Journal Club

 

 

Journal Club Seminari 2022


   
 
18-02-2022   (AULA C - Via della Vasca Navale n. 84)
Chair:
ore 14:00 Federico Manzoni
(DOTTORATO IN FISICA)
Asymptotic symmetries in Maxwell and Einstein theories

In 1962 Bondi, van de Burg, Metzner and Sachs discovered that asymptotically flat spacetimes possess an asymptotic symmetries group much larger than the Poincarè group. Since then, the interest in the study of asymptotic symmetries has been growing, leading today to a possible extension of the AdS/CFT correspondence to asymptotically
flat spacetimes. We discuss asymptotic symmetries in Maxwell and linearized Einstein theories, calculating the asymptotic charges in the first case and the asymptotic killing vectors in the second one.

 
ore 15:00 Alessandro Brin
(DOTTORATO IN FISICA)
Bright basal reflections beneath SPLD: new laboratory tests on terrestrial analogues

Bright basal reflections detected at the base of the south polar layered deposits (SPLD) on Mars by MARSIS instrument (a low-frequency radar on the Mars Express spacecraft) have been interpreted as evidence of wet sediments or briny ponded water. Owing to the low temperature values expected at the base of the SPLD however, the presence of briny water has been questioned with alternative materials, such as clay, hydrated salts, and saline ices proposed as the source of the bright reflections. In this discussion I will briefly discuss all these different scenarios, illustrating new laboratory tests on terrestrial analogues.
 
 
07-04-2022   (AULA C - piano terra- V. della Vasca Navale n. 84)
Chair:
ore 14:15 Vittoria Elvezia Gianolli
(DOTTORATO IN FISICA)
X-ray absorption properties in a type 1 quasar sample from the SDSS survey

Generally, optical and X-ray studies support the Unified Model, which was proposed in order to explain the variety of classes and sub-classes in which Active Galactic Nuclei (AGN) have been dived. According to it, AGNs present similar inner regions and are powered by the same central engine. While the phenomenological differences arise from geometrical effects associated with an optically-thick obscuring torus that surrounds the nuclear engine, and the relative position of the observer.
Despite the fact that the majority of AGNs classified as type 1 are unabsorbed and Type 2 AGNs are usually absorbed, the number of cases in which observations show disagreement between X-ray and optical classifications has increased.
In this context, we study a sample of optically classified as Type 1 quasars (QSO) that are obscured in the X-ray band. The main aims are to estimate the rate of QSO with obscured X-ray spectra and to investigate the physical origin of the discordant optical/X-ray properties.
 
ore 15:00 Silvia Tosi
(DOTTORATO IN FISICA)
Characterization of evolved stars

During the AGB lifetime the stars eject into the surrounding environment gas, which on the chemical side is significantly altered with respect to the initial chemistry, and dust, formed in the cool and expanded circumstellar envelopes. Determining the mineralogy and the amount of dust is fundamental to establish their role as pollutants of the interstellar medium, and therefore the way in which they participate in the life cycle of the host galaxy. This is made difficult by the poor knowledge of some physical mechanisms however a valuable approach to infer information on the evolution of AGB stars is offered by the study of post-AGB stars. Indeed, main aspects of the evolution of these stars are well known, and the spectra of the latter sources can be more easily analyzed to derive the chemical composition and to characterize the dust in their surroundings. For this purpose, we have analyzed 10 post-AGB candidates from the LMC and the SMC. 


 
 
10-06-2022   (AULA A (primo piano - Via Della vasca Navale n. 84))
Chair:
ore 14:00 Giulia Degni
(DOTTORATO IN FISICA)
Cosmic Voids and their surroundings: a new cosmological probe

Abstract Journal Club  Giulia Degni
June 2022
Since the discovery of the expansion of the Universe, one of the main problems in physics relies on the investigation of the nature of dark energy and the exploration of alternative theories of gravity. According to the standard model in Cosmology, the CDM, almost 95% of our Universe, the dark components, is unknown, it is fundamental to develop new techniques to study and analyze the Universe. A powerful tool is given us from the observation of the Large Scale Structure of the Universe. Modern surveys are able to provide a huge amount of data and it is possible to develop detailed maps of the observable Universe tracing the distribution of galaxies. Inside these maps it is possible to identify
the different kind of structure which the Universe is made up: galaxy clusters (highest density regions), filaments (high density regions connecting galaxyclusters) and cosmic voids (lowest density regions). Recently, cosmic voids have proven to be powerful cosmological probes to study the nature of the accelerated expansion of the Universe by putting constraints on cosmological parameters.
The importance of cosmic voids, large empty underdense regions in space, relies mainly on their shape: on average, voids are intrinsically spherically symmetric and, once rescaled by their size, possess a universal density profile. From an observational perspective, voids are identified from spectroscopic galaxy redshift surveys, i.e., from the spatial distribution of galaxies whose observedredshifts
are used to infer distances. As a result, the observed shape of the voids is
not spherical but distorted by two effects. The first one derives from assuming an incorrect cosmological model. The second one originates from ignoring the Doppler due to the proper motion of the galaxy that, on top of the recession velocity, contributes to the observed redshift. Therefore, is it possible to use cosmic voids to extract cosmological information and constrain the nature ofthe dark components.
 
