Solar chameleons and XENONnT paper published in PRD!

My paper with Guan-Wen Yuan, Anne Davis, Maurizio Giannotti, Luca Visinelli, and Julia Vogel, where we set new constraints on solar chameleons from XENONnT electron recoil data (see this earlier news item), has now officially been published in PRD! The full bibliographic coordinates for the paper are Phys. Rev. D 113 (2026) 123024. Here is the link to the paper (which is published Open Access).

Solar chameleons and XENONnT paper accepted in PRD!

My paper with Guan-Wen Yuan, Anne Davis, Maurizio Giannotti, Luca Visinelli, and Julia Vogel, where we set new constraints on solar chameleons from XENONnT electron recoil data (see this earlier news item), has been accepted for publication in PRD! There were relatively minor changes compared to the earlier version, especially concerning the publicly available code. You can read the preprint version of our paper on arXiv: 2511.01655.

Acoustic reheating and relic neutrinos

I’m extremely happy to see my latest paper with my oustanding former MSc student Giovanni Piccoli and Joe Silk out on arXiv - congratulations to Giovanni who did basically all the work, in what is essentially the result of his MSc thesis! This paper is based on the idea of acoustic reheating, i.e. the dissipation of small-scale perturbations through diffusion damping (a process which at recombination is known as Silk damping), which injects entropy into the photon bath. For certain modes, the dissipation occurs after neutrino decoupling, meaning that this entropy is not shared by the neutrinos, which are therefore colder than expected: we showed that these modifications can potentially show up in experiments aimed at detecting relic neutrinos such as PTOLEMY, which can therefore set constraints on the small-scale power spectrum. This idea has been in the back of my mind ever since I moved to Cambridge as a postdoc 2019 (in fact you can find it “discussed” on my Cambridge whiteboard in this picture appearing in my webpage), and for various reasons took much longer than it should have to appear, so I am extremely happy that it is finally out: plus, it doesn’t happen every day to write a paper on Silk damping with Joe Silk himself! You can read the results in the preprint we just posted on arXiv: 2605.11956.

Beyond ΛCDM with JWST paper published in JHEAp!

My paper with Leonardo Comini and Avi Loeb, where we revisit the “JWST tension” in models beyond ΛCDM and with spectroscopic data (see this earlier news item), has now officially been published in JHEAp! The full bibliographic coordinates for the paper are JHEAp 53 (2026) 100626. Here is the link to the paper (which is published Open Access).

Farewell to Guan-Wen Yuan

Today we say farewell to Guan-Wen Yuan, who after an extremely successful 2 years as a postdoc in my group, is now returning to China to take up a position as Associate Research Professor at USTC. To say goodbye to Guan-Wen, a bunch of us from the Theoretical Gravitation and Cosmology Group went for an extremely nice Chinese dinner at China Gusto, easily one of the best Chinese places in Trento: below is a picture of us, from left to right we see Luciano Vanzo, Max Rinaldi, Sergio Zerbini, Marco Calzà, Guan-Wen Yuan, yours sincerely, Davide Pedrotti, and Miguel Sabogal. Guan-Wen’s time here was extremely productive, and aside from our 2 papers together he made several important contributions to my group’s activities. Thanks a lot Guan-Wen for everything you taught me, and best of luck for the next chapter of your career back in China!

Admissions for PhD in Physics in Trento!

The University of Trento welcomes applications for admission to the 42nd cycle of the PhD in Physics, for positions starting on November 1, 2026 (see here for Italian link, here for English link, scroll to “Bando di ammissione” and “Admission call” respectively, and here for much more detailed information): this year we have a total of 19 positions, 15 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 should note that I do not plan on taking PhD students this year, so there is little point applying and expressing interest in working with me. On the other hand, Prof. Rinaldi would be interested in taking a PhD student to work on cosmologically coupled black holes, see here for more information. Applicants interested in working with Prof. Rinaldi would be competing for these 4 “open positions” (those referred to as “University of Trento” in the Table on Page 2 of the admission call) - however, another possible channel in this direction is to apply for one of the 2 INFN funded-positions (Section “F, G - Particle, astroparticle, nuclear, theoretical physics, related technologies and applications, including medical Physics”), which are de facto “open positions” and in the past have funded PhD students in our group. Competition for these open positions is extremely strong, with an oversubscription ratio much higher than for the other (reserved) positions: therefore, if you are interested in working with Prof. Rinaldi, 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 19, 2026 at 16:00 Italy time, but interested applicants are strongly encouraged to apply well in advance of the deadline.

