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.
New impact factor for Physics of the Dark Universe
The 2023 release of the annual Journal Citation Reports from Clarivate Analytics has now been made public, and with it the updated impact factors (IFs) for several journals. I am thrilled to announce that the journal of which I am Editor, Physics of the Dark Universe, performed extremely well, with a 2022 IF of 5.5! For the full list of IFs, see this document. This confirms once more the high impact of papers published in PDU, which places us at a level comparable to journals such as PRD (5.0), PLB (4.4), JCAP (6.4), ApJ (4.9), and MNRAS (4.8), just to mention a few. Please consider submitting your next paper to PDU!
Three recent talks
In the past three days I delivered three (online) seminars, all by the title of Seven hints that early-time new physics alone is not sufficient to solve the Hubble tension. I gave the talks “at” IPM, Tehran (Iran); the Institute of Advanced Studies in Science and Technology of Babes-Bolyai University (Romania), within Tiberiu Harko’s highly recommended seminar series in Gravitation, Cosmology, and Astrophysics; and at the conference Recent Advances in Mathematical Sciences and Interdisciplinary Areas 2023 at GLA University (India). I basically reported about a work in progress which I expect will be out in the next three months (so stay tuned!), and all the slides are available on my talks page. A pictorial summary of the work, made by my wife, is shown below.
Tonale Winter School on Cosmology
I’m pleased to announce that I will be lecturing at the Tonale Winter School on Cosmology later this year. This is 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 myself attended as a student in 2014. This year I will deliver 4 lectures on cosmological tensions. More details, including the official school page, will follow later!
Teaching ends today (for now)
Today marks the end of the teaching period, which will restart in September. Now of course it’s time for exams (already the coming Monday)! While it was truly nice to be able interact with many bright young minds, teaching two and a half courses was also particularly heavy, I’m not gonna lie, so I really look forward to a couple of months where I will be able to mostly focus on research. So, hopefully, several new papers should come out in the next months. Stay tuned!
Giovanni Piccoli joins my group!
My group is expanding, and as of today includes also Giovanni Piccoli. He will be working on his Master’s thesis under my supervision, and we plan to explore novel cosmological and terrestrial tests of the (very) small-scale matter power spectrum - no spoilers, you’ll have to wait and see what we come up with! Welcome Giovanni, and looking forward to our work together!
Sgr A* horizon-scale tests paper accepted in CQG!
I’m really excited that my paper on horizon-scale tests of gravity theories and fundamental physics from the Event Horizon Telescope (EHT) image of Sagittarius A* (Sgr A*) has been accepted for publication in CQG! This is a huge paper I led with 14 other authors spread throughout the world (our countries of affiliation include Italy, UK, China, USA, India, Iran, Canada, South Africa, North Macedonia, and Turkey): Rittick Roy, Yu-Dai Tsai, Luca Visinelli, Misba Afrin, Alireza Allahyari, Parth Bambhaniya, Dipanjan Dey, Sushant Ghosh, Pankaj Joshi, Kimet Jusufi, Mohsen Khodadi, Rahul Kumar Walia, Ali Övgün, and Cosimo Bambi. We used the EHT image of Sgr A* to test over 50 well-motivated theoretical scenarios, ranging from theories of gravity, novel fundamental physics frameworks, and black hole mimickers such as naked singularities and wormholes. This paper was initially (see v1) written only with Rittick, Yu-Dai, and Luca, tirelessly and also shamelessly ambulance-chased over a weekend following the exciting EHT announcement on May 12, 2022, but was then substantially polished and extended throughout summer 2022 with the addition of all the new authors - it is easily one of the most impactful papers I’ve ever written and at the same time likely the paper that drained the most energy out of me, and I’m really relieved to finally see it accepted for publication, after a very long refereeing process (one of the referee reports was a 4-page long pdf in 10pt font!). You can find the preprint version of the paper on arXiv: 2205.07787.
