Neutrino Physics from the Cosmic Microwave Background and Large Scale Structure (1309.5383v3)

Abstract: This is a report on the status and prospects of the quantification of neutrino properties through the cosmological neutrino background for the Cosmic Frontier of the Division of Particles and Fields Community Summer Study long-term planning exercise. Experiments planned and underway are prepared to study the cosmological neutrino background in detail via its influence on distance-redshift relations and the growth of structure. The program for the next decade described in this document, including upcoming spectroscopic galaxy surveys eBOSS and DESI and a new Stage-IV CMB polarization experiment CMB-S4, will achieve sigma(sum m_nu) = 16 meV and sigma(N_eff) = 0.020. Such a mass measurement will produce a high significance detection of non-zero sum m_nu, whose lower bound derived from atmospheric and solar neutrino oscillation data is about 58 meV. If neutrinos have a minimal normal mass hierarchy, this measurement will definitively rule out the inverted neutrino mass hierarchy, shedding light on one of the most puzzling aspects of the Standard Model of particle physics --- the origin of mass. This precise a measurement of N_eff will allow for high sensitivity to any light and dark degrees of freedom produced in the big bang and a precision test of the standard cosmological model prediction that N_eff = 3.046.

• The paper proposes leveraging upcoming CMB polarization and spectroscopic surveys to measure neutrino masses with a precision of 16 meV.
• It demonstrates how neutrino properties affect CMB lensing and LSS power spectra, testing the robustness of the standard cosmological model.
• Findings may reveal deviations in effective neutrino numbers, potentially uncovering sterile neutrinos or other exotic particles.

Overview of Neutrino Physics in Cosmology

The paper "Neutrino Physics from the Cosmic Microwave Background and Large Scale Structure" articulates a systematic exploration of the impact of cosmic neutrinos on cosmological parameters and large scale structures (LSS), exploring the synergy of theoretical predictions and observational constraints. The authors focus on the cosmological inferences of neutrino mass and number density from the Cosmic Microwave Background (CMB) and LSS within the framework of the standard cosmological model.

Neutrinos, CMB, and LSS

Understanding neutrino physics is paramount to advancing knowledge in both cosmology and particle physics. The paper details how neutrinos, despite their negligible cross-section, influence the universe's thermodynamics due to their sheer number. CMB observations have constrained the effective number of neutrinos, $N_{\rm eff}$, to $3.36 \pm 0.34$, a result consistent with the expected three species of light neutrinos, but allowing room for new physics such as sterile neutrinos or other exotic particles.

Measuring Neutrino Masses

The authors propose an ambitious observational program that leverages upcoming CMB polarization experiments like CMB-S4 and spectroscopic surveys such as eBOSS and DESI, aiming to achieve precision measurements of neutrino masses. Specifically, the goal is to limit the sum of neutrino masses, $\sum m_\nu$, to 16 meV, a precision that would be sufficient to distinguish between normal and inverted mass hierarchies. This pursuit would clarify one of the lingering ambiguities in the Standard Model of particle physics concerning the origin of mass.

Implications and Theoretical Considerations

If successful, these measurements could either reinforce the robustness of the current cosmological model or hint at non-standard physics. A $N_{\rm eff}$ value deviating from 3.046 would imply new interactions or particles, fundamentally altering our understanding of the early universe. In this context, neutrino properties uniquely affect both the CMB lensing potential and the LSS power spectrum, offering distinct observational signatures that could differentiate neutrino-induced effects from other cosmological parameters.

Future Prospects

With the anticipated improvements in observational technologies and methodologies, the paper underscores the potential to unearth new physics. The combination of complementary probes offers a promising path to a high-confidence measurement of neutrino masses and effectively testing the hypothesis of extra relativistic species. As experimental capabilities rise, so too will the precision and accuracy of these cosmological tests, potentially opening new avenues in both particle physics and cosmology.

Conclusion

In summary, this paper presents a comprehensive analysis of the role of neutrinos in cosmology, underscoring the pivotal contributions that next-generation CMB and LSS observations can make toward solving critical questions in neutrino physics. By achieving high precision in constraining $\sum m_\nu$ and $N_{\rm eff}$, the outlined research has the potential to profoundly impact our understanding of the universe's fundamental properties and its earliest moments.