Dark Matter, Baryon Number, and Cosmic-Ray Antinuclei

Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: I'm Vera.

Jocelyn: And I'm Jocelyn, here with Subrahmanyan.

Vera: We're looking at the paper: "Dark Matter, Baryon Number, and Cosmic-Ray Antinuclei".

Jocelyn: Here's the gist of the paper. Dark matter annihilation into particles carrying baryon and lepton number can produce enhanced fluxes of antinucleons and antinuclei, potentially explaining observations reported by AMS.

Vera: Model Proposal The authors propose a class of models where dark matter annihilates into particles that carry baryon number, guaranteeing the production of antibaryons and enhancing the yield of antinuclei relative to conventional dark matter scenarios Such models can provide a means of potentially accounting for the events reported by AMS while remaining consistent with existing constraints.

Jocelyn: Dark Matter Annihilation Scenarios The model considers dark matter particles, χ, annihilating into a pair of scalars, ϕϕ, which carry baryon and lepton number and antibaryon and antilepton number, respectively.

Vera: Two representative charge assignments for the scalar are considered: ϕ1,1 with B = 1, L = 1, and ϕ3,3 with B = 3, L = 3.

Title and authors: Vera: So we've talked about the title and authors, and they are diving into this paper called "Dark Matter, Baryon Number, and Cosmic-Ray Antinuclei". They are setting up the stage for what's actually in the research.

Jocelyn: The main point they’re making is that conventional dark matter annihilation models fall short when it comes to producing observable fluxes of antihelium nuclei at AMS.

Subrahmanyan: They introduce a new class of models where dark matter annihilates into particles carrying baryon and lepton number, which fundamentally changes the expected output.

Vera: Essentially, they are proposing that by having these annihilation products carry baryon number, their subsequent decays naturally generate enhanced fluxes of antinucleons and anti-nuclei.

Jocelyn: The paper then breaks down exactly what those particles are: they consider scalars phi eleven with B=one and L=one and phi thirty-three with B=three and L=three <ref:2603.12314#pg2>.

Subrahmanyan: And the decay structure is crucial here; for the B = L = one case, the scalar decays into three quarks and one lepton <ref:2603.12314#pg1>.

Vera: Whereas for the B = L = three case, it involves a more complex decay where three phi eleven scalars are produced first <ref:2603.12314#pg2>.

Jocelyn: They then show how these different assignments lead to different operators in terms of their dimension, like an operator of dimension seven or nineteen for the B = L = three case <ref:2603.12314#pg2>.

Subrahmanyan: That’s a technical detail that connects it to Grand Unified Theories, suggesting this isn't just a random tweak but is tied to some bigger physics framework.

Vera: The paper then moves into the event generation part, starting with calculating the multiplicity of antinuclei produced through dark matter annihilation in these models.

Jocelyn: They begin by sampling quark and lepton energies assuming a flat n-body phase space distribution in the massless-daughter limit to get the initial particles.

Subrahmanyan: Then they use Pythia eight point three one three to simulate parton showering and hadronization, specifically employing the Vincia shower algorithm to include electroweak radiation in their simulations <ref:2603.12314#pg3>.

Vera: And then they implement antinuclei formation using a standard coalescence model where an antinucleus forms if every antinucleon pair in the candidate nucleus satisfies p < p coal and their spatial separation is smaller than d coal.

Jocelyn: That coalescence model is a key step in translating the particle output into the observable cosmic-ray nuclei.

Subrahmanyan: It’s important to note that this calculation relies on assumptions about the initial phase space distribution before we even get to the final hadronization.

Vera: And then they present their results regarding enhancement factors for these models to produce those antihelium-three events reported by AMS <ref:2603.12314#pg1>.

Jocelyn: For the B = L = three model, they found that the number of antideuterons and antihelium nuclei produced is enhanced by a factor of O(ten to one hundred) relative to the benchmark dark matter model <ref:2603.12314#pg3,that the number of antideuterons and antihelium nuclei produced is enhanced by>.

Subrahmanyan: This enhancement comes from two factors: first, the larger number of antibaryons produced because the scalar has a baryon number, and second, the increased number of hadronic jets in that initial phi decay.

Vera: They also highlighted that they are sensitive to the value of m phi, even though the mass of the dark matter particle itself doesn't impact how many antinuclei are produced.

Subrahmanyan: That means smaller values of the scalar mass m phi are favorable for getting those increased fluxes while staying consistent with existing constraints from cosmic-ray antiprotons.

Vera: So, to summarize this part, they’ve shown that these specific baryon and lepton number assignments lead to substantial enhancements in antinuclei production compared to standard expectations.

Jocelyn: It sets up the next part where they discuss how these results are being tested and what limitations exist for their findings.

The paper's summary: Subrahmanyan: Now, let's talk about the paper’s summary of "Dark Matter, Baryon Number, and Cosmic-Ray Antinuclei" and what it actually means for us.