Visit by Carsten van de Bruck

Today we have the pleasure of hosting Carsten van de Bruck, visiting us from Sheffield! Carsten is currently a Professor at the University of Sheffield, and is a recognized expert on theoretical cosmology, particularly for what concerns modified gravity models for inflation and dark energy, and their observational tests. He will not be delivering a talk, but is here as one of the external opponents for Chiara Cecchini’s PhD defense (which, by the way, was outstanding - you can find her PhD thesis on scale-invariant inflationary models here). Welcome Carsten!

Beyond ΛCDM with JWST

I’m very happy to see my latest paper with my former MSc student Leonardo Comini and Avi Loeb out on arXiv - congratulations to Leonardo who did a significant part of the work, in what is basically the result of his MSc thesis! This work is basically an extension of Mike Boylan-Kolchin’s 2023 paper arguing that early JWST photometric data put significant pressure on the ΛCDM model. We basically asked the question of how this result changed if: 1) a proper Bayesian analysis was carried out, 2) considering also models beyond ΛCDM (e.g. models with a free equation of state or spatial curvature), and 3) using also spectroscopic data which is more reliable? The answer is that carrying out this analysis photometric data actually no longer requires an unusually high star formation efficiency, unlike (surprisingly) spectroscopic data, with the results not changing significantly in models beyond ΛCDM: the conclusion is that the origin of the “JWST tension” is likely astrophysical rather than cosmological. You can read the results in the preprint we just posted on arXiv: 2604.13866.

Multi-field early dark energy

I’m extremely excited to see my latest paper with my outstanding MSc student Marco Bella, Vivian Poulin, and Lloyd Knox out on arXiv - congratulations to Marco who did basically all the work, in what is essentially the result of his MSc thesis! The canonical 1-field axion early dark energy (EDE) model which Vivian and collaborators developed a few years ago faces extremely tight constraints when confronted against Planck PR4 CMB data. In this work we asked ourselves: what happens if we introduce more than 1 axion, a scenario which for instance can be strongly motivated by the string axiverse? The answer is that having 2 axions can significantly help, basically halving the residual Hubble tension even when confronted against Planck PR4 CMB data, whose fit is drastically improved by the fact that the modifications to the expansion history now span a wider redshift range, including the epoch closer to recombination (although, interestingly, having more axions does not seem to improve these results). You can read the results in the preprint we just posted on arXiv: 2604.13535.

Visit by Antonio Racioppi

Today we have the pleasure of hosting Antonio Racioppi, visiting us from Tallinn! Antonio is currently a senior researcher at the National Institute of Chemical Physics and Biophysics (NICPB) in Tallinn, working especially on the construction of inflationary models beyond General Relativity. He will be delivering a talk by the title of “Inflation in metric-affine gravity”. Welcome Antonio!

Marco Bella’s MSc defense

Congratulations to Marco Bella, who today successfully defended his MSc thesis, by the title of “Multi-axion early dark energy and the Hubble tension” (with the opponent being Prof. Albino Perego)! Marco’s defense was absolutely outstanding, and he received top grades and honours, i.e. 110 e Lode (with this being the fourth 100 e Lode for my MSc students, after Davide Pedrotti, Giovanni Piccoli, and Mattia Scotto). In his thesis which I supervised together with Vivian Poulin, Marco studied multi-field axion early dark energy models, with the goal of seeing whether they can further improve over the vanilla early dark energy model in the context of the Hubble tension (as a spoiler, the answer is yes, and we are preparing a paper on the topic to appear soon, so stay tuned!), while developing and publicly releasing the mAxiCLASS Boltzmann solver. Marco will be starting his PhD later this year at UC Davis, where he will be working with Lloyd Knox. During the same day, I also served as opponent for Sara Marini and Jesa Crapella, respectively MSc students of Prof. Albino Perego and Prof. Alessandro Roggero, who discussed theses on binary neutron star mergers and non-superfluid neutron stars.

