R&D effortsfor developing new cutting-edge technologies in order to address the common challenges of experiments and for pushing the limits of detector performance.

In the first part of the talk I will present how to compute anomalous dimensions of EFT operators using on-shell scattering amplitudes. The method is used to compute some two loop transitions, which are important to provide a complete characterisation of the dynamics affecting some low energy precision experiments. In the second part, I show how unitarity, analycity and locality impose stringent non-trivial constraints to the space of possible EFTs, invisible at the Lagrangian level by only considering the symmetries of the IR theory.

The standard cosmological model determined from the accurate cosmic microwave background measurements made by the Planck satellite implies a value of the Hubble constant H0 that is 4.2 standard deviations lower than the one determined from Type Ia supernovae. The Planck best fit model also predicts lower values of the matter density fraction Om and clustering amplitude S8 compared to those obtained from the Dark Energy Survey Year 1 data. We show that accounting for the enhanced recombination rate due to additional inhomogeneities in the baryon density can solve both the H0 and the S8-Om tensions. The additional baryon inhomogeneities can be induced by primordial magnetic fields present in the plasma prior to recombination. The required field strength to solve the Hubble tension is just what is needed to explain the existence of galactic, cluster, and extragalactic magnetic fields without relying on dynamo amplification. Our results show clear evidence for this effect and motivate further detailed studies of primordial magnetic fields, setting several well-defined targets for future observations.

Condensed matter physics is the study of the complex behaviour of a large number of interacting particles such that their collective behaviour gives rise to emergent properties. We will discuss some interesting quantum condensed matter systems where their intriguing emergent phenomena arise due to strong coupling. We will revisit the Landau paradigm of Fermi liquid theory and hence understand the properties of the non-Fermi liquid systems which cannot be described within the Landau framework, due to the destruction of the Landau quasiparticles. In particular, we will focus on critical Fermi surface states, where there is a well-defined Fermi surface, but no quasiparticles, as a result of the strong interactions between the Fermi surface and some massless boson(s). We will outline a framework to extract the low-energy physics of such systems in a controlled approximation, using the tool of dimensional regularization.

Zoom Link:  https://pitp.zoom.us/j/93581608531?pwd=d3NRQXRGNTNISkhuWmxLYkJMZllTUT09

Based on recent work arXiv:1902.08207 and arXiv:1911.02018 with E. Verlinde.

The discovery of gravitational wave signals from merger events of massive binary-black-hole (BBH) systems have prompted a renewed debate in the scientific community about the existence of primordial black holes (PBHs) of O(1-100) solar masses. These objects may have formed in the early Universe and could constitute a significant portion of the elusive dark matter that, according to standard cosmology, makes up the majority of the matter content in the universe. I will review the most recent developments of this field, with focus on multi-messenger prospects of detection. In the first part of the talk, I will present the prospects of discovery for both a hypothetical PBH population and the guaranteed population of astrophysical isolated black holes in our Galaxy, based on the radio and X-ray emission from the interstellar gas that is being accreted onto them (the “shiny dresses”). A future detection will be possible thanks to the expected performance of forthcoming radio facilities such as SKA and ngVLA. Then, I will turn my attention to scenarios where primordial black holes constitute a sub-dominant component of the dark matter, and study the impact of dark matter mini-spikes that are expected to form around them (the “dark dresses”) on several observables. In this context, I will first present an updated computation of the PBH merger rate as a function of DM fraction and redshift that takes into account the impact of the dark dresses. Then, I will discuss the observational prospects of these dresses in binary systems composed of a stellar-mass and an intermediate-mass black hole: I will show a novel calculation of the dephasing of the gravitational waveform induced by the DM spike, potentially detectable with the LISA space interferometer.DARK AND SHINY DRESSES AROUND BLACK HOLES DANIELE GAGGERO (UAM)July 6, 2020 Zoom Line: https://laurentian.zoom.us/j/92591146494