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Register a new userNew Constraints on Millicharged Particles from Cosmic-ray Production
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We study the production of exotic millicharged particles (MCPs) from cosmic ray-atmosphere collisions which constitutes a permanent MCP production source for all terrestrial experiments Our calculation of the MCP flux can be used to reinterpret existing limits from experiments such as MACRO and Majorana on an ambient flux of ionizing particles. Large-scale underground neutrino detectors are particularly favorable targets for the resulting MCPs. Using available data from the Super-K experiment, we set new limits on MCPs, which are the best in sensitivity reach for the mass range $0.1 lesssim m_{chi} lesssim 0.5$ GeV, and which are competitive with accelerator-based searches for masses up to 1.5 GeV. Applying these constraints to models where a sub-dominant component of dark matter (DM) is fractionally charged allows us to probe parts of the parameter space that are challenging for conventional direct-detection DM experiments, independently of any assumptions about the DM abundance. These results can be further improved with the next generation of large-scale neutrino detectors.
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Millicharged particles (mCPs) are hypothesized particles possessing an electric charge that is a fraction of the charge of the electron. We report a search for mCPs with charges $gtrsim 10^{-4}~e$ that improves sensitivity to their abundance in matter by roughly two orders of magnitude relative to previous searches. This search is sensitive to such particles over a wide range of masses and charges for which they can form stable bound states with matter, corresponding to a gap in parameter space that is beyond the reach of previous searches from accelerators, colliders, cosmic-ray experiments, and cosmological constraints.
Axion couplings to photons could induce photon-axion conversion in the presence of magnetic fields in the Universe. The conversion could impact various cosmic distance measurements such as luminosity distances to type Ia supernovae and angular distances to galaxy clusters in different ways. We consider different combinations of the most updated distance measurements to constrain the axion-photon coupling. Ignoring the conversion in intracluster medium (ICM), we find the upper bounds on axion-photon couplings to be around $5 times 10^{-12}$ (nG/$B$) GeV$^{-1}$ for axion mass below $5 times 10^{-13}$ eV, where $B$ is the strength of the magnetic field in the intergalactic medium (IGM). When including the conversion in ICM, the upper bound gets stronger and could reach $5 times 10^{-13} $GeV$^{-1}$ for $m_a < 5 times 10^{-12}$ eV. While this stronger bound moderately depends on the ICM modeling, it is independent of the IGM parameters. All the bounds are determined by the shape of Hubble rate as a function of redshift reconstructable from various distance measurements, and insensitive to todays Hubble rate, of which there is a tension between early and late cosmological measurements. As an appendix, we discuss model building challenges to use photon-axion conversion to make type Ia supernovae brighter to alleviate the Hubble problem/crisis.
We identify potentially the worlds most sensitive location to search for millicharged particles in the 10 MeV to 100 GeV mass range: the forward region at the LHC. We propose constructing a scintillator-based experiment, FORward MicrOcharge SeArch (FORMOSA) in this location, and estimate the corresponding sensitivity projection. We show that FORMOSA can discover millicharged particles in a large and unexplored parameter space, and study strongly interacting dark matter that cannot be detected by ground-based direct-detection experiments. The newly proposed LHC Forward Physics Facility (FPF) provides an ideal structure to host the full FORMOSA experiment.
The Cryogenic Dark Matter Search low ionization threshold experiment (CDMSlite) achieved efficient detection of very small recoil energies in its germanium target, resulting in sensitivity to Lightly Ionizing Particles (LIPs) in a previously unexplored region of charge, mass, and velocity parameter space. We report first direct-detection limits calculated using the optimum interval method on the vertical intensity of cosmogenically-produced LIPs with an electric charge smaller than $e/(3times10^5$), as well as the strongest limits for charge $leq e/160$, with a minimum vertical intensity of $1.36times10^{-7}$,cm$^{-2}$s$^{-1}$sr$^{-1}$ at charge $e/160$. These results apply over a wide range of LIP masses (5,MeV/$c^2$ to 100,TeV/$c^2$) and cover a wide range of $betagamma$ values (0.1 -- $10^6$), thus excluding non-relativistic LIPs with $betagamma$ as small as 0.1 for the first time.
We update the globular cluster bound on massive ($m_a$ up to a few 100 keV) axion-like particles (ALP) interacting with photons. The production of such particles in the stellar core is dominated by the Primakoff $gamma + Zeto Ze +a$ and by the photon coalescence process $gamma+gammato a$. The latter, which is predominant at high masses, was not included in previous estimations. Furthermore, we account for the possibility that axions decay inside the stellar core, a non-negligible effect at the masses and couplings we are considering here. Consequently, our result modifies considerably the previous constraint, especially for $m_a gtrsim 50$ keV. The combined constraints from Globular Cluster stars, SN 1987A, and beam-dump experiments leave a small triangularly shaped region open in the parameter space around $m_a sim 0.5-1,$ MeV and $g_{agamma} sim 10^{-5}$ GeV$^{-1}$. This is informally known as the ALP cosmological triangle since it can be excluded only using standard cosmological arguments. As we shall mention, however, there are viable cosmological models that are compatible with axion-like particles with parameters in such region. We also discuss possibilities to explore the cosmological triangle experimentally in upcoming accelerator experiments.
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