Model-independent implications of the e+, e-, anti-proton cosmic ray spectra on properties of Dark Matter (0809.2409v5)

Abstract: Taking into account spins, we classify all two-body non-relativistic Dark Matter annihilation channels to the allowed polarization states of Standard Model particles, computing the energy spectra of the stable final-state particles relevant for indirect DM detection. We study the DM masses, annihilation channels and cross sections that can reproduce the PAMELA indications of an e+ excess consistently with the PAMELA p-bar data and the ATIC/PPB-BETS e++e- data. From the PAMELA data alone, two solutions emerge: (i) either the DM particles that annihilate into W,Z,h must be heavier than about 10 TeV or (ii) the DM must annihilate only into leptons. Thus in both cases a DM particle compatible with the PAMELA excess seems to have quite unexpected properties. The solution (ii) implies a peak in the e++e- energy spectrum, which, indeed, seems to appear in the ATIC/PPB-BETS data around 700 GeV. If upcoming data from ATIC-4 and GLAST confirm this feature, this would point to a O(1) TeV DM annihilating only into leptons. Otherwise the solution (i) would be favored. We comment on the implications of these results for DM models, direct DM detection and colliders as well as on the possibility of an astrophysical origin of the excess.

• The paper demonstrates that dark matter annihilations into leptons or gauge bosons explain cosmic ray excesses using a model-independent framework.
• The paper finds that the absence of an antiproton excess restricts viable channels, favoring either TeV-scale leptonic or >10 TeV gauge boson scenarios.
• The paper establishes how enhanced annihilation cross sections, potentially via Sommerfeld effects, are required to reconcile theoretical predictions with observed cosmic ray anomalies.

Overview of the Implications of Cosmic Ray Spectra on Dark Matter Properties

The paper "Model-independent implications of the $e^\pm, \bar{p}$ cosmic ray spectra on properties of Dark Matter," authored by M. Cirelli, M. Kadastik, M. Raidal, and A. Strumia, provides a comprehensive exploration of the implications cosmic ray data have on the characteristics of Dark Matter (DM). Utilizing observations from PAMELA, AMS, and other experiments, the paper delineates the potential impacts on the mass, annihilation channels, and cross sections of dark matter particles. The analysis seeks to explain the observed cosmic ray excesses without committing to specific dark matter models, allowing for a broad investigation into the possible properties and interactions of dark matter.

Key Findings

1. Dark Matter Annihilation Channels: The paper primarily classifies dark matter annihilation channels into two pathways: into leptons and into gauge bosons or quarks. The paper highlights that PAMELA data alone indicate two viable dark matter scenarios: either dark matter particles are heavier than about 10 TeV and annihilate into $W, Z, h$, or they predominantly annihilate into leptons.
2. Positron and Antiproton Spectra: The observed excess in positron spectra, notably above 10 GeV, suggest an intriguing anomaly that cannot be accounted for by conventional astrophysical sources. Simultaneously, the PAMELA data show no increase in the $\bar{p}/p$ ratio, limiting the potential annihilation channels that result in antiproton production.
3. Dark Matter Mass Constraints: The paper framework conclusively posits dark matter particle masses. If dark matter primarily annihilates into leptons, the mass is constrained to the TeV scale to account for the observed spectral peaks in the ATIC/PPB-BETS data. Alternatively, for annihilation into gauge bosons, heavier masses (>10 TeV) are favored.
4. Boost Factors and Annihilation Cross Sections: With the observed cosmic ray anomalies requiring enhanced annihilation cross sections, potential explanations include non-thermal dark matter production or mechanisms like the Sommerfeld enhancement, where the cross-section increases at low velocities.
5. Model Independent Analysis: A strength of the paper lies in its model-independent approach, constructing energy spectra for different annihilation channels without subscribing to a specific dark matter particle theory. This allows for a versatile evaluation as new data emerge or theoretical models evolve.

Implications of the Research

Theoretical Impacts: The implications of this research are considerable for theoretical physics. By utilizing a model-independent framework, it encourages a reevaluation of existing models and broadens the landscape of theoretical dark matter candidates. It challenges the traditional WIMP paradigm and suggests that dark matter particles might have properties significantly different from those commonly considered.

Practical Impacts: Practically, this research indicates specific areas of focus for future experimental efforts. Experiments like GLAST or forthcoming extensions of AMS can confirm or refine the present indications, improving the constraints on dark matter properties. Specifically, high-energy cosmic ray studies serve as crucial tests for determining the viability of the proposed dark matter interactions.

Future Directions: The results prompt further research into both particle physics and astrophysical phenomena, particularly exploring alternative sources or explanations for the observed cosmic ray signals, such as pulsars or other exotic astrophysical objects. Future studies could refine propagation models and investigate potential correlations with other observational windows, such as gamma-rays or neutrinos.

In conclusion, the examined cosmic ray spectra provide a critical avenue for understanding dark matter properties, suggesting intriguing anomalies that challenge conventional theories. This work is essential for directing the future path of both experimental programs and theoretical developments to decode the enigmatic nature of dark matter in our universe.