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Dark Matter, Baryon Number, and Cosmic-Ray Antinuclei

Caleb Gemmell, Dan Hooper, Seth Koren, Fabrizio Vassallo

Abstract

Antideuterons and antihelium nuclei in the cosmic-ray spectrum have long been considered a smoking gun signature of dark matter annihilation, making the tentative observation of several such events by AMS highly intriguing. Conventional dark matter models, however, can produce only up to O(1) antideuteron events at AMS and are not capable of generating observable fluxes of antihelium. In this letter, we propose a class of models in which dark matter annihilates into particles carrying baryon and lepton number, whose subsequent decays produce enhanced fluxes of antinucleons and antinuclei. Such scenarios are motivated by Grand Unified Theories and can lead to an order-of-magnitude or larger enhancement in the resulting antideuteron and antihelium-3 fluxes, providing a means by which to potentially explain the events reported by the AMS Collaboration.

Dark Matter, Baryon Number, and Cosmic-Ray Antinuclei

Abstract

Antideuterons and antihelium nuclei in the cosmic-ray spectrum have long been considered a smoking gun signature of dark matter annihilation, making the tentative observation of several such events by AMS highly intriguing. Conventional dark matter models, however, can produce only up to O(1) antideuteron events at AMS and are not capable of generating observable fluxes of antihelium. In this letter, we propose a class of models in which dark matter annihilates into particles carrying baryon and lepton number, whose subsequent decays produce enhanced fluxes of antinucleons and antinuclei. Such scenarios are motivated by Grand Unified Theories and can lead to an order-of-magnitude or larger enhancement in the resulting antideuteron and antihelium-3 fluxes, providing a means by which to potentially explain the events reported by the AMS Collaboration.
Paper Structure (3 sections, 2 equations, 6 figures)

This paper contains 3 sections, 2 equations, 6 figures.

Table of Contents

  1. Average Antinucleon Yields per Dark Matter Annihilation
  2. Antinuclei Yields for Models with Various Baryon and Lepton Numbers
  3. Antinuclei Yields for Alternative Hadronic Decay Channels

Figures (6)

  • Figure 1: In the models considered in this letter, the dark matter annihilates to a pair of scalars with baryon and lepton number, $\chi \chi \rightarrow \phi_{i,j} \, \bar{\phi}_{i,j}$, where $i$ and $j$ denote the baryon and lepton number of the particle, respectively. These scalars then decay as shown here, for the cases of the models with $B=L=1$ (left) and $B=L=3$ (right).
  • Figure 2: The average number of antideuterons (top) and antihelium-3 nuclei (bottom) per dark matter annihilation event in our models with $B=L=1$ or $B=L=3$ as a function of the mass of the decaying scalar, $m_{\phi}$. These results are compared to the yields predicted for $50$ GeV dark matter particles annihilating directly to $b\bar{b}$ (dashed line). The multiplicities of antideuterons and antihelium nuclei produced through dark matter annihilation can be enhanced by more an order of magnitude in the $B=L=3$ model, especially for small values of $m_{\phi}$. Note that in the $B=L=1$ model, the number of predicted antihelium events is below the range shown in this figure.
  • Figure 3: The ratio of antideuterons (top) and antihelium-3 nuclei (bottom) to antinucleons produced through dark matter annihilation in our models with $B=L=1$ or $B=L=3$ as a function of the mass of the decaying scalar, $m_{\phi}$. These results are compared to the yields predicted for $50$ GeV dark matter particles annihilating directly to $b\bar{b}$ (dashed line). The relative multiplicities of antideuterons and antihelium nuclei produced through dark matter annihilation can be enhanced by more than an order of magnitude in the $B=L=3$ model, especially for small values of $m_{\phi}$. Note that in the $B=L=1$ model, the number of predicted antihelium events is below the range shown in this figure.
  • Figure S1: The average number of antinucleons predicted per dark matter annihilation event in our models with $B=L=1$ or $B=L=3$ as a function of the mass of the decaying scalar, $m_{\phi}$. These results are compared to the yields predicted for $50$ GeV dark matter particles annihilating directly to $b\bar{b}$ (dashed line).
  • Figure S2: As in Figs. \ref{['fig:antinuclei']} and \ref{['fig:antiprotons']}, we plot the average antinuclei yield (left) and antinuclei-to-antinucleon ratios (right), for models in which the scalar $\phi$ carries different values of baryon and lepton number, up to $B = L = 6$.
  • ...and 1 more figures