Visit by Michael Zantedeschi
This week we have Michael Zantedeschi, currently a postdoc at the Tsung-Dao Lee Institute, Shanghai Jiao Tong University (in the group of Luca Visinelli), visiting us for a couple of days. Michael is actually not new to Trento, having been an undergrad here (although he arrived just after I finished my undergrad, so we never overlapped). While we aren’t directly working together (yet), we will be brainstorming ideas related to screened dark energy, as well as the mysterious cosmological constant. Welcome Michael!
PhD positions at the University of Trento
The selection for admission to the 39th cycle of the PhD in Physics at the University of Trento is now open, see this link. For interested students not familiar with the procedure, this is done at a centralized (departmental) level, rather than by individual supervisors, through a committee of (typically) four people, which varies each year. There are a total of 22+1 positions, 19+1 of which with scholarship, of which 15+1 on a specific topic and the remaining 4 “free”: since I am not funding any “specific topic” position, students interested in working with me will have to compete for the 4 free fellowships, which means that there is no guarantee I will actually get to have an incoming PhD student this year - note that competition for these free fellowships is typically extremely tough, and it is recommended that if you are interested in working with someone specific, you should explicitly mention this in the cover letter. For a rough guideline on possible topics one could work on with me, please see this link (Section “First call 39° cycle - Other research topics”), and refer to the topics “Dark matter and dark energy in the era of precision multi-messenger cosmology and cosmic tensions (Vagnozzi)” and “Black holes as windows onto fundamental physics (Vagnozzi)” (note, however, that these are not binding). The deadline for applying is May 31 at 16:00 Italy time - please spread the word, and apply if you are interested!
Visit by Leonardo Giani
More visitors! This week we have Leonardo (Leo) Giani, currently a postdoc at the University of Queensland, visiting us for a couple of days. Leo and I are working on a very exciting project, which (spoiler) has to do with Laniakea, our home in the Cosmos, while also discussing other ideas more or less related to dark energy and cosmological tensions. Leo will also be delivering a seminar by the title of “Doctor suggests a new diet for Non-local gravity”. Welcome Leo!
Media coverage for asteroid paper
Our work the use of asteroids to search for fifth forces has been picked up by Vice, who interviewed first author Yu-Dai Tsai. You can read their piece here:
www.vice.com/en/article/z3mx4a/scientists-want-to-use-asteroids-to-search-for-hidden-fifth-force
Asteroid and fifth forces paper published in JCAP!
My paper with Yu-Dai Tsai, Youjia Wu, and Luca Visinelli on the use of asteroids as a probe of fifth forces, 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 2304 (2023) 031. Here is the link to the paper.
SIGRAV Prize!
I am honored to announce that I have been awarded the 2023 SIGRAV Prize (yes, given the day, I did initially think this was an April’s Fool)! This is one of the most prestigious Italian early-career awards in my field, and is awarded by the Italian Society for General Relativity and Gravitation (SIGRAV) to under-40 promising Italian researchers who have made important contributions to the fields of gravitation, astrophysics, and cosmology. It is a true honor to receive this Prize, which boasts a prestigious list of previous winners, back then young but now all tremendously successful researchers and most of them leaders in their fields, among whom (just to name a few): Augusto Sagnotti, Massimo Bianchi, Massimo Giovannini, Paolo Pani, Alessandra Buonanno, Alberto Vecchio, Rosalba Perna, Mariafelicia De Laurentis, Enrico Barausse, Marica Branchesi, and Davide Gerosa. I will be receiving the Prize (a silver medal) and delivering a plenary talk about my work at the XXV SIGRAV conference in Trieste this September, where the other winners will also be awarded (the other SIGRAV Prize has been awarded to Giulia Gubitosi, whereas the Amaldi medals have been awarded to my colleague and collaborator Joe Silk and Gabriele Veneziano). It is always great to be recognized in one’s home country, and I would like to sincerely thank my mentors and collaborators, without whom this would not have been possible!
