A recent piece in Scientific American, mainly focused on this recent paper on tests of asteroid-mass primordial black holes from Solar System ephemerides, dedicated a paragraph to our recent paper in Communications Physics on using the asteroid Bennu to test dark matter and other aspects of fundamental physics (see this earlier news item), with quotes from first author Yu-Dai Tsai. Here is a link to the piece in Scientific American:
www.scientificamerican.com/article/dark-matter-black-holes-could-fly-through-the-solar-system-once-a-decade/
Varying electron mass and ΛsCDM paper accepted in PDU!
My paper with Yo Toda, William Giarè, Emre Özülker, and Eleonora Di Valentino, where we attempt to solve the Hubble tension combining 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 (see this earlier news item), has been accepted for publication in PDU! Minor revisions compared to the previous version include a small change to the title, small updates to the figures and tables for consistency, and especially a proper Bayesian evidence-based model comparison analysis. You can read the preprint version of the paper on arXiv: 2407.01173.
Teaching feedback
I just received the feedback from students of the courses I delivered last semester (again General Physics I part 2 and Advanced Topics in Theoretical Physics). As with last year, the feedback was excellent, with a satisfaction index of 100% (which in turn gives me lots of satisfaction): particularly appreciated were my efforts to develop the students’ physical intuition, which is something I indeed consistently pay particular attention with. Again, these positive comments will motivate me to do even better next time (when I will also be taking over the Special Relativity course, after decades during which Luciano Vanzo taught it - a rather big pair of shoes to fill)!
Science News interview
I was recently interviewed by Emily Conover for Science News on the puzzling status of cosmological neutrino mass constraints after DESI, with part of the discussion motivated by my recent paper on the topic. It was very nice to chat with an amazing and tremendously well-known journalist such as Emily (whose pieces I highly recommend)! Her extremely nice piece appeared today and, besides from myself, contains quotes from a number of well-known scientists, including Licia Verde, Dan Green, Willem Elbers, as well as my friends and colleagues Miguel Escudero and Eleonora Di Valentino. You can read the full article here:
www.sciencenews.org/article/neutrino-mass-phenomenon-cosmology
I had great fun talking to Emily, and I hope you enjoy the interview!
Fifth forces and Bennu paper published in Communications Physics!
My paper with Yu-Dai Tsai, Davide Farnocchia, Marco Micheli, and Luca Visinelli, where we use OSIRIS-REx tracking data for the asteroid Bennu to set new constraints on fifth forces and ultralight dark matter (see this earlier news item), has now officially been published in Communications Physics (making this my first proper Nature publication)! The full bibliographic coordinates for the paper are Commun. Phys. 7 (2024) 311. Here is the link to the paper (which is published Open Access).
Top 2% scientists (2023 edition)
As with last year, for what it’s worth, it looks like my name appeared in the list of top 2% scientists worldwide, compiled by John Ioannidis at Stanford University, and available here. It seems that for the year 2023 I’ve been ranked 2633rd across all fields, and 28th in my area (looks a bit too high, perhaps it’s because some Scopus research evaluation tool thinks my main area is Nuclear & Particle Physics rather than Astronomy & Astrophysics), whereas considering my whole career the numbers become 67934th and 1228th respectively. Again, all the caveats highlighted last year apply.
Farewell to Jun-Qian Jiang
Today we say farewell to Jun-Qian Jiang, who after an extremely successful 6 months as a long-term visiting PhD student, is returning to China (below is a picture from our farewell pizza dinner at Doc: from left to right we have Simony Santos da Costa, Marco Calzà, Guan-Wen Yuan, Jun-Qian Jiang, and yours sincerely). Jun-Qian’s time here was extremely productive, with 3 very interesting papers, many more in the making, and several key contributions to my group’s activities, for which his arrival was extremely important. Thanks a lot Jun-Qian for everything you taught me, and have a nice trip back to China!
Solar chameleons paper published in PRD!
My paper with Tom O'Shea, Anne Davis, Maurizio Giannotti, Luca Visinelli, and Julia Vogel, where we revisited the issue of production of Solar chameleons (see this earlier news item), has now officially been published in PRD! The full bibliographic coordinates for the paper are Phys. Rev. D 110 (2024) 063027. Here is the link to the paper (which is published Open Access).
