Particle Physics from Stars

TL;DR

This review surveys how hot and dense stellar interiors serve as natural laboratories for weakly interacting low-mass particles, notably neutrinos and axions, by analyzing energy-loss channels, helioseismic data, and SN 1987A neutrino observations. It develops a framework where extra cooling is constrained by simple energy-loss criteria in globular clusters and HB stars, and by the duration and spectrum of SN1987A neutrinos, translating particle couplings into observable stellar features. The work highlights axions as a prime example, detailing limits on axion-photon, axion-electron, and axion-nucleon couplings and discussing their cosmological implications and experimental searches. Overall, stellar-physics constraints complement laboratory experiments and cosmology, with axions remaining a particularly compelling dark-matter candidate and future galactic SN observations poised to refine the bounds further.

Abstract

Low-mass particles such as neutrinos, axions, other Nambu-Goldstone bosons and gravitons are produced in the hot and dense interior of stars. Therefore, astrophysical arguments constrain the properties of these particles in ways which are often complementary to cosmological arguments and to laboratory experiments. This review provides an update on the most important stellar-evolution limits and discusses them in the context of other information from cosmology and laboratory experiments.

Figures (14)

• Figure 1: Primakoff production of axions in the Sun.
• Figure 2: Fractional difference in sound-speed profiles of solar models with axion losses compared to the reference model Schlattl99. The shaded area is the uncertainty of the seismic model Scilla97. The axion-photon coupling constant was $g_{10}$=4.5 (solid line), 10 (short-dashed), 15 (dash-dotted), 20 (dash-dot-dot-dotted).
• Figure 3: Globular cluster M3. (Image courtesy of Palomar/Caltech.)
• Figure 4: Color-magnitude diagram for the globular cluster M3, based on the photometric data of 10,637 stars Buonanno86. Vertically is the brightness in the visual (V) band, horizontally the difference between B (blue) and V brightness, i.e. a measure of the color and thus surface temperature, where blue (hot) stars lie toward the left. The classification for the evolutionary phases is as follows Renzini88. MS (main sequence): core hydrogen burning. BS (blue stragglers). TO (main-sequence turnoff): central hydrogen is exhausted. SGB (subgiant branch): hydrogen burning in a thick shell. RGB (red-giant branch): hydrogen burning in a thin shell with a growing core until helium ignites. HB (horizontal branch): helium burning in the core and hydrogen burning in a shell. AGB (asymptotic giant branch): helium and hydrogen shell burning. P-AGB (post-asymptotic giant branch): final evolution from the AGB to the white-dwarf stage.
• Figure 5: Allowed values for a core-mass excess at helium ignition $\delta{\cal M}_c$ and the envelope helium mass fraction $Y_{\rm env}$ of evolved globular-cluster stars. Left after Raffelt96a, right after Catelan96. The observables are the brightness difference $\Delta M_{\rm HB}^{\rm tip}$ between the HB and the RGB tip, the RR Lyrae mass-to-light ratio $A$, their absolute brightness $M_{\rm RR}$, and the number ratio $R$ between HB and RGB stars.