My paper with with with Nicola Menci, Shahnawaz Adil, Upala Mukhopadhyay, and Anjan Sen, where we robustly compare a dark energy model featuring a negative cosmological constant against JWST data (see this earlier news item), has been accepted for publication in JCAP! The results are basically unchanged compared to our earlier version, with certain aspects of our analysis better clarified. You can read the preprint version of the paper on arXiv: 2401.12659.
Visit by Valerio Faraoni
For the next couple of weeks we have the great pleasure of hosting Valerio Faraoni, currently a Full Professor at Bishop’s University in Canada, and arguably one of the world experts on all things related to gravity. Valerio will also be delivering a seminar by the title of “A bird's eye view of the first-order thermodynamics of scalar-tensor gravity”. Welcome Valerio!
Attempting to solve the Hubble tension combining varying electron mass and ΛsCDM
I’m very, very glad to see my latest work with Yo Toda, William Giarè, Emre Özülker, and Eleonora Di Valentino finally out on arXiv after several months of hard work (especially by the first author Yo who did all the heavy lifting)! The idea is motivated by my seven hints paper (see this earlier news item) arguing that solving the Hubble tension may require a combination of pre- and post-recombination new physics, and here we attempted to construct precisely such a combination, focusing on models which individually worked well in the pre- and post-recombination era so far: a spatially uniform time-varying electron mass in a non-spatially flat Universe, and the ΛsCDM model, featuring a late-time sign-switching cosmological constant (from negative to positive). In the end the idea didn’t quite work, but we still decided to document our attempt because we learned a great deal about potential difficulties and drew what we hope are important general lessons for future endeavours: for the record, these are reported between Pages 10 and 13 and, spoiler, Ωm plays a crucial role in explaining why this didn’t work. A fun fact Özgür Akarsu reminded me of is that around minute 44 of my Universe Today Podcast interview with Fraser Cain back in November (see this earlier news item) I actually gave a very detailed spoiler of this project, as I had spoken to Yo a few days back so we had just gotten it started (and I had quite high hopes on this working out, which it certainly did in the sense of learning a whole lot of new things, although not in the way I initially expected). You can read our results in the preprint we just posted on arXiv: 2407.01173.
Visit by Benjamin Knorr
This week we have the pleasure to host Benjamin Knorr, currently a postdoc at NORDITA and arguably one of the world experts on asymptotic safety, a highly non-trivial generalization of the idea of perturbative renormalization. Benjamin also delivered a very nice talk by the title of “Asymptotic safety meets field redefinitions”. Welcome Benjamin!
New impact factor for Physics of the Dark Universe
Physics of the Dark Universe, the journal for which I am Editor, performed once again very well at the 2024 release of the annual Journal Citation Reports. Our updated impact factor (IF) for 2023 is 5.0 (the number reflects works published in 2021 and 2022, so still before my time)! This number has gone a bit down from our 2022 one, which was 5.5, yet remains high for the standards of the field. In fact, we are competitive with the other top-tier journals in cosmology and high-energy physics, such as PRD (4.6), PLB (4.3), JCAP (5.3), ApJ (4.8), and MNRAS (4.7), whose IFs all fall in the 4.5-5.5 ballpark. Huge thank you to everyone who helped us grow!
Scale-invariant inflation paper accepted in JCAP!
My paper with with with Chiara Cecchini, Mariaveronica De Angelis, William Giarè, and Max Rinaldi, where we tested a theoretically very well-motivated classically scale-invariant inflationary model against current cosmological data (see this earlier news item), has been accepted for publication in JCAP! There were a few minor changes in order to better clarify a few aspects of our analysis, but the results are completely unchanged with respect to the earlier version. You can read the preprint version of the paper on arXiv: 2403.04316.
Visit by Leonardo Giani
We are delighted to have Leonardo (Leo) Giani visiting us once more! Leo is a postdoc at the University of Queensland, where he is working on a bunch of very interesting things gravity- and cosmology-related, including our recent work on Laniakea. We took the opportunity to catch up on a few ideas which had been hanging around (and are turning into student projects), while Leo also gave a seminar by the title of “Cosmology from the point of view of an almost spherical cow”.
Solar chameleons revisited: 2024 edition
I’m extremely happy to see our latest work led by the brilliant Tomás (Tom) O'Shea, together with Anne Davis, my fellow countryman (we are both from Terracina) Maurizio Giannotti, Luca Visinelli, and Julia Vogel, out on arXiv! This was a technical tour-de-force led by Tom where we revisited the issue of production of chameleons (which could be relevant to the dark energy problem) in the Sun, whose state-of-the-art dated back to 2012, and partially motivated by the earlier work of myself, Luca, and Anne. The resulting spectrum includes a number of previously overlooked contributions which turn out to make an important difference, and our results can be extremely relevant for future experiments such as IAXO. While in our work we only included the contribution from transverse photons, the study of longitudinal plasmons is certainly relevant and in progress. You can read our results in the preprint we just posted on arXiv: 2406.01691.