Alessandro La Sala’s BSc defense

Congratulations to Alessandro La Sala, who today successfully defended his BSc thesis (for the BSc degree in Mathematics), by the title of “Relatività Generale: uno studio della soluzione di Schwarzschild e applicazioni”, which translates to “General Relativity: a study of the Schwarzschild solution and applications” (with the opponent being Prof. Sonia Mazzucchi)! In his thesis which I supervised, Alessandro discussed some basic aspects of General Relativity, before turning to features of the Schwarzschild solution.

Andrea Di Pompeo's BSc defense

Congratulations to Andrea Di Pompeo, who today successfully defended his BSc thesis, by the title of “Correlazioni EPR in spaziotempo curvo”, which translates to “EPR correlations in curved spacetime” (with the opponent being Prof. Max Rinaldi)! In his thesis which I supervised, Andrea discussed the effects of spacetime curvature on non-local quantum correlations between entangled pairs of spins, with a focus on Bell-type correlations (and in particular CHSH correlations), a work far from trivial for a BSc student.

Tonale Winter school organization

As of today, I’ve officially entered the organizing team for the Tonale Winter School, a well-known cosmology winter school addressed to advanced MSc students, PhD students, and junior postdocs, which started in 2007 and takes place in Passo del Tonale, Italy. I am taking over Max Rinaldi, who has stepped down after being an organizer for several years. I myself attended the school as a student in 2014 and as a lecturer in 2023. I’m really excited to get started, and stay tuned for more updates on the 2026 edition!

Visit by Kevin Croker

For the rest of the month we have the great pleasure of hosting Kevin Croker, currently an Assistant Research Scientist at Arizona State University. Kevin is especially well known for his work on cosmologically coupled black holes. He will be delivering a few lectures on the topic, specifically on constrained variations and their impact on cosmological dynamics. Welcome Kevin!

Teaching restarts today

Today my teaching duties restart once more! For the rest of the semester I’m looking at an extremely busy schedule (as detailed on my office door) where I’ll once again be teaching Classical Thermodynamics for the Mathematics BSc, Relativity for the Physics BSc, and Modern Cosmology for the Physics MSc. During these busy months I’m basically guaranteed to do almost no research, so hopefully my collaborators will understand 🤪 As in previous years, all my teaching material will be made publicly available on the English and Italian versions of my teaching page.

BAO and Hubble tension no-go theorem paper published in PRD!

My paper with Davide Pedrotti, Luis Escamilla, Valerio Marra, and Leandros Perivolaropoulos, where we show that the “Hubble tension no-go theorem” forbidding purely post-recombination solutions is robust against a possible miscalibration of BAO measurements, while highlighting the very important role of unanchored SNeIa (see this earlier news item), has now officially been published in PRD, where it has been selected as an Editors’ Suggestion (see this earlier news item)! The full bibliographic coordinates for the paper are Phys. Rev. D 113 (2026) 043507. Here is the link to the paper (which is published Open Access).

Edvig Selimaj joins my group!

Today Edvig Selimaj officially joins my group, and will be carrying out his Master’s thesis under the supervision of myself and Miguel Sabogal. We plan to work on non-parametric reconstructions of the expansion history in light of state-of-the-art cosmological datasets, and then apply a number of machine learning methods to these reconstructions to learn more about dark energy. Welcome Edvig, and I’m looking forward to our work together!

Gruppo 2003

As of today, I’m honored to be a member of Gruppo 2003! This is a group which brings together some of the most influential Italian scientists (including for instance Giorgio Parisi, here is the full list of members), with the aim of improving the far from ideal situation of scientific research in Italy. The group is also responsible for the online journal Scienza in Rete, and holds a certain political influence. Needless to say I’m honored to have been invited to join the group, and I hope I’ll be able to give my contribution to improving the state of research in Italy!