Primordial regular black holes (part 2)
A truly busy day today, as with Marco Calzà and Davide Pedrotti we posted not one but two papers! In our first paper, covered in this other news item and motivated by the fact that all studies on primordial black holes (PBHs) consider Schwarzschild and Kerr BHs which feature curvature singularities, we took a first step towards studying primordial regular BHs as dark matter (DM) candidates, focusing on phenomenological tr-symmetric metrics. In this paper, we extend our pilot study to non-tr-symmetric metrics, which complicate our work by a fair margin. Aside from the well-known Simpson-Visser metric, the space-times we studied include two metrics inspired by Loop Quantum Gravity, more specifically the Peltola-Kunstatter and D’Ambrosio-Rovelli ones, and in all three cases we find that the “asteroid mass window” where all the DM can be made of PBHs is enlarged. You can read our results in the preprint we just posted on arXiv: 2409.02807.
Primordial regular black holes (part 1)
I would be lying if I didn’t say I am particularly proud of this new paper which appeared today with Marco Calzà and Davide Pedrotti, making it another made in Trentino paper and, especially, another paper entirely produced within my group (note that this paper is for 2/3 made within the Valle dei Laghi, which is where both Marco and Davide originally come from)! There are a huge number of studies on primordial black holes (PBHs) as potential dark matter (DM) candidates, yet virtually (almost) all of these works consider Schwarzschild or Kerr BHs, which suffer from a few well-known problems, including the presence of curvature singularities. In today’s paper we therefore took a first step towards characterizing primordial regular BHs (which, on the contrary, do not feature curvature singularities) as DM candidates, finding that they can potentially lead to a larger “asteroid mass window” where PBHs can make up all the DM. Today’s pilot study is focused on so-called tr-symmetric metrics, which include the well-known Bardeen and Hayward regular BHs, whereas we have also put out a companion paper (covered in this other news item), where we study non-tr-symmetric metrics, which also include metrics inspired from Loop Quantum Gravity. You can read our results in the preprint we just posted on arXiv: 2409.02804.
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.
Solar chameleons paper accepted in PRD!
My paper with Tom O'Shea, Anne Davis, Maurizio Giannotti, Luca Visinelli, and Julia Vogel, where we revisited the issue of production of Solar chameleons (see this earlier news item), has been accepted for publication in PRD! Minor revisions compared to the previous version include a rough estimate of how much the CAST bound on the chameleon-photon coupling changes accounting for the production channels we studied. You can read the preprint version of the paper on arXiv: 2406.01691.
Fifth forces and Bennu paper accepted in Communications Physics!
Very happy to report that my paper with Yu-Dai Tsai, Davide Farnocchia, Marco Micheli, and Luca Visinelli, where we use OSIRIS-REx tracking data for the asteroid Bennu to set new constraints on fifth forces and ultralight dark matter (see this earlier news item), has officially been accepted for publication in the prestigious Communications Physics, part of the Nature Portfolio collection of journals (it is my second time publishing in Nature journals after my 2020 book review in Nature Astronomy, but only the first time publishing a proper original scientific article)! It was quite a long journey, with a couple of rounds of revision on both the scientific and editorial sides, although overall there were no major changes to our results which, if anything, have been clarified better. You can read the preprint version of the paper on arXiv: 2309.13106.
Hubble tension, Ωm, and ωc
A very busy week, with another paper produced almost entirely within my group, just in time for wrapping up for holidays! With Davide Pedrotti, Jun-Qian Jiang, Luis Escamilla, and Simony Santos da Costa, we argue that the Hubble tension is inherently multidimensional, and that the matter density parameter Ωm and cold dark matter physical density ωc play key roles. In particular, we analytically explained why any model aiming to solve the Hubble tension will inevitably lead to an increase in ωc (because both Ωm and ωb are precisely calibrated by BAO and/or SNeIa, and BBN respectively) and, by extension, S8 (with potential problems for the S8 discrepancy), and explicitly verified that this holds on real data. We then argued that if cosmologists interested in solving the Hubble tension could ask for just one present from Father Christmas…well, then they really should wish to know the value of Ωm chosen by Nature - or, in practical terms, they should wish for a calibration of Ωm which is as reliable and model-independent as possible, and we put forward some ideas on how to achieve this. You can read our results in the preprint we just posted on arXiv: 2408.04530.
