Scientific Series

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

Over the last decade, the Effective Field Theory of Large Scale Structure (EFTofLSS) has emerged as a frontrunner in the effort to produce accurate models of cosmological statistics. Quantities such as power spectra can be fit with sub-percent precision, and there is a wealth of literature applying the formalism to more complex statistics. It is interesting to ask what lies ahead for the theory. Can it be used for cosmological parameter inference? And is it just for statistics based on the 3D density field?

In this talk, I will present a pedagogical introduction to the EFTofLSS, discussing its motivation and basic formalism, as well as a few of its theoretical challenges. To demonstrate the utility of the theory beyond the blackboard, I will discuss the analysis of galaxy power spectra. Using this model, competitive constraints can be placed on cosmology utilizing all the large-scale spatial information, not just the position of the Baryon Acoustic Oscillations. In particular, this yields the strongest CMB-independent measurement of H0. 

In answering the second question, I will introduce two less conventional applications of the EFTofLSS. Firstly, the marked density field. This is simply the matter field weighted by its local overdensity, and recent works have shown its power spectrum to be capable of placing strong constraints on the neutrino mass. I will discussing its perturbative modeling, highlighting its unusual features, and how the model allows us to shed light on the surprising constraining of the statistic. An additional statistic of interest is weak lensing. Creating an analytic model for this has its own complications, since it is sensitive to a large range of scales, requiring extensions to the usual EFTofLSS modeling. Crucial to this effort is the development of a matter power spectrum model which is accurate on all scales; I will present the results of recent modeling efforts within the ‘Effective Halo Model’, and discuss future applications to integrated statistics such as weak lensing.

Zoom Link: https://pitp.zoom.us/j/91697113596?pwd=OTh3ZjZ5SHd5Q09sTFdReUMyb0hpUT09

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.

The study of compact objects in the strong field regime needs a thorough understanding of the initial value problem in general relativity at the resence of hydrodynamical or magnetohydrodynamical sources. This is a twofold problem that includes general relativistic solutions that represent realistic astrophysical systems at a given moment in time as well as their subsequent evolutions. In this talk I will present the fundamental principles of this endeavor as well as efforts in understanding a great variety of astrophysical systems from binary neutron stars to ergostars and black hole-disks through numerical relativity.

Neutrinos are a key (although implicit) ingredient of the standard cosmological model, LambdaCDM. Firstly, neutrinos directly participate in neutron freeze out during BBN, and secondly, they represent 40% of the energy density of the Universe after electron positron annihilation up to almost matter radiation equality. The latter fact makes neutrinos a necessary element to understand CMB observations. 

In this talk, I will review the cosmological implications of neutrinos. I will explain how current cosmological observations can be used to constrain their masses, their abundances, and their properties -- such as their interaction rate with other species. In particular, I will highlight that the typically very stringent constraint on their masses can be substantially relaxed if neutrinos decay on cosmological timescales. I will illustrate the implications of neutrino decays in cosmology with a few well-motivated neutrino mass models in which neutrinos can decay. I will then show that Planck CMB observations are a powerful tool to constraint neutrino interactions with neutrinophilic bosons. In particular, I will demonstrate that Planck legacy constraints neutrinophilic bosons with couplings as small as 10^{-13} with neutrinos for boson masses in the 0.1 eV < m < 300 eV range. I will finish by reviewing the role neutrinos can play with regards to the outstanding Hubble tension. I will show that pseudogoldstone bosons (majorons) interacting with neutrinos right before recombination represent a well motivated possibility to ameliorate (and potentially solve) the Hubble tension.

Neural networks (NNs) normally do not allow any insight into the reasoning behind their predictions. We demonstrate how influence functions can unravel the black box of NN when trained to predict the phases of the one-dimensional extended spinless Fermi-Hubbard model at half-filling. Results provide strong evidence that the NN correctly learns an order parameter describing the quantum transition. Moreover, we demonstrate that influence functions not only allow to check that the network, trained to recognize known quantum phases, can predict new unknown ones but even guide physicists in understanding patterns responsible for the phase transition. This method requires no a priori knowledge on the order parameter, the system itself, or even the architecture of the ML model.

The Fermi Gamma-ray Space Telescope has provided unique insights into the Universe's biggest explosions over the past 12 years. With thousands of gamma-ray bursts (GRBs) detected by the Gamma-ray Burst Monitor (GBM) and hundreds by the Large Area Telescope (LAT), we have learned about the broad properties of the populations of these events and got unique insights into their emission mechanisms, environment, and physical properties. In this seminar, I'll review highlights of GRB science from the Fermi mission at low (keV) and high (GeV) energy, as well as the recent discovery of very-high (TeV) energy emission from GRB 180720B and GRB 140114C observed by the Cherenkov Telescopes of the H.E.S.S. and MAGIC experiments, respectively

The velocity of a gravitational wave (GW) source provides crucial information about its formation and evolution processes.

Previous studies considered the Doppler effect on the phase of GWs as a potential signature of a time-dependent velocity of the source. However, the Doppler shift only accounts for the time component of the wave vector, and in principle motion also affects the spatial components. In my talk I discuss the latter effect, known as “aberration” for light, for GWs and how it affects the waveform modeling of an accelerating source. I show that the additional aberrational phase shift could be detectable in two astrophysical scenarios, namely, a recoiling binary black hole (BBH) due to GW radiation and a BBH in a triple system.

Further, I discuss how adding the aberrational phase shift in the waveform templates could significantly enhance the detectability of moving sources.

Given a vector in a representation, can it be distinguished from zero by an invariant polynomial? This classical question in invariant theory relates to a diverse set of problems in mathematics and computer science. In quantum information, it captures the quantum marginal problem and recent bounds on tensor ranks. We will see that the general question can be usefully thought of as an optimization problem and discuss how this perspective leads to efficient algorithms for solving it.