I’m truly thrilled to see my latest preprint with my PhD student Davide Pedrotti, which also happens to be Davide’s first paper, out on arXiv! This work is the one I was anticipating in an earlier news item, and is based on part of Davide’s MSc thesis - so, needless to say, kudos to Davide who did all the hard work! There is a well-known correspondence between black hole quasinormal modes (QNMs) in the eikonal limit (ℓ>>1), and the size of BH shadows: this correspondence has been extensively studied for spherically symmetric space-times, but the extension to rotating space-times is non-trivial, and has only been worked out either only for equatorial QNMs (m=±ℓ), or for general QNMs but limited to the Kerr metric. What we did with Davide was to extend this correspondence to more general rotating space-times, then testing it explicitly on the rotating regular Bardeen and Hayward BHs, while also discussing the conditions under which the correspondence holds within general rotating space-times (basically the Hamilton-Jacobi and Klein-Gordon equations have to be separable). You can read our results in the preprint we just posted on arXiv (with what I think is a pretty cool title): 2404.07589.
Visit to Zurich
Today and tomorrow I am visiting the beautiful city of Zurich. I was invited by Jaiyul Yoo to give a seminar (“Seven hints that early-time new physics alone is not sufficient to solve the Hubble tension”, slides here) at the Department of Astrophysics of the University of Zurich, and I will also be paying a quick visit to ETH, mostly to catch up with my former student Alex Reeves. It has been a very interesting and productive visit so far, and I learned a lot about what one could call using the umbrella term of “relativistic effects” in galaxy surveys, the study of which is something where Jaiyul’s group is probably one of the leading groups in the world. Non-scientific highlights included a fantastic Spanish dinner, and a very enjoyable drive through the Alps!
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!
Visit by Marc Schneider
We’re excited to welcome our latest visitor: Marc Schneider from SISSA! Marc is currently a postdoc at SISSA, where he has been doing a lot of interesting work especially on the possibility that singularities in GR may be somewhat tamed once quantum effects are taken into account, at which point fields and stress-energy tensor should be treated more as distributions than functions. Marc will be delivering a seminar at TIFPA by the title of “Probing the Big Bang with Quantum Fields”. He already delivered a very interesting talk on the subject at the XXV SIGRAV conference, and I look forward to hearing more and discussing these ideas in a more informal setting. Welcome Marc!
Jun-Qian Jiang joins my group!
I’m very happy to welcome my latest group member, Jun-Qian Jiang (江俊钱)! Jun-Qian is currently a PhD student at the University of Chinese Academy of Sciences under the supervision of Prof. Yun-Song Piao, and has been doing a lot of interesting and very diversified work in the fields of cosmological tensions, inflation, gravitational waves, and so on. He joins my group for the next 6 months as a long-term visiting PhD student. We still have to figure out what we will be working on, but it likely will have to do with cosmological tensions and possibly implications for inflation. Welcome Jun-Qian, and I hope you will enjoy your stay in Italy!
Journal club/group meetings restart
This afternoon we restarted the journal club tradition for the Theoretical Gravitation and Cosmology group, which basically plays the role of our informal group meetings. Between faculty, visiting faculty, postdocs, PhD students, and MSc students, it was great to see 19 of us in the room (with a couple more yet to join us)! After a quick round of presentations, Max, Chiara, and I presented our scale-invariant inflation paper. One of my next tasks will be to update the group’s website, which is chronically out-of-date. And hopefully I’ll be able to post a group picture soon, once everybody has joined us!
Simony Santos da Costa joins our group!
We’re really happy to welcome Simony Santos da Costa as the second postdoc in our group! Simony will be here for the next two years on a prestigious Caritro Fellowship, and will be working with myself and Max Rinaldi on tests of inflation and dark sector physics through the latest cosmological data, while also developing an ambitious outreach program at MUSE. Simony was last a postdoc at INFN Pisa, where she held one of the prestigious INFN theory fellowships for foreigners (or Italians who have been abroad for long enough). Fun fact: Simony will be sharing an office with Marco Calzà, and they both speak Portuguese (and Italian)! Welcome to our group Simony, and I’m really looking forward to working on many exciting projects together!
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.
Leonardo Comini joins my group!
More members joining my group (and more to come soon)! Today Leonardo Comini has officially begun his Master’s thesis work under my supervision, where he will be studying what a particular class of early JWST observations have to say about ΛCDM. Welcome Leonardo, looking forward to our work together!
Teaching restarts today
Today my teaching duties restart once more - this semester I’ll only be teaching Classical Thermodynamics for the Mathematics BSc. Last year’s course was very successful, and I hope to be able to replicate the success this year. Since I will be teaching mathematicians, for today’s first lecture I decided to set the record straight and openly admit that, yes, we physicists do simplify differentials and treat them as fractions. Hopefully this helped break the ice! Once more, all my teaching material will be made publicly available, while being regularly updated, on the English and Italian versions of my teaching page.
