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 One of my next tasks will be to update the group’s website, which is chronically out-of-date.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!
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.
Inflationary gravitational waves and PTA paper published in JHEAp!
My single-author paper studying an inflationary interpretation of the signal observed by PTA experiments, which I previously reported on in an earlier news item, has now officially been published in JHEAp! The full bibliographic coordinates for the paper are JHEAp 39 (2023) 81. Here is a link to the paper.
Visit by Anish Ghoshal
This week we have Anish Ghoshal, currently a postdoc at the University of Warsaw, visiting us for a couple of days. Anish is visiting to work on a couple of projects both with me and Max Rinaldi, respectively on novel dark matter production mechanisms, and inflation. Welcome Anish!
Inflationary gravitational waves and PTA paper accepted in JHEAp!
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.
Primordial graviton background paper published in ApJ Letters!
My paper with Avi Loeb on the primordial graviton background, which I previously reported on in an earlier news item, has now officially been published in ApJ Letters! The full bibliographic coordinates for the paper are Astrophys. J. Lett. 939 (2022) L22. Here is a link to the paper (which is published Open Access).
Primordial graviton background paper accepted in ApJ Letters!
My latest paper with Avi Loeb has just been accepted for publication in ApJ Letters! I can confidently say that is at the same time one of the simplest yet most exciting papers I have ever written (Avi is really good at coming up with simple yet profound ideas, and I won’t lie, the idea behind this paper is entirely his). The short idea is that one can (with some caveats) rule out the whole inflationary paradigm, without reference to any specific model, by finding a background of relic gravitons with certain specific properties, the reason being that inflation should have washed it out: we show that this will be extremely challenging, but not impossible (I will likely have retired by the time it will even be possible). You can find the preprint version of the paper, which is also the first one I have written with my new Trento affiliation, on arXiv: 2208.14088.