ore 14:45 Ivano Saccheo
(DOTTORATO IN FISICA)
Mean SED of hyper-luminous QSOs

-Mean SED of hyper-luminous QSOs-
The study of AGN SED provides both a direct description of the physical processes responsible
for the emission in different bands and a comprehensive picture of sources energy budgets. In this talk, I will present the characterization of the mean SED of a sample composed of the most luminous type 1 QSOs (the WISSH sample, Lbol>1047 erg/s at z~2-4.5, focusing on the differences
we find with respect to the typical SED of less luminous sources. I will also present the mean SED derived from different sub-samples of QSOs showing peculiar spectral features (BAL vs non-
BAL QSO and CIV weak vs non CIV weak QSOs) and the bolometric corrections obtained for 5100 Å and 3 μm luminosities.
By extending this analysis to the more heterogeneous SDSS QSO catalog, I will discuss whether our results can be generalized to the entire population of hyper-luminous QSOs. Finally, I will
discuss the location of WISSH QSOs in the recently proposed star-forming vs AGN dominated galaxy diagnostic diagram (Symeonidis & Page 2021) and its possible extension up to z = 4.5.
 
21-10-2022   (Aula F- primo piano - Via della Vasca Navale n. 84)
Chair:
ore 00:02 Federico Montereali
(DOTTORATO IN FISICA)
Search for Higgs boson pair production in the two bottom quarks plus two photons final state in proton-proton collisions at LHC with the ATLAS detector

The Higgs boson self-coupling provides information about the structure of the Higgs potential and the self-coupling of the Higgs boson can be directly probed by studying Higgs boson pair (HH) production, that is an extremely rare process (non yet observed). At LHC, HH is mainly produced via gluon-gluon Fusion (ggF) and Vector-Boson Fusion (VBF) modes, that are affected by the trilinear self-interaction vertex. A deviation from the SM predicted self-coupling value may point to physics Beyond the Standard Model (BSM).
The search for Higgs boson pair production in the final state with two bottom quarks and two photons in proton-proton collisions at LHC, with data collected by the ATLAS detector and corresponding to an integrated luminosity of 139 fb$^{-1}$ will be presented. This final state is characterized by a small branching ratio (0.26%), but also by a clear experimental signature, thanks to the excellent di-photon invariant mass resolution, which makes it one of the "golden channels" for the HH searches.
The analysis strategies with possible techniques for improving sensitivity, and the recent results are discussed.
ore 12:45 Rita Antonietti
(DOTTORATO IN FISICA)
Directional dark matter searches with CYGNO experiment -

The CYGNO experiment aims to exploit the optical readout approach of multiple Gas Electron Multipliers
(GEM) structures in large volume TPCs for the study of rare events as interaction of low-mass (few GeV)
Dark Matter (DM) or solar neutrinos. The TPC volume is filled with an He:CF4 gas mixture at atmospheric
pressure. The photons produced in the multiplication process are read out by sCMOS sensors, which
guarantees a high read granularity, a high sensitivity and a low noise level. The drift time of ionization is
measured by PMTs in order to obtain the coordinate perpendicular to the camera plane. The combined use
of high-granularity sCMOS cameras and fast light sensors allows the reconstruction of the 3D direction of
the tracks, offering good energy resolution and very high sensitivity in the few keV energy range. A detector
sensitive to the incoming particle direction, in case of DM discovery, will be important in order to study its
properties. The CYGNO experiment goal is to build and to operate a 1m3 demonstrator underground at the
Gran Sasso National Laboratories (LNGS) aiming at a larger scale apparatus ({30 m^3−−100 m^3) at a later
stage
 
28-10-2022   (aula C )
Chair:
ore 15:00 Leonardo Perin
(DOTTORATO IN FISICA)
Molecular Dynamics Simulations Of Supercooled Aqueous Solutions -

Molecular dynamics are a powerful tool for the study of the properties of systems by analyzing the physical movements of the atoms. The trajectories of atoms are determined by numerically solving the equation of motion given the interatomic potential, and from these trajectories thermodynamic, dynamic and structural properties are determined. Here we present a molecular dynamics simulation study of a supercooled LiCl aqueous solution. The purpose is to study how the anomalous behavior of water changes in the presence of the solute, in particular the temperature of maximum density (TMD) line and the liquid-liquid critical point (LLCP) are examined. Structural properties are also examined through the study of the radial distribution functions
ore 15:45 Matteo Romoli
(DOTTORATO IN FISICA)
Double copy correspondence: a relation between gravity and gauge theories

The double copy correspondence provides a novel perspective on the relation between gravity and gauge theories. In simple terms, it is based on the idea that gravity can be written as a sort of square of two Yang-Mills gauge theories. This was first proposed in the context of amplitudes for which, at tree level, the correspondence is a proved theorem and it is also really promising when dealing with loops corrections. The Lagrangian formulation is not yet as well studied, even if some progress has been made in the last years. In this context, I am exploring the possibility for a double copy correspondence for asymptotic symmetries.
ore 16:30 Simone Marciano
(DOTTORATO IN FISICA)
Leptogenesis From U(1) Flavour Symmetry

We present a simple extension of the Standard Model with three right-handed neutrinos in a SUSY framework, with an additional U(1)F abelian flavor symmetry with a non standard leptonic charge Le −Lμ −Lτ for lepton doublets and arbitrary right-handed charges. The model is able to reproduce the experimental values of the mixing angles of the PMNS matrix and of the r = Δm2sun/Δm2atm ratio, with only a moderate fine tuning of the Lagrangian free parameters. The baryon asymmetry of the Universe is generated via thermal leptogenesis through CP-violating decays of the heavy right- handed neutrinos. We present a detailed numerical solution of the relevant Boltzmann Equations (BE

Copyright© 2014 Dipartimento di Matematica e Fisica