2023 CAP Congress / Congrès de l'ACP 2023

Probing Physics Beyond the Standard Model: Limits from BBN and the CMB Independently and Combined

22 Jun 2023, 09:00

15m

UNB Kinesiology (Rm. 214 (max. 60))

Oral (Non-Student) / Orale (non-étudiant(e)) Particle Physics / Physique des particules (PPD) (PPD) R1-1 DM / Neutrino 5 | DM / Neutrino 5 (PPD)

Speaker

Dr Tsung-Han Yeh (TRIUMF)

Description

We present new Big Bang Nucleosynthesis (BBN) limits on the cosmic expansion rate or relativistic energy density, quantified via the number $N_{\nu }$ of equivalent neutrino species. We use the latest light element observations, neutron mean lifetime, and update our evaluation for the nuclear rates d + d → ${}^3$He + n and d + d → ${}^3$H + p. Combining this result with the independent constraints from the cosmic microwave background (CMB) yields tight limits on new physics that perturbs $N_{\nu }$ and the baryon-to-photon ratio $\eta$ prior to cosmic nucleosynthesis: a joint BBN+CMB analysis gives $N_{\nu }$ = 2.898 ± 0.141, resulting in $N_{\nu }$ < 3.180 at 2$\sigma$. The strength of the independent BBN and CMB constraints now opens a new window: we can search for limits on potential changes in $N_{\nu }$ and/or $\eta$ between the two epochs. The present data place strong constraints on the allowed changes in $N_{\nu }$ between BBN and CMB decoupling; for example, we find -0.708 $

Presentation materials

2023_CAP_Congress_Tsung-Han_Yeh.pdf