Vera: The authors summarize that they considered models where dark matter annihilates into particles carrying baryon and lepton number. This leads to an enhanced yield of nucleons and antinucleons when those particles decay.

Jocelyn: Specifically, for models with B=L=three or greater, dark matter annihilation can produce significantly larger multiplicities and fluxes of antideuterons and antihelium nuclei compared to conventional dark matter scenarios <ref:2603.12314#pg1>.

Subrahmanyan: This could potentially allow dark matter annihilations to produce many of the cosmic-ray antideuteron and antihelium events that have been provisionally reported by the AMS Collaboration.

Vera: But they also stress that this enhancement needs to be checked against constraints from cosmic-ray antiprotons to see if it holds up.

Jocelyn: They are essentially arguing that this specific class of models provides a pathway to potentially explain those cosmic-ray antideuteron and antihelium events.

Subrahmanyan: It’s not just about the flux; it’s about finding a mechanism that works within the existing constraints from cosmic-ray antiprotons.

Vera: So, the paper is suggesting that these models are a viable way to potentially account for what we are seeing in those cosmic-ray spectra.

Jocelyn: They frame this as an improvement over conventional dark matter models which only predict up to O(one) antideuteron events at AMS and not antihelium <ref:2603.12314#pg1,up to O(1) antideuteron events at AMS and>.

Subrahmanyan: It’s about moving beyond the limitations of those simpler models and proposing a richer annihilation process.

Vera: It’s a step toward connecting high-energy physics theories like Grand Unified Theories with observable cosmic ray data.

Jocelyn: And they are pointing out that as AMS-two collects more data, our understanding of antinuclei in the cosmic-ray spectrum is going to improve substantially over the next few years <ref:2603.12314#pg1,in the cosmic-ray spectrum>.

The paper's improvements: Vera: Let's look at how the authors suggest improving their approach in this paper and what those changes imply for future work.

Jocelyn: One improvement they suggest is exploring the parameter space by analyzing figures like Figure S1 and S2 to find optimal dark matter scalar masses m phi that maximize the number of produced antinucleons for a given baryon and lepton number assignment.

Subrahmanyan: That’s useful because it means we can narrow down where to look in the parameter space for the best results based on which assignments you are testing.

Vera: And they also show that by considering different decay channels, like comparing phi to (n nu e)(n nu e)(n nu e) versus phi to (p e+)(p e+)(n nu e).

Jocelyn: The paper suggests that the flux of 3He would be maximized for the first decay channel, phi to (n nu e)(n nu e)(n nu e), especially in the limit of small m phi <ref:2603.12314#pg1>.

Subrahmanyan: That implies that if we want to maximize those specific nuclei, we should focus our search on that particular decay mode when m phi is small.

Vera: And they also note that for larger masses, the two decay channels asymptote to the same rate, so you don't need to worry about which one you pick for high mass scenarios.

Jocelyn: This helps simplify the search by showing that there’s a consistent behavior across different mass ranges when m phi gets larger.

Subrahmanyan: And they also emphasize that they are comparing their results to the yields predicted for fifty GeV dark matter particles annihilating directly to <ref:2603.12314#pg3,to the yields predicted for 50 GeV dark matter particles annihilating directly>.

Vera: So, to summarize these improvements, the paper points toward a more systematic way of searching for the optimal parameters by mapping out the parameter space using figures S1 and S2.

Jocelyn: It also provides guidance on which decay channel is likely to give better results depending on whether you're looking at small or large scalar masses.

Subrahmanyan: And they are providing a solid benchmark by comparing their new yields against established predictions from fifty GeV dark matter annihilating directly to <ref:2603.12314#pg3>.

Conclusion: Vera: So, to wrap up this discussion on "Dark Matter, Baryon Number, and Cosmic-Ray Antinuclei". The paper suggests that these models offer a way to potentially enhance the observed cosmic-ray antinuclei fluxes.

Jocelyn: They are showing that these models can produce an order of magnitude or larger enhancement in the antideuteron and antihelium-three fluxes in the B = L = three case for small m phi <ref:2603.12314#pg1,an order of magnitude or larger enhancement in the>.

Subrahmanyan: This enhancement is driven by the larger number of antibaryons and more hadronic jets, which connects this to how we think about structure formation on a larger scale.

Vera: Ultimately, the paper suggests that these scenarios could provide a pathway to explain some of the events reported by AMS while remaining consistent with constraints from antiprotons.

Jocelyn: And they end by saying that as AMS-two continues to collect data, our understanding of antinuclei in the cosmic-ray spectrum will improve substantially over the coming years <ref:2603.12314#pg1,in the cosmic-ray spectrum>.

Subrahmanyan: The work on "Dark Matter, Baryon Number, and Cosmic-Ray Antinuclei" provides a framework for how we can look at dark matter annihilation signatures in the cosmic ray data.