New Positron Spectral Features from Supersymmetric Dark Matter - a Way to Explain the PAMELA Data?

Abstract: The space-borne antimatter experiment PAMELA has recently reported a surprising rise in the positron to electron ratio at high energies. It has also recently been found that electromagnetic radiative corrections in some cases may boost the gamma-ray yield from supersymmetric dark matter annihilations in the galactic halo by up to three or four orders of magnitude, providing distinct spectral signatures for indirect dark matter searches to look for. Here, we investigate whether the same type of corrections can also lead to sizeable enhancements in the positron yield. We find that this is indeed the case, albeit for a smaller region of parameter space than for gamma rays; selecting models with a small mass difference between the neutralino and sleptons, like in the stau coannihilation region in mSUGRA, the effect becomes more pronounced. The resulting, rather hard positron spectrum with a relatively sharp cutoff may potentially fit the rising positron ratio measured by the PAMELA satellite. To do so, however, very large "boost factors" have to be invoked that are not expected in current models of halo structure. If the predicted cutoff would also be confirmed by later PAMELA data or upcoming experiments, one could either assume non-thermal production in the early universe or non-standard halo formation to explain such a spectral feature as an effect of dark matter annihilation. At the end of the paper, we briefly comment on the impact of radiative corrections on other annihilation channels, in particular antiprotons and neutrinos.

• The paper demonstrates that electromagnetic radiative corrections during neutralino annihilations can enhance the positron yield to explain PAMELA observations.
• It details a theoretical analysis using mSUGRA and MSSM-9 scans, focusing on the stau coannihilation region to identify conditions for a hard positron spectrum.
• The study highlights that the required boost factors imply non-standard astrophysical processes, urging further experimental verification of the model.

Theoretical Exploration of Positron Spectra from Supersymmetric Dark Matter in Relation to PAMELA Data

This paper provides a detailed theoretical investigation into the potential explanation of anomalies observed in the positron to electron ratio data reported by the PAMELA satellite experiment. The authors focus on the context of supersymmetric dark matter, specifically analyzing how electromagnetic radiative corrections during annihilation processes in the galactic halo could impact the positron yield, offering distinct spectral signatures for indirect dark matter detection.

Key Findings

The paper discusses the phenomenon in which electromagnetic radiative corrections can significantly increase the gamma-ray yield from neutralino annihilations, potentially explaining the positron flux observed by PAMELA