Cool WISPs for stellar cooling excesses

Abstract

Several stellar systems (white dwarfs, red giants, horizontal branch stars and possibly the neutron star in the supernova remnant Cassiopeia A) show a mild preference for a non-standard cooling mechanism when compared with theoretical models. This exotic cooling could be provided by Weakly Interacting Slim Particles (WISPs), produced in the hot cores and abandoning the star unimpeded, contributing directly to the energy loss. Taken individually, these excesses do not show a strong statistical weight. However, if one mechanism could consistently explain several of them, the hint could be significant. We analyze the hints in terms of neutrino anomalous magnetic moments, minicharged particles, hidden photons and axion-like particles (ALPs). Among them, the ALP or a massless HP represent the best solution. Interestingly, the hinted ALP parameter space is accessible to the next generation proposed ALP searches, such as ALPS II and IAXO and the massless HP requires a multi TeV energy scale of new physics that might be accessible at the LHC. arXiv:1512.08108v2 [astro-ph.HE]

GAMBIT and its application in the search for physics Beyond the Standard Model

“…Axions are an intriguing theoretical possibility due to their ability to solve the strong-CP problem of the SM whilst providing a credible DM candidate [332][333][334][335]. One can also use axion-like particles to reconcile various tensions between astrophysical observations and theory, including the cooling of white dwarfs [336][337][338][339][340][341][342], and the transparency of the Universe to gamma rays [343][344][345][346][347][348].…”

A minimal scale invariant axion solution to the strong CP-problem

“…All astrophysical bounds dealing with the axion-photon conversion (cooling of stars [44]) are relevant for the discussed model as well. Future experiments searching for solar axion emission [45,46], and for the light shining through the wall [47], are expected to put stronger constraints on the QCD axion parameters even if it does not contribute to the dark matter.…”

IAXO, next-generation of helioscopes

“…More intriguingly, several independent observations of the cooling of different stellar systems seem to agree with the need for a novel cooling mechanism, such as the one provided by axions or ALPs, in addition to the standard astrophysical processes (see M.Giannotti's contribution to these proceedings). Though this is still only a speculative hypothesis, it is remarkable that axions or ALPs are unique, among the several weakly interactive particle candidates, in their ability to explain all the independent observations [15].…”

“…Besides particle physics, axions and ALPs may play a fundamental role in astrophysics and cosmology. In particular, they are excellent candidates for the cold dark matter in the universe [11,12,13,14] and could explain the anomalous cooling of several stellar systems [15], the seeming transparency of the universe to very high energy (TeV) gamma rays in the galactic and extragalactic medium [16], some anomalous redshift-dependence of AGN gamma-ray spectra [17] and, perhaps, anomalous x-ray observations of the active Sun [18].…”