Physics

The idea that structure in the Universe was created from quantum mechanical vacuum fluctuations during inflation is very compelling, but unproven. Finding a test of this proposal has been challenging because the universe we observe is effectively classical. I will explain how quantum fluctuations can give rise to the density fluctuations we observe and will show that we can test this hypothesis using the statistical properties of maps of the universe.

One of the major themes of the modern condensed matter physics is the study of materials with nontrivial electronic structure topology. Particularly significant progress in this field has happened within the last decade, due to the discovery of topologically nontrivial states of matter, that have a gap in their energy spectrum, namely Topological Insulators and Topological Superconductors. In this talk I will describe the most recent work, partly my own, extending the notions of the nontrivial electronic structure topology to gapless states of matter as well, namely to semimetals and even metals. I will discuss both the theoretical concepts, and the recent experimental work, realizing these novel states of condensed matter.

In most materials, electrons fill bands, starting from the lowest kinetic energy states. The Fermi level is the boundary between filled states below and empty states above. This is the basis for our very successful understanding of how metals and semiconductors work. But what if all the electrons within a band had the same kinetic energy (this situation is called a "flat band")? Then electrons could arrange themselves so as to minimize their Coulomb repulsion, giving rise to a wide variety of possible states including superconductors and magnets. Until recently, flat bands were achieved only by applying large magnetic fields perpendicular to a 2D electron system; in this context they are known as Landau levels. Fractional quantum hall effects result from Coulomb-driven electron arrangement within a Landau level. Recently, Pablo Jarillo-Herrero of MIT and coworkers demonstrated flat minibands in graphene-based superlattices, discovering correlated insulators and superconductors at different fillings of these minibands. We have now discovered dramatic magnetic states in such superlattice systems. Specifically, in magic-angle twisted bilayer graphene which is also aligned with a hexagonal boron nitride (hBN) cladding layer, we observe a giant anomalous Hall effect as large as 10.4 kΩ, and signs of chiral edge states. This all occurs at zero magnetic field, in a narrow density range around an apparent insulating state at 3 electrons (1 hole) per moiré cell in the conduction miniband [1]. Remarkably, the magnetization of the sample can be reversed by applying a small DC current. Although the anomalous Hall resistance is not quantized, and dissipation is significant, we suggest that the system is essentially a "Chern insulator", a type of topological insulator similar to an integer quantum Hall state. In a quite different superlattice system, ABC-trilayer graphene aligned with hBN, again near 3 electrons (1 hole) per moiré cell a Chern insulator emerges [2]. This time the flat band is a valence miniband, and a magnetic field of order 100 mT is needed to quantize the anomalous hall signal. This trilayer system can be tuned in-situ to display superconductivity instead of magnetism [3]. We will discuss possible magnetic states, complementary probes to examine which state actually emerges as the ground state in each system, and what one might do with such states.

[1] A.L. Sharpe et al., “Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene”, Science 365, 6453 (2019).
[2] G. Chen et al., “Tunable Correlated Chern Insulator and Ferromagnetism in Trilayer Graphene/Boron Nitride Moire Superlattice”, Nature 579, 56 (2020)
[3] G. Chen et al., “Signatures of tunable superconductivity in a trilayer graphene moiré superlattice”, Nature 572, 215 (2019).

We are going to discuss the physics reach and the experimental challenges
of directional WIMP-like Dark Matter searches, illustrating the concept of the CYGNUS-TPC international collaboration and how the CYGNO effort fits into it.
We are going to present the latest R&D results in the field and discuss future short and long term developments of such techniques, also in the context of solar Neutrinos measurements.

ProtoDUNE-SP is a single-phase liquid argon (LAr) TPC located at CERN’s neutrino platform facility. This detector is a large scale prototype providing, for the first time, a full validation of the use of the membrane tank technology for large dimension cryostats. With more than 2 years of continuous and stable operation, protoDUNE-SP demonstrates the reliability of the LAr TPC technology for the 10-kton fiducial mass detectors for the DUNE experiment. In this talk the design of the prototype will be presented. The TPC and light system detector performances recently published[1] will be also reviewed.

Two of the outstanding open questions in physics are the nature of dark matter and the fundamental nature of neutrinos. DARWIN is a next-generation experiment aiming to reach a dark matter sensitivity limited by the irreducible neutrino backgrounds. The core of the detector will have a 40 ton liquid xenon target operated as a dual-phase time projection chamber. The unprecedented large xenon mass, the exquisitely low radioactive background and the low energy threshold will allow for a diversification of the physics program beyond the search for dark matter particles: DARWIN will be a true low-background, low-threshold astroparticle physics observatory. I will present the status of the project, its science reach, and discuss the main R&D topics.

The CUPID-Mo experiment, currently taking data at the Laboratoire Souterrain de Modane (France), is a demonstrator for CUPID, the next-generation upgrade of the first ton-scale cryogenic 0νββ-search, CUORE. The experiment is searching for 0νββ decay of 100Mo with an array of 20 enriched ~0.2 kg Li2MoO4 crystals. The detectors are operated deep under the Frejus mountain at a depth of 4800 m.w.e. in a dilution refrigerator at ~20 mK. They are complemented by cryogenic Ge light detectors allowing us to distinguish alpha from beta/gamma events by the detection of both heat and scintillation light signals. With a bolometric performance of ~ 7 keV energy resolution (FWHM) at 2615 keV, full alpha-to-beta/gamma separation and excellent radio-purity levels, we operate in the background free regime. For the present analysis, we consider more than one year of data acquired between March 2019 and April 2020. With 2.17 kg x yr of exposure and a high analysis efficiency of ~ 90%, we are able to set a new world leading limit for 0νββ decay of 100Mo. In this seminar, I will present the details of the analysis, the new limit of T1/2 > 1.4 x 1024 yr at 90% c.i. and I will conclude with an outlook on the data taken up to the end of CUPID-Mo operations in July 2020 and further upcoming analyses.

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.

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)

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.

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

After the discovery of the Higgs boson in 2012, the Large Hadron Collider (LHC) at CERN has turned from a discovery machine to a precision machine. The highly boosted events measured by the LHC experiments are, for the first time, providing us a window on the details of the electroweak symmetry breaking mechanism. A crucial condition to maximise the reach of these studies is a profound understanding of the theoretical implications of perturbative Quantum Field Theory, and in particular of Quantum ChromoDynamics (QCD), for the physics of hadronic collisions at the LHC. In this talk, I will provide an account of the opportunities and the challenges that precision physics at the LHC can offer, focusing in particular on the recent developments in our understanding of higher order calculations in perturbative Quantum Field Theory and how they can help us understand the Higgs sector of the Standard Model.