Low energy antideuterons: shedding light on dark matter

TL;DR

Low-energy antideuterons offer a unique indirect DM probe due to suppressed astrophysical backgrounds at $T_{\overline{D}} \lesssim 1$ GeV. The authors compute primary ${\overline{D}}$ fluxes from DM annihilation in SUSY, universal extra dimensions (UED) LKPs, and warped GUT scenarios, using a coalescence model with $p_0=58$ MeV/$c$ and a diffusion+solar modulation framework anchored to a contracted N03 halo with local density ${\rho^{\rm loc}_{\rm DM}} \simeq 0.38$ GeV/cm$^3$. They re-evaluate the secondary/tertiary background, showing a non-negligible low-energy component that weakens AMS-02 prospects but leaves balloon-based GAPS largely background-free and satellite GAPS capable of probing the full UED parameter space, depending on solar modulation. The study highlights the complementarity of antideuteron searches with direct detection and neutrino telescopes, and emphasizes that the dominant uncertainties arise from hadronic coalescence, Galactic propagation, halo structure, and clumpiness, with total primary flux uncertainties potentially spanning up to two orders of magnitude.

Abstract

Low energy antideuterons suffer a very low secondary and tertiary astrophysical background, while they can be abundantly synthesized in dark matter pair annihilations, therefore providing a privileged indirect dark matter detection technique. The recent publication of the first upper limit on the low energy antideuteron flux by the BESS collaboration, a new evaluation of the standard astrophysical background, and remarkable progresses in the development of a dedicated experiment, GAPS, motivate a new and accurate analysis of the antideuteron flux expected in particle dark matter models. To this extent, we consider here supersymmetric, universal extra-dimensions (UED) Kaluza-Klein and warped extra-dimensional dark matter models, and assess both the prospects for antideuteron detection as well as the various related sources of uncertainties. The GAPS experiment, even in a preliminary balloon-borne setup, will explore many supersymmetric configurations, and, eventually, in its final space-borne configuration, will be sensitive to primary antideuterons over the whole cosmologically allowed UED parameter space, providing a search technique which is highly complementary with other direct and indirect dark matter detection experiments.

Figures (7)

• Figure 1: A conceptual outline of how to compute the antideuteron flux induced by a dark matter particle ($\chi$) pair annihilation. First, the dark matter particle physics model provides the pair annihilation cross section into standard model particles ( e.g. a quark-antiquark pair, gauge and/or Higgs bosons etc.). Then, a Monte Carlo hadronization simulation translates the elementary particle output into the flux of antiprotons and antineutrons. Finally, a nuclear physics model (in the present case the coalescence model) provides the final yield of antideuterons.
• Figure 2: Differential antideuteron flux from four different WIMP models, as a function of the antideuterons' kinetic energy per nucleon. The solid black line corresponds to a WIMP with mass 100 GeV annihilating with BR=1 into a $b\bar{b}$ pair, the red dotted line to a 1000 GeV WIMP annihilating with BR=1 into $W^+W^-$ pairs, the green dot-dashed line to a 500 GeV $B^{(1)}$ (the Kaluza-Klein first excitation of the hypercharge gauge boson), LKP in the UED scenario, while the blue dashed line to a LZP particle pair annihilating dominantly through the $Z$$s$-channel resonance, with a mass of 40 GeV. The shaded regions correspond to the sensitivities of various existing and proposed experiments featuring antideuteron searches.
• Figure 3: The sensitivity reach of antideuteron search experiments for WIMP pairs annihilating with BR=1 into $b\bar{b}$ pairs (left panel) and $W^+W^-$ pairs (right panel), in the plane defined by the particle mass $m_\chi$ and by the factor ${\langle\sigma v\rangle_0}/m_\chi^2$. The black solid line gives the experimental upper limit on the antideuteron flux from BESSFuke:2005it. For future experiments, the lines correspond to the critical primary antideuteron flux giving an expected number of detected antideuterons over the full lifetime of the experiment equal to 1. The red dashed line sketches the projected sensitivity of the AMS-02 experiment after 3 years of data taking. The fainter line corresponds to the detection threshold of 1 primary ${\overline{D}}$, while the thicker line to a number of primary ${\overline{D}}$s sufficient to disentangle them from the background. The magenta double-dotted-dashed lines indicate the sensitivity of a balloon-borne GAPS setup in a LDB mission over Antarctica (upper line) and in a ULDB mission over Australia (lower line). The sensitivity of a satellite-borne and interplanetary probe version of GAPS are instead indicated by a dot-dashed green line. Again, the fainter lines correspond to the detection threshold of 1 primary ${\overline{D}}$, while the thicker ones to a number of primary ${\overline{D}}$s sufficient to disentangle them from the background. The upper and lower blue lines correspond to the bounds from the measured flux of positrons and antiprotons, respectively. Points on the plot above the dotted lines give a total $\chi^2$ for the background plus primary component which is excluded at 95% C.L., while for points above the solid lines, the positron/antiproton fluxes induced by WIMP annihilations only (primaries) exceed, at the 2-$\sigma$ level, the experimentally measured flux in at least one energy bin. Finally, the orange-shaded region corresponds to supersymmetric models giving a WMAP relic abundance within 2-$\sigma$, while the yellow shaded area corresponds to the maximal region spanned by supersymmetric models in the $(m_\chi,{\langle\sigma v\rangle_0}/m_\chi^2)$ plane (see Ref. Profumo:2005xd). As a guideline, we also indicate the "naive" cross section range favored by the WMAP deduced CDM abundance according to the relation given in Eq. (\ref{['eq:naivesv']}).
• Figure 4: The sensitivity reach of antideuteron search experiments for two extra-dimensional DM models: the UED model, with a $B^{(1)}$ LKP (left panel) and the warped extra-dimensional GUT scenario of Ref. Agashe:2004ciAgashe:2004bmHooper:2005fj, featuring a right-handed neutrino as the LZP, in the mass range where the LZP resonantly annihilates into the $Z$ gauge boson (right panel). The conventions for the various lines are the same as in Fig. \ref{['fig:susy']}. In the UED case (left), we indicate with a dotted black line the pair annihilation cross section of the LKP as a function of the mass, and shade in green the most conservative mass range where the LKP might give the WMAP inferred CDM abundance within 2-$\sigma$. In the right panel, the green shaded area corresponds to LZP realizations giving a relic abundance consistent with the upper limit on the CDM abundance.
• Figure 5: ( Left panel): The correlation between the expected sensitivity of antideuteron searches and of direct detection experiments for supersymmetric models giving a thermal neutralino relic abundance in the WMAP range. On the $y$ axis we indicate the ratio of the neutralino-proton spin-independent scattering cross section over the projected maximal sensitivity of the CDMS-II experiment, at the WIMP mass corresponding to the neutralino mass for the model under consideration. On the $x$ axis we indicate the number of expected primary antideuterons detected at the ULDB GAPS mission (ratio of the average flux over the experimental sensitivity). ( Right panel): the same as in the left panel, but correlating the sensitivity of antideuteron searches at GAPS on a ULDB mission with that IceCube for the neutralino-annihilation induced flux of muons from the center of the Sun.