High-energy behaviour of scattering amplitudes in the standard model effective field theory

Our current understanding of the fundamental interactions among the elementary constituents of matter is encapsulated in a theoretical framework called the standard model. Most of its predictions have been experimentally verified, some to a very high degree of accuracy, in a experimental effort which spans a large number of experiments conducted over several decades at different scales. Notwithstanding its amazing success, observations as well as theoretical arguments point to the existence of new physics at higher scales. A consistent and model-independent approach that can be used to systematically study interactions at very short distances, i.e. at high energy, is that of an effective field theory. In this work, I present the study of several scattering processes at very high energy involving the heaviest degrees of freedom of the standard model, i.e. the top quark, the vector bosons W and Z, and the Higgs boson. I employ the framework of the standard model effective field theory, where the standard model is extended to include higher order operators of dimension six which are compatible with the local and global symmetries at dimension four. The main motivation for this work is to explore the possibly increased sensitivity to new physics of 2 to N scattering amplitudes with respect to 2 to 2 processes which have been already considered. The analysis is divided in two parts. In the first more theoretical part, the high-energy behaviour of the helicity amplitudes is evaluated for every core process, looking for footprints of S-matrix unitarity violation. In the second more phenomenological part, core processes are embedded in realistic initial-final states that can appear at future very high-energy lepton collider. This allows to estimate their sensitivity to a selected set of the standard model effective field theory operators and determine whether they can be useful to improve on the current (or expected) constraints on the corresponding Wilson coefficients

Buchi neri e singolarita in relatività generale

In questo lavoro di tesi triennale si vanno a studiare le soluzioni di Schwarzschild e Kerr per le equazioni di Einstein nel vuoto nell'ambito della Teoria della Relatività Generale. In particolare si esaminano in maniera critica i concetti di buco nero e di singolarità dello spazio-tempo che emergono nel corso di tale studio. Il "Capitolo 1" è focalizzato sullo studio della soluzione di Schwarzschild, la prima ad essere stata trovata storicamente alle equazioni di Einstein. A partire dall'analisi classica del moto geodetico di corpi di prova si introducono in maniera qualitativa i concetti di orizzonte degli eventi e di buco nero, esaminando mediante diagrammi conformi la causalità nella soluzione di Schwarzschild. Il "Capitolo 2" è centrato sull'esposizione del concetto di buco nero e di singolarità nello spazio-tempo. In seguito ad aver visto come cambia la struttura causale nell'ambito della Relatività Generale, si procede alla ricerca di una definizione soddisfacente del concetto di singolarità di uno spazio-tempo e delle condizioni affinché essa esista: tale ricerca termina con l'enunciazione dei teoremi sulle singolarità di Penrose e Hawking. Si conclude il capitolo con l'introduzione formale della nozione di buco nero, studiando poi in maniera molto qualitativa il collasso gravitazionale che dà origine ai buchi neri ed i possibili modi per rilevarne la presenza. Il "Capitolo 3" infine tratta la meccanica di un buco nero rotante di Kerr alla luce dei concetti visti nei due capitoli precedenti. Dall'analisi delle proprietà geometriche di tale soluzione si ricordano i risultati principali per il moto geodetico di corpi di prova e ci si sofferma, in particolare, sul processo di Penrose che in linea teorica permette l'estrazione di energia da buchi neri rotanti e sullo studio delle singolarità della metrica della soluzione mediante diagrammi conformi

Vector boson fusion at multi-TeV muon colliders

High-energy lepton colliders with a centre-of-mass energy in the multi-TeV range are currently considered among the most challenging and far-reaching future accelerator projects. Studies performed so far have mostly focused on the reach for new phenomena in lepton-antilepton annihilation channels. In this work we observe that starting from collider energies of a few TeV, electroweak (EW) vector boson fusion/scattering (VBF) at lepton colliders becomes the dominant production mode for all Standard Model processes relevant to studying the EW sector. In many cases we find that this also holds for new physics. We quantify the size and the growth of VBF cross sections with collider energy for a number of SM and new physics processes. By considering luminosity scenarios achievable at a muon collider, we conclude that such a machine would effectively be a "high-luminosity weak boson collider," and subsequently offer a wide range of opportunities to precisely measure EW and Higgs coupling as well as to discover new particles.Comment: 58 pages, 17 figures, 9 tables. A contribution to Snowmass 202

Probing Ensemble Properties of Vortex-avalanche Pulsar Glitches with a Stochastic Gravitational-Wave Background Search

