Powerful solar signatures of long-lived dark mediators

105

Dark matter particles will be captured in neutron stars if they undergo scattering interactions with nucleons or leptons. These collisions transfer the dark matter kinetic energy to the star, resulting in appreciable heating that is potentially observable by forthcoming infrared telescopes. While previous work considered scattering only on nucleons, neutron stars contain small abundances of other particle species, including electrons and muons. We perform a detailed analysis of the neutron star kinetic heating constraints on leptophilic dark matter. We also estimate the size of loop induced couplings to quarks, arising from the exchange of photons and Z bosons. Despite having relatively small lepton abundances, we find that an observation of an old, cold, neutron star would provide very strong limits on dark matter interactions with leptons, with the greatest reach arising from scattering off muons. The projected sensitivity is orders of magnitude more powerful than current dark matter-electron scattering bounds from terrestrial direct detection experiments.Neutron stars provide particularly powerful DM constraints, because their high density leads to efficient capture. Indeed, for DM-nucleon cross sections above a threshold value of order 10 −45 cm 2 , the capture probably saturates at the geometric limit, σ ∼ πR 2 * m n /M * , such that all dark matter incident on the star is captured. This conclusion holds irrespective of whether DM scattering interactions are spin independent (SI) or spin dependent (SD). Given that conventional direct detection experiments currently have sensitivity to DM-nucleon cross sections below 10 −45 cm 2 only in a limited DM mass range, and only for SI interactions, NS techniques are clearly very useful. Moreover, velocity or momentum dependent interactions are completely inaccessible to terrestrial direct detection experiments, being severely suppressed in the non-relativistic regime applicable for scattering on Earth. In comparison, DM particles are accelerated to quasi-relativistic velocities upon NS infall, effectively erasing such kinematic suppression.When dark matter is gravitationally captured by a NS, the kinetic energy transferred in the collisions heat up the star. The captured dark matter will then undergo a series of further collisions, eventually transferring almost all of its initial kinetic energy, to reach a state of thermal equilibrium with the star. As shown in Refs. [18,19] this can heat neutron stars up to 1700K. 1 Because old isolated neutron stars can cool to temperatures below 1000K, such heating (or its absence) can be used to place limits on the strength of dark matter interactions. 2 Importantly, this kinetic heating may be within reach of forthcoming infrared telescopes [18,19]. Provided NSs are nearby, faint and sufficiently isolated, they are likely to be discovered by existing radio telescopes such as the Fivehundred-meter Aperture Spherical radio Telescope (FAST) [37], or the future Square Kilometer Array (SKA) [38]. Their thermal emission can then be m...

Section: Introductionmentioning

confidence: 99%

Capture of leptophilic dark matter in neutron stars

Bell

Busoni

Robles

2019

105

“…Other limits come from ref. [32] where both gamma ray and neutrino signals are considered, Table 1. Parameters used in our analysis to describe the spectra of neutrinos and gamma rays from long-lived mediator decays.…”

Section: Introductionmentioning

confidence: 99%

Neutrinos and gamma rays from long-lived mediator decays in the Sun

Niblaeus

Beniwal

Edsjö

2019

We investigate a scenario where dark matter (DM) particles can be captured and accumulate in the Sun, and subsequently annihilate into a pair of long-lived mediators. These mediators can decay further out in the Sun or outside of the Sun. Compared to the standard scenario where DM particles annihilate directly into Standard Model particles close to the solar core, here we also obtain fluxes of gamma rays and charged cosmic rays. We simulate this scenario using a full three-dimensional model of the Sun, and include interactions and neutrino oscillations. In particular, we perform a model-independent study of the complementarity between neutrino and gamma ray fluxes by comparing the recent searches from IceCube, Super-Kamiokande, Fermi-LAT, ARGO and HAWC.We find that the resulting neutrino fluxes are significantly higher at high energy when the mediators decay further out in the Sun. We also find that gamma ray searches place stronger constraints than neutrino searches on these models even in cases where the mediators decay mainly inside the Sun, except in the approximately inner 10% of the Sun where neutrino searches are more powerful. We present our results in a model-independent manner and release a new version of the WimpSim code that can be used to simulate this scenario for arbitrary mediator models.

“…Of course, directly measuring the DM annihilation rate in the Sun (Earth) is possible only if some of the annihilation products are sufficiently weakly interacting to escape the Sun (Earth). Wellestablished search strategies rely on the neutrinos produced by annihilations into Standard Model (SM) final states [11][12][13][14][15][16][17][18], while in multi-state dark sectors long-lived dark states could also furnish this role [19][20][21][22][23][24][25][26][27][28][29]. Such multi-state dark sectors are often proposed in order to realize strong DM self-interactions, and are especially well-motivated in this context.…”

Section: Introductionmentioning

confidence: 99%

A solar system test of self-interacting dark matter

Gaidau

Shelton

2019

Dark matter (DM) self-interactions affect the gravitational capture of DM in the Sun and Earth differently as a simple consequence of the differing kinematics of collisions within the two potential wells: the dominant effect of self-interactions in the Sun is to provide an additional channel for capture, while the dominant effect in the Earth is to eject previously captured DM. We point out that this simple observation can be used to deduce the existence of DM self-interactions by comparing the annihilation rates of DM gravitationally bound within the Sun and Earth. We compute the Sun and Earth annihilation fluxes for DM with spin-independent nuclear cross-sections and thermal annihilation crosssections and demonstrate that, for cross-sections allowed by direct detection, self-interactions can easily suppress the expected Earth flux by multiple orders of magnitude. This suppression is potentially significant even for self-interaction cross-sections orders of magnitude below the Bullet Cluster bounds, making this solar system comparison a leading test of dark matter self-interactions. Additionally, we consider thermalization of the captured DM population with the nuclei of the capturing body in some detail, accounting for both nuclear and selfinteractions, and point out some consequential and broadly applicable considerations.