My paper with Marco Calzà, Francesco Gianesello, and Max Rinaldi, where we study the stochastic gravitational wave background signal resulting from inspiraling cosmologically coupled BHs (see this earlier news item), has now officially been published in Scientific Reports (making this my third proper Nature publication)! The full bibliographic coordinates for the paper are Sci. Rep. 14 (2024) 31296. Here is the link to the paper (which is published Open Access).
Stochastic gravitational wave background from cosmologically coupled black holes paper accepted in Scientific Reports!
My paper with Marco Calzà, Francesco Gianesello, and Max Rinaldi (proudly 100% made within the Theoretical Gravitation and Cosmology Group led by myself and Max!) , where we study the stochastic gravitational wave background signal resulting from inspiraling cosmologically coupled BHs (see this earlier news item), has been accepted for publication in Scientific Reports, part of the Nature Portfolio collection of journals (therefore making this my third proper Nature publication)! With respect to the earlier version we have slightly changed the title and explained the content of Fig. 2 much more clearly, but the main message of the paper is otherwise unchanged. You can read the preprint version of the paper on arXiv: 2409.01801.
Visit by Davide Racco and Flaminia Giacomini
For the next days we have the pleasure of hosting Davide Racco and Flaminia Giacomini, who are visiting us from Zurich (respectively from the University of Zurich+ETH, and ETH). Both are very well-known researchers with interests at the intersection of particle physics and cosmology (Davide) and at the interface between quantum theory/quantum information and gravity (Flaminia). They will be giving seminars by the titles of “Insights on fundamental physics from Gravitational Wave backgrounds” and “Quantum effects in gravity from a delocalised quantum source” . Welcome Davide and Flaminia!
Stochastic gravitational wave background from cosmologically coupled black holes
Very happy to see my latest paper with Marco Calzà, Francesco Gianesello, and Max Rinaldi out! This is a 100% “made in Trentino” paper, and more precisely made within the Theoretical Gravitation and Cosmology Group led by myself and Max. At some point in 2023, the possibility that dark energy could be sourced by cosmologically coupled black holes (BHs), whose mass increases in time through purely cosmological growth even in the absence of accretion and merger events, received a lot of interest, especially given the possibility that signatures of such a coupling could have been observed in the growth of supermassive BHs in red-sequence elliptical galaxies. In today’s paper we show that mergers of such cosmologically coupled BHs would lead to a stochastic gravitational wave background whose strength is significantly larger (up to an order of magnitude stronger!) than the standard one from mergers of uncoupled BHs, with very interesting implications for the signal observed last year by pulsar timing arrays (among which NANOGrav, EPTA, PPTA, and CPTA), which is a bit too strong to be easily explainable by mergers of standard BHs. You can read our results in the preprint we just posted on arXiv: 2409.01801.
Giovanni Piccoli's MSc defense
Congratulations to Giovanni Piccoli, who today successfully defended his MSc thesis, by the title of “The very small-scale primordial Universe: complementary tests from Cosmic Neutrinos and Gravitational Waves” (with the opponent being Prof. Alessandro Roggero)! Giovanni’s defense was simply outstanding, and he received top grades and honours, i.e. 110 e Lode. In his thesis which I supervised, Giovanni developed complementary tests of the small-scale power spectrum of primordial fluctuations using the stochastic gravitational wave background measured by pulsar timing arrays, and forecasting the reach in this sense of a potential future measurement of the cosmic neutrino background (CNB) from laboratory experiments. What does the CNB have to do with the small-scale power spectrum? We’re writing up a paper based on Giovanni’s results, and I can guarantee it will be extremely exciting, so no spoilers!
Scale-invariant inflation meets cosmological data
Very happy to see my latest preprint with Chiara Cecchini, Mariaveronica De Angelis, William Giarè, and Max Rinaldi finally out on the arXiv - kudos especially to the three younger collaborators (Chiara, Mariaveronica, and William) who did all the heavy-lifting! We studied a theoretically very well-motivated classically scale-invariant inflationary model, quadratic in curvature and featuring a scalar field non-minimally coupled to gravity, where inflation occurs in the transition between two de Sitter regimes, during which dynamical breaking of scale-invariance occurs and the Planck mass emerges. We show that the model is in excellent agreement with current CMB data, and that it makes a highly testable prediction for the amplitude of primordial tensor modes: r≳0.003. Given its very specific predictions, near-future CMB experiments can therefore make or break scale-invariant inflation - we argued that this, in combination with its strong theoretical motivation, makes the model an interesting benchmark to add when studying future tests of inflation from CMB data. You can read our results in the preprint we just posted on arXiv: 2403.04316.
Inflationary gravitational waves and PTA paper published in JHEAp!
My single-author paper studying an inflationary interpretation of the signal observed by PTA experiments, which I previously reported on in an earlier news item, has now officially been published in JHEAp! The full bibliographic coordinates for the paper are JHEAp 39 (2023) 81. Here is the link to the paper (which is published Open Access).
Tonale Winter School registration open
Registration for the 2023 Tonale Winter School on Cosmology, where I will be lecturing, is now open. Besides cosmological tensions, the other topics covered this year are stochastic gravitational waves backgrounds, full-sky surveys, and the effective field theory of structure formation. Please see the official school page for further details. Only a maximum of 40 participants will be accepted and, given the large number of applications usually received, it is strongly recommended to register as soon as possible. Note that I am not involved in the selection process, so please reach out to the organizers if you have any questions.
Inflationary gravitational waves and PTA paper accepted in JHEAp!
My single-author paper where I examine an inflationary interpretation of the signal observed by PTA experiments (see this earlier news item) has been accepted for publication in JHEAp! For once, after papers which went through extremely long journeys, this was a very quick turnaround, as the referee report clearly highlighted the timeliness and importance of the results. You can read the preprint version of the paper on arXiv: 2306.16912.
Inflationary gravitational waves and the pulsar timing array signal
Yesterday was a really exciting and breakthrough day for physics, as four major Pulsar Timing Array (PTA) experiments (NANOGrav, EPTA, PPTA, and CPTA) reported evidence for a stochastic gravitational wave background (SGWB) signal in the nHz range, for which one of the most likely explanations is that of merging supermassive black hole binaries. Today I posted a new single-author paper, where I examine whether the signal could instead have been produced during inflation. The answer is “potentially yes”, although the underlying inflationary model would have to be rather strange, requiring a very blue tilt (~1.8, not something you can get in single-field slow-roll inflation) and a very low reheating scale (at most ~10 GeV). As an aside, I’ve also explicitly written down a bivariate Gaussian approximation to the joint amplitude-tilt posterior for the NANOGrav results, which can come in handy if you want to perform a similar analysis for other models. You can read my results in the preprint I just posted on arXiv (the first since September 2022 - it’s obvious that teaching has come in between 😄): 2306.16912.