A stochastic gravitational-wave background (SGWB) is expected to be produced by the superposition of individually undetectable, unresolved gravitational-wave (GW) signals from cosmological and astrophysical sources. Such a signal can be searched with dedicated techniques using the data acquired by a network of ground-based GW detectors. In this work, we consider the astrophysical SGWB resulting from pulsar glitches, which are sudden increases in the rotational pulsar frequency, within our Galaxy. More specifically, we assume glitches to be associated with quantized, superfluid, vortex-avalanches in the pulsars, and we model the SGWB from the superposition of GW bursts emitted during the glitching phase. We perform a cross-correlation search for this SGWB-like signal employing the data from the first three observation runs of Advanced LIGO and Virgo. Not having found any evidence for a SGWB signal, we set upper limits on the dimensionless energy density parameter $\Omega_{\mathrm{gw}}(f)$ for two different power-law SGWBs, corresponding to two different glitch regimes. We obtain $\Omega_{\mathrm{gw}}(f)\leq 7.5 \times 10^{-10}$ at 25 Hz for a spectral index 5/2, and $\Omega_{\mathrm{gw}}(f)\leq 5.7 \times 10^{-17}$ at 25 Hz for a spectral index 17/2. We then use these results to set constraints on the average glitch duration and the average radial motion of the vortices during the glitches for the population of the glitching Galactic pulsars, as a function of the Galactic glitch rate.Comment: 16 pages, 3 figures, 1 tabl

pygwb: Python-based library for gravitational-wave background searches

The collection of gravitational waves (GWs) that are either too weak or too numerous to be individually resolved is commonly referred to as the gravitational-wave background (GWB). A confident detection and model-driven characterization of such a signal will provide invaluable information about the evolution of the Universe and the population of GW sources within it. We present a new, user-friendly Python--based package for gravitational-wave data analysis to search for an isotropic GWB in ground--based interferometer data. We employ cross-correlation spectra of GW detector pairs to construct an optimal estimator of the Gaussian and isotropic GWB, and Bayesian parameter estimation to constrain GWB models. The modularity and clarity of the code allow for both a shallow learning curve and flexibility in adjusting the analysis to one's own needs. We describe the individual modules which make up {\tt pygwb}, following the traditional steps of stochastic analyses carried out within the LIGO, Virgo, and KAGRA Collaboration. We then describe the built-in pipeline which combines the different modules and validate it with both mock data and real GW data from the O3 Advanced LIGO and Virgo observing run. We successfully recover all mock data injections and reproduce published results.Comment: 32 pages, 14 figure

Constraints on planetary and asteroid-mass primordial black holes from continuous gravitational-wave searches

We present new constraints on the merging rates of planetary-mass and asteroid-mass primordial black hole binaries using limits on continuous waves (quasimonochromatic, quasi-infinite duration signals) derived from an all-sky search for isolated compact objects in the first six months of the third observing run (O3a) of LIGO/Virgo. We calculate the merging rates of these binaries in a model-independent way, and convert them to constraints on the primordial black hole abundance with minimal modeling assumptions. Our results show that all-sky searches are sensitive to sources at most O(10 pc) away for systems with chirp masses of O(10-5 M⊙) at gravitational-wave frequencies around 30 Hz-40 Hz. These results also show that continuous-wave searches could in the future directly probe the existence of planetary-mass and asteroid-mass primordial black holes, especially those in binaries with asymmetric mass ratios. Furthermore, they demonstrate that new methods accounting for the full nonlinear gravitational-wave frequency evolution are needed to improve constraints on primordial black holes.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Probing planetary-mass primordial black holes with continuous gravitational waves

Gravitational waves can probe the existence of planetary-mass primordial black holes. Considering a mass range of [10−7−10−2]M⊙, inspiraling primordial black holes could emit either continuous gravitational waves, quasi-monochromatic signals that last for many years, or transient continuous waves, signals whose frequency evolution follows a power law and last for O(hours-months). We show that primordial black hole binaries in our galaxy may produce detectable gravitational waves for different mass functions and formation mechanisms. In order to detect these inspirals, we adapt methods originally designed to search for gravitational waves from asymmetrically rotating neutron stars. The first method, the Frequency-Hough, exploits the continuous, quasi-monochromatic nature of inspiraling black holes that are sufficiently light and far apart such that their orbital frequencies can be approximated as linear with a small spin-up. The second method, the Generalized Frequency-Hough, drops the assumption of linearity and allows the signal frequency to follow a power-law evolution. We explore the parameter space to which each method is sensitive, derive a theoretical sensitivity estimate, determine optimal search parameters and calculate the computational cost of all-sky and directed searches. We forecast limits on the abundance of primordial black holes within our galaxy, showing that we can constrain the fraction of dark matter that primordial black holes compose, fPBH, to be fPBH≲1 for chirp masses between [4×10−5−10−3]M⊙ for current detectors. For the Einstein Telescope, we expect the constraints to improve to fPBH≲10−2 for chirp masses between [10−4−10−3]M⊙.SCOPUS: ar.jinfo:eu-repo/semantics/publishe