Stochastic effects in ultra slow-roll inflation

Longo, Mirko (2018) Stochastic effects in ultra slow-roll inflation. [Laurea magistrale], Università di Bologna, Corso di Studio in Fisica [LM-DM270]
Documenti full-text disponibili:
[img] Documento PDF (Thesis)
Disponibile con Licenza: Salvo eventuali più ampie autorizzazioni dell'autore, la tesi può essere liberamente consultata e può essere effettuato il salvataggio e la stampa di una copia per fini strettamente personali di studio, di ricerca e di insegnamento, con espresso divieto di qualunque utilizzo direttamente o indirettamente commerciale. Ogni altro diritto sul materiale è riservato

Download (1MB)


In this work we apply the stochastic inflation formalism to backgrounds that deviate from standard slow-roll in a way that can lead to the production of primordial black holes. We analyse the effects of sudden transitions on the stochastic noise amplitude and its potential impact on the production of primordial black holes in single field inflation. We justify the claim that primordial black holes can be responsible for a significant fraction of the dark matter abundance today and estimate the required enhancement in the power spectrum. We introduce the Hamiltonian formalism and the coarse-graining of the quantum field and its momentum, allowing us to obtain a quantitative measure of the role of quantum diffusion in the production of primordial black holes. We mainly focus our analysis on a Starobinsky potential given that it is rich enough to allow for the dynamics of the scalar field during inflation to include an ultra slow-roll phase induced by a transition from a relatively large slow-roll parameter to a hierarchically smaller one. This has the effect of making the field perturbations undergo sudden transitions and rise from its ground state to an excited state. We present two procedures that we employed when calculating the power spectrum: a numerical and an analytical one. Both methods show that stochastic effects are negligible at small scales where their amplitude is time dependent and vanishes at late times, and that for scales leaving the horizon after the ultra slow-roll phase the de Sitter estimate of $H^2/(4\pi^2)$ is approximately correct. We therefore demonstrate that the estimates in the literature are incomplete and that a revaluation of the role of stochastic effects on primordial black hole production is in order.

Tipologia del documento
Tesi di laurea (Laurea magistrale)
Autore della tesi
Longo, Mirko
Relatore della tesi
Corso di studio
Curriculum A: Teorico generale
Ordinamento Cds
Parole chiave
stochastic,inflation,primordial black hole,PBH,cosmology,starobinsky,power spectrum,enhancement,quantum diffusion,slow roll,ultra slow roll,dark matter,curvature perturbations
Data di discussione della Tesi
14 Dicembre 2018

Altri metadati

Statistica sui download

Gestione del documento: Visualizza il documento