ERC Starting Grant evaluation report
Today I received the evaluation report for Step 1 of my ERC Starting Grant application, which was unsurprisingly unsuccessful - as I promised in an earlier news item, I have decided to openly report the outcome of the evaluation to help normalize otherwise taboo discussions about lack of success in academia. I received a “B” (proposal of high quality but not sufficient to pass to Step 2 of the evaluation), which means I am blocked from applying for a further year. The comments from the 4 reviewers were actually extremely positive (their ratings included 7 “exceptional”, 3 “excellent”, and 2 “very good”), and the high-risk high-gain nature of the project was clearly appreciated. The main issue identified by more than one reviewers was that I probably put too much at once - a subset of the proposal focusing on 2/3 of the ideas I put out there would probably have stood a much better chance. This was a very useful experience, the reviewer comments were very helpful and I have to say somewhat reassuring, so at this point there’s not much more I can do than roll up my sleeves, while looking forward to trying again in 2024 taking this feedback into account!
Visit by William Giarè
This week we have William Giarè visiting us from the University of Sheffield, funded by a CosmoVerse COST STSM grant, as reported in this earlier news item. We’ll be finalizing a project exploring the state of the dark energy equation of state (pun intended), while starting up a number of other projects somewhat broadly related to cosmological tensions and the nature of dark energy. Looking forward to an exciting week of science!
Caritro Postdoctoral Fellowship
We’re hiring, or rather, trying to hire! The call for the 2023 Caritro Postdoctoral Fellowships is open, and the Theoretical Gravitation and Cosmology group led by Max Rinaldi and myself expects to be able to support at most one application. Caritro Fellowships are founded by the Caritro Foundation, and are meant to offer opportunities for professional growth to young researchers who have not turned 35 years old at the start date of the project, through support for research projects with a maximum duration of 24 months to be started in 2023, whose results are expected to benefit (broadly intended) the Province of Trento. We are looking for a young researcher below the age of 35, already in possession of a PhD, and with an excellent research track in cosmology and gravitation broadly intended, with a broad profile at the interface of theory and data, and experience in tests of fundamental physics from cosmological and astrophysical data. If you are interested, please send us an expression of interest following the indications provided in our INSPIRE job ad (with material preferably sent to this AJO eDelivery link - note that there are several stages of selection, please see towards the end of the INSPIRE job ad for more details): please get in touch if you are interested!
Physics Frontiers Random Questions interview on YouTube
The Random Questions video interview associated to the Physics Frontiers podcast episode on my primordial graviton background paper, which I previously reported on in an earlier news item, has now been published on YouTube. You can find it here, where you can listen to Jim and I discuss a few (truly) random things, from the way I get my ideas, to my career, to culture shock, and so on. I hope you will enjoy it!
Asteroid precession and fifth forces paper accepted in JCAP!
My paper with Yu-Dai Tsai, Youjia Wu, and Luca Visinelli, where we use asteroids as a probe of fifth forces, including those mediated by new ultralight particles which could be the dark matter, has been accepted for publication in JCAP! We find that we can potentially set some of the leading fifth force constraints in a certain range of mediator mass. This is another paper which has gone through a really long journey, as it was conceived during a brainstorm Zoom call in October 2020. We are now developing a number of follow-up ideas with asteroid experts, so stay tuned for more! You can find the preprint version of the paper on arXiv: 2107.04038.
Teaching starts today!
Today marks the start of the new semester, and with it of my teaching duties. I have a particularly heavy teaching load this semester (as a result of my having started mid-semester in October, which implied I obviously could not teach classes in the previous semester), where I’ll be lecturing General Physics I part 2 (basically Classical Thermodynamics, roughly following Zemansky) for the Mathematics BSc, Advanced Topics in Theoretical Physics (which, despite the cryptic name, is an advanced course in Modern Cosmology, which will more or less cover Chapters 1-8 of Dodelson) for the Physics MSc, as well as within the Percorso di Approfondimento in Fisica (PAF), a supplement lecture series for the Physics BSc aimed towards particularly capable and motivated students. Needless to say, I already know that throughout the semester research will proceed on a very low gear in the best of cases (and I hope my collaborators won’t hate me for this! 😝). However, despite the overall heavy load, I really look forward to teaching and interacting with bright young minds! As an aside, all my teaching material (notes, slides, exams, solutions, and so on) will be available, while being regularly updated, on the English and Italian versions of my teaching page.