EHT and mimetic gravity
Another exciting paper out today! With Mohsen Khodadi and Javad Firouzjaee, we show that the Event Horizon Telescope (EHT) observations basically rule out compact objects in mimetic gravity, a framework of modified gravity which has received a lot of interest as a candidate for explaining both dark matter and dark energy, and first proposed (explicitly) by Mukhanov and Chamseddine in 2013. Mohsen and collaborators studied compact objects in mimetic gravity in 2020, finding them to be highly non-trivial: in practice, the theory supports only a naked singularity, and a black hole obtained through a particular gluing procedure. What we showed in today’s paper is that the shadow properties of both these space-times are pathological, since the naked singularity does not cast a shadow, whereas the black hole casts a shadow which is way too small: for these reasons, both compact objects (and by extension mimetic gravity or, more precisely, the baseline version proposed in 2013) appear to be excluded by the EHT images of M87* and Sgr A*. You can read our results in the preprint we just posted on arXiv: 2408.03241.
Non-parametric expansion history reconstruction and Hubble tension after DESI
I’m particularly excited and proud about today’s paper, which is the first one written entirely and exclusively with members of my group: visiting PhD student Jun-Qian Jiang (who did all the heavy lifting), PhD student Davide Pedrotti, and postdoc Simony Santos da Costa. What we did has been to perform a non-parametric reconstruction of the late-time expansion history in light of DESI BAO data, combined with various SNeIa datasets, using both interpolation and Gaussian Process reconstruction techniques, and studying implications for the Hubble tension. We find that the shape of the expansion history cannot deviate more than 10% from that of ΛCDM, but within that 10% we find interesting deviations which could hint to a non-monotonic/oscillatory behaviour of the expansion rate (and therefore of the dark energy component). I really believe that this can be a pretty important paper, as it represents a much needed revisitation in light of DESI of two seminal papers in the expansion history reconstrcution and Hubble tension literature: the famous “Trouble with H0” paper by Bernal, Verde, & Riess, and the equally famous “Sounds discordant” paper by Aylor and collaborators. You can read our results in the preprint we just posted on arXiv: 2408.02365.
Congratulations to Giovanni Piccoli!
Congratulations to Giovanni Piccoli, who has been offered a PhD position at the University of Zurich, in the group of Jaiyul Yoo! Giovanni will be leaving my group in September to move to Zurich. Congratulations Giovanni, good luck for this new adventure in your life, and looking forward to reading your works!
Negative cosmological constant and JWST paper (part 2) published in JCAP!
My paper 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 now officially been published in JCAP! The full bibliographic coordinates for the paper are JCAP 2407 (2024) 072. Here is the link to the paper (which is published Open Access).
Post-DESI neutrino cosmology
Another paper out today! Led by Jun-Qian Jiang and William Giarè (both of whom did a huge amount of work), and together with Stefano Gariazzo, Maria Giovanna Dainotti, Eleonora Di Valentino, Olga Mena, Davide Pedrotti, and Simony Santos da Costa, we investigate the status of (positive) neutrino mass cosmology after the latest DESI measurements. We find very tight upper limits on the sum of the neutrino masses, a strong preference for the normal ordering, and a significant tension with terrestrial observations, all of which we carefully quantify. We also studied the impact of allowing the dark energy component to be non-phantom, which makes all the previous conclusions somewhat stronger, and highlights an interesting synergy between laboratory experiments aimed at determining the neutrino mass ordering, and the nature of dark energy. You can read our results in the preprint we just posted on arXiv: 2407.18047.
Scale-invariant inflation paper published in JCAP!
My paper on scale-invariant inflation with Chiara Cecchini, Mariaveronica De Angelis, William Giarè, and Max Rinaldi, 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 2407 (2024) 058. Here is the link to the paper (which is published Open Access).