Visit by Luca Visinelli
We are delighted to have Luca Visinelli visiting us once more! Luca is a Professor at the Tsung-Dao Lee Insittute in Shanghai Jiao Tong University: he is a very well-known scientist with broad research interests spanning dark matter, dark energy, and black holes. It was a very enjoyable visit during which we took the opportunity to catch up on our ongoing projects (especially replying to pending referee reports!) and enjoy the surroundings of Povo, while Luca also gave a seminar by the title of “Theoretical motivations for a light boson and its phenomenology”.
Visit to Camerino
Today and for the next two days I am visiting the University of Camerino, where I will be giving a talk on “Searching for dark energy off the beaten track” (see poster below, slides here). I will be hosted by Orlando Luongo, whom I look forward to meeting in person after reading his works for many years. I look forward to a nice visit in a charming city!
State of the dark energy equation of state paper published in JCAP!
My paper on the dark energy equation of state with Luis Escamilla, William Giarè, Eleonora Di Valentino, and Rafael Nunes, 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 2405 (2024) 091. Here is the link to the paper (which is published Open Access).
Teaching ends today (for now)
My teaching duties for the spring semester end today, after having covered in depth the second law of thermodynamics. The next month will be busy serving on various committees, after which I look forward to a couple of months almost entirely dedicated to research!
Visit by Francesco Di Filippo
We’re excited to welcome our latest visitor: Francesco Di Filippo from Charles University in Prague! Francesco, hosted by Max Rinaldi, is currently a postdoc at Charles University in Prague, where he has been doing a lot of interesting work especially on regular black holes and possible instabilities (or not) thereof, together with a bunch of experts in the field including Stefano Liberati and Matt Visser - he will be delivering a seminar at TIFPA by the title of “Non-singular black holes: Open issues and implications”. Welcome Francesco!
State of the dark energy equation of state paper accepted in JCAP!
My paper with with Luis Escamilla, William Giarè, Eleonora Di Valentino, and Rafael Nunes, where we present state-of-the-art constraints on the dark energy equation of state from a number of cosmological probes (see this earlier news item), has been accepted for publication in JCAP! There were a few changes, mostly making a few parts of the discussion clearer, but the results are otherwise completely unchanged compared to the previous version we posted this summer. You can read the preprint version of the paper on arXiv: 2307.14802.
Guan-Wen Yuan joins my group!
I’m really excited to welcome the third postdoc in my group! Today Guan-Wen Yuan (袁官文) joins my group as the second of the 2 DARKTRACK-funded postdocs (of the two, the astroparticle physicist), with the other being Marco Calzà. Guan-Wen did his PhD at the University of Science and Technology of China and at Purple Mountain Observatory under the supervision of Jin Chang, PI of the DAMPE experiment, and working on a bunch of very interesting things related but not limited to dark matter, BHs, and gravitational waves. And with the arrival of Guan-Wen our group is now complete. Now we just need to get lots of excellent science out. Welcome to Italy Guan-Wen!
Admissions for PhD in Physics in Trento!
The University of Trento welcomes applications for admission to the 40th cycle of the PhD in Physics, for positions starting on November 1, 2024 (see here for Italian link, here for English link, and here for much more detailed information): this year we have a total of 19 positions, 14 of which with scholarship, and 4 of which are “open positions”, i.e. not tied to any specific topic. Applicants interested in working within the Theoretical Gravitation and Cosmology group (basically either with me or Prof. Rinaldi) would be competing for these 4 “open positions” - however, another possible channel for working with us is to apply for one of the 3 INFN funded-positions (Section “D, E - Particle, astroparticle, nuclear, theoretical physics, related technologies and applications, including medical Physics”), which are de facto “open positions” (as long as the topic one ends up working on is related to INFN research themes, for instance the group’s current PhD students Chiara Cecchini and Davide Pedrotti were awarded one of these positions). I cannot stress enough that competition for these positions is extremely strong, with an oversubscription ratio much higher than for the other (reserved) positions: a corollary is that there is no guarantee our group will be taking new PhD students, given that it really depends on the personal interests of those who will be awarded these positions (however, I can anticipate that I will be taking a most one new PhD student - for a rough guideline on possible topics one could work on with me, please see this link, section “First call 40°cycle - Other research topics”, subsection “FT - Theoretical and computational physics”, and refer to the topic “Dark matter and dark energy in the era of precision multi-messenger cosmology and cosmic tensions (Vagnozzi)”). If you are interested in working with us, please make this very clear in your “lettera motivazionale” (“statement of purpose”), which plays an extremely important role in the evaluation of candidates, so please take it very seriously. The application deadline is May 15, 2024 at 16:00 Italy time, but applicants are strongly encouraged to apply well in advance of the deadline - if you are interested in working within our group, please do not hesitate to reach out either to me or Prof. Rinaldi (or both) and apply as soon as possible!
Quasinormal modes-shadow correspondence for rotating regular black holes
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!