PhD Programme Executive Committee
I’m extremely pleased to have been nominated member of the new Executive Committee of our PhD School (Comitato Esecutivo del Corso di Dottorato). The other members of the committee will be Raffaello Potestio (coordinator of the PhD school and chair of the committee), Gabriele Ferrari (deputy coordinator of the PhD school), Matteo Calandra, Lorenzo Pavesi, Leonardo Ricci, and Emanuele Scifoni. Our tasks will include guiding and overseeing a smooth running of the PhD school, while also making related decisions at important times, and obviously helping an otherwise overburdened Raffaello as coordinator. Undoubtedly a very important responsability, given we are talking about the programme which produces our PhD graduates. I look forward to working with my fellow committee members over the next years!
IOP Trusted Reviewer Status
I’m extremely glad to have been awarded the status of IOP Trusted Reviewer! This is a certification from the Institute of Physics (IOP) which recognizes the best reviewers for IOP journals, in recognition of an exceptionally high level of peer review competency, as rated by the editors (more specifically, it recognizes “a high level of peer review competence, with the ability to critique scientific literature to an excellent standard”). In practice, it recognizes reviewers who consistently submit good reviews. The IOP journals I regularly review for (which are also journals where I regularly publish my papers) are JCAP and CQG. I believe in the value of peer review and put significant efforts into ensuring my reviews are always detailed and helpful for the authors, so I am glad this has been officially recognized!
Visit by Françoise Combes
For the next two days we have the pleasure of hosting Prof. Françoise Combes, a renown astrophysicist from Collège de France. Françoise is here as visiting chair within the University of Trento-College de France visiting chair program. She will be delivering a seminar by the title of “Black Holes and Active Galaxy Nuclei” and a colloquium by the title of “The Puzzle of Dark Matter”. With the rest of our group we had a nice lunch together at Orostube in Povo, where the carbonara pizza I ate was particularly good and worthy of a picture! Welcome Françoise!
Media INAF coverage for Laniakea paper
Media INAF, the official news bulletin of INAF, the Italian National Institute for Astrophysics, posted a very nice interview to Leo Giani discussing the results of our Laniakea paper recently published in JCAP. The interview is in Italian, but Google translate does a good job, and you can read it here:
www.media.inaf.it/2024/02/12/laniakea-tensione-hubble/
Enjoy the read, and once more excellent job on this paper Leo!
Laniakea paper published in JCAP!
My paper on Laniakea with Leo Giani, Cullan Howlett, Khaled Said, and Tam Davis, which I previously reported on in an earlier news item, has now officially been published in JCAP! The full bibliographic coordinates for the paper are JCAP 2401 (2024) 071. Here is the link to the paper (which is published Open Access).
Marco Calzà joins my group!
I’m really excited to welcome the first postdoc in my group! Today Marco Calzà joins my group as one of the 2 DARKTRACK-funded postdocs (of the two, the BH theorist). Marco did his PhD at the University of Coimbra under the supervision of João Rosa, working on a bunch of very interesting things BH-related, from superradiance to evaporation. His expertise and interests were simply a perfect fit for what I plan on doing within DARKTRACK, and I really look forward to working together. Welcome Marco (or, to be more precise, welcome back, since he was actually a BSc and MSc student here in Trento some years ago)!
CosmoVerse interview
As part of CosmoVerse’s “Meet our scientists” initiative, today I was interviewed on a number of things, both physics-related and non. You can read the interview here, and the answer to the last question may be particularly interesting for tennis fans!
Mattia Scotto joins my group!
My group keeps expanding, and now includes Mattia Scotto as well! He will be working on his Master’s thesis under my supervision, where we plan on studying various cosmological signatures of dark energy models featuring a negative cosmological constant (perfect timing given today’s new preprint!), and how the signatures we will find can help us distinguish these models from the cosmological constant of ΛCDM. Welcome Mattia, and I’m looking forward to our work together!
Negative cosmological constant and JWST (part 2)
Together with Nicola Menci, Shahnawaz Adil, Upala Mukhopadhyay, and Anjan Sen, today we posted a new preprint which is basically the sequel to our earlier negative cosmological constant and JWST paper published in JCAP. What we did here, in no small part thanks to Nicola’s contribution, was to perform a more thorough analysis of JWST data, which significantly strengthens our earlier conclusions and shows that a dark energy model featuring a negative cosmological constant is a very interesting candidate model in light of the JWST observations. One notable addition was our study not only of photometric observations, but also spectroscopic observations from the FRESCO survey, which again confirm the earlier results and at the same time make them much more robust. It was great fun working on this paper, and I learned a lot about high-redshift galaxies! You can read our results in the preprint we just posted on arXiv: 2401.12659.
CosmoVerse seminar
Today I delivered a CosmoVerse seminar by the title of Seven hints that early-time new physics alone is not sufficient to solve the Hubble tension, no surprise focused on my seven hints paper (slides here). The seminar was recorded and posted on YouTube, here is the link. A long and stimulating discussion followed, with several very interesting questions and comments from experts in the field, including Adam Riess, Vivian Poulin, and Leandros Perivolaropoulos. For other videos in this seminar series, check out the CosmoVerse YouTube channel. The next seminar from Stefano Anselmi is one which promises to be very interesting!
