BROWSEPOL – Beyond standaRd mOdel With coSmic microwavE background POLarization

30/10/2025 Page maintained by Alessandro Gruppuso - Last updated on 20/11/2025

BROWSEPOL – CUP: C53D23001080006

MUR PRIN2022 Project “BROWSEPOL: Beyond standaRd mOdel With coSmic microwavE background POLarization”-2022EJNZ53 financed by the European Union – Next Generation EU.

Research Units and members

  • University of Padova
    • Prof. N.Bartolo, Principal Investigator
    • Dr. H.V.Ragavendra
  • University of Ferrara
    • Prof. P.Natoli, Associated Investigator
    • Dr. G.Galloni
  • INAF OAS Bologna
    • Dr. A.Gruppuso, Associated Investigator
    • Dr. S.Paradiso

Overview and Goals

Modern cosmology shifted in recent years from early discovery to precision era, turning into a primary test bench for fundamental physics. The Cosmic Microwave Background (CMB) is one of the most powerful cosmological tools: it grants unique access to the early Universe, provides constraints on high energy physics at scales never achievable in earthly facilities, and is an ideal laboratory for stress-tests of scenarios beyond the standard models of cosmology and particle physics.

While in remarkable agreement with the standard Lambda Cold Dark Matter (ΛCDM) model with simple inflationary initial conditions, CMB data display a few intriguing signatures, which have not yet found a self-consistent explanation. Indeed, hints of new physics might have already surfaced. This is the case of parity violation leading to the so-called cosmological birefringence (CB), which causes rotation of linear polarization of propagating photons, breaking Maxwell’s electromagnetism. Since long considered a promising avenue for new physics, CB is nowadays experiencing an intense interest, after hints of detection on Planck legacy data at > 99% significance.

In addition, “anomalies” in CMB data are present especially at large angular scales. They have been explored extensively in the CMB temperature (T) field, but no convincing conclusion about their nature, whether primordial, due to systematics or simply to a statistical fluke, could be reached. Forthcoming high quality polarization data provide an unmissable opportunity to resolve both conundrums, shedding new light into the physics of both the early and the late-time Universe.

Such observations are highly motivated by the quest for polarization B modes, a unique tracer of primordial gravitational waves (PGW) from inflation. However, there is much more in CMB polarization, and B modes in particular, than this very important goal. Cross-correlations of B-modes with CMB T and E modes are an almost exclusive tracer of parity violation, and B-modes can also be a potential tracer of physics beyond the standard model for anomalies, complementing T and E information.

We plan to pursue these clues, by developing an integrated effort that starts from the definition of the most intriguing theoretical scenarios and moves on through the set-up of new, robust and efficient estimators which credibly account for the major contaminants expected from foreground emission and instrumental systematics. We aim at a thorough exploitation of legacy data, from Planck and WMAP, as well as to forecasting the performance of next-generation experiments, including LiteBIRD, with a credible goal to improve on their design. BROWSEPOL will deliver a realistic assessment of how future CMB experiments can disentangle B modes generated by standard inflation from intriguing signatures of new physics, so it will also be relevant to exclude that their awaited detection is driven by other effects than PGW in the standard scenario.

Meetings

 

Presentations

  • A.Gruppuso, “Constraining Cosmic Birefringence with CMB data”, Hot Topics in Modern Cosmology, Spontaneous Workshop XVI, Cargese – Insitut d’Etudes Scientifiques de Cargese, 1-7 September 2024.
  • S. Paradiso, “Hints of new physics from CMB polarisation data”, Hot Topics in Modern Cosmology, Spontaneous Workshop XVII, Cargese – Insitut d’Etudes Scientifiques de Cargese, 23-29 March 2025.
  • S.S.Sirletti, “Testing the harmonic-scale dependence of the isotropic cosmic birefringence effect with Planck data”, IAS Princeton, group meeting (Prof. Zaldarriaga). 12 May 2025
  • S.Paradiso, “Investigating parity violation with the polarization of the CMB”, XI meeting on fundamental cosmology – Santander, 17-20 November 2025.
  • S.S.Sirletti, “Testing the harmonic-scale dependence of the isotropic cosmic birefringence effect with Planck data”, Parity Violation from Home Conference. 18-21 November 2025
  • H.V.Ragavendra, “Probing primordial parity-violation using scalar-induced gravitational waves”, Parity Violation from Home Conference. 18-21 November 2025

 

Project Outcomes

  1. A new solution for the observed isotropic cosmic birefringence angle and its implications for the anisotropic counterpart through a Boltzmann approach Alessandro Greco, Nicola Bartolo, Alessandro Gruppuso e-Print: 2401.07079 [astro-ph.CO], DOI: 10.1088/1475-7516/2024/10/028 Published in: JCAP 10 (2024), 028
  2. Planck constraints on cosmic birefringence and its cross-correlation with the CMB G. Zagatti, M. Bortolami, A. Gruppuso, P. Natoli, L. Pagano, G. Fabbian e-Print: 2401.11973 [astro-ph.CO], DOI: 10.1088/1475-7516/2024/05/034 Published in: JCAP 05 (2024), 034
  3. Conversations in the dark: cross-correlating birefringence and LSS to constrain axions S. Arcari, N. Bartolo, A. Greco, A. Gruppuso, M. Lattanzi, P. Natoli e-Print: 2407.02144 [astro-ph.CO], DOI: 10.1088/1475-7516/2024/10/101 Published in: JCAP 10 (2024), 101
  4. Breaking parity: the case of the trispectrum from chiral scalar-tensor theories of gravity Tommaso Moretti,  Nicola Bartolo, Alessandro Greco Published in: JCAP 07 (2025) 051 e-Print: 2410.11801 [astro-ph.CO]
  5. Cosmic Polarization Rotation from CMB data: A review for GR 110 Published in: Int.J.Mod.Phys.D 34 (2025) 03, 2540008 e-Print: 2502.07743 [astro-ph.CO] Alessandro Gruppuso Sperello di Serego Alighieri 
  6. LiteBIRD science goals and forecasts: constraining isotropic cosmic birefringence LiteBIRD Collaboration • E. de la Hoz et al. e-Print: 2503.22322 [astro-ph.CO], DOI: 10.1088/1475-7516/2025/07/083 Published in: JCAP 07 (2025), 083
  7. Twisted echoes of an odd quartet: Scalar-induced gravitational waves as a probe of primordial parity-violation H.V. Ragavendra, Nicola Bartolo e-Print: 2507.02733 [astro-ph.CO], submitted
  8. Planck constraints on the scale dependence of isotropic cosmic birefringence M. Ballardini, A. Gruppuso, S. Paradiso, S.S. Sirletti, P. Natoli e-Print: 2507.16714 [astro-ph.CO], DOI: 10.1088/1475-7516/2025/09/075 Published in: JCAP 09 (2025), 075
  9. LiteBIRD Science Goals and Forecasts. $E$-mode Anomalies LiteBIRD Collaboration • A.J. Banday et al. e-Print: 2508.16451 [astro-ph.CO], submitted to JCAP
  10. Stairway to Axions: the cross-correlation of birefringence and galaxies from NPIPE and Quaia S. Arcari, N. Bartolo, G. Fabbian, A. Greco, A. Gruppuso, M. Lattanzi, P. Natoli, L. Pagano, G. Zagatti e-Print: 2509.22273 [astro-ph.CO], submitted to JCAP
  11. The first data-driven bounds on the quantum decoherence of inflationary gravitational waves Jessie de Kruijf, Giacomo Galloni, Nicola Bartolo e-Print: 2511.14727 [astro-ph.CO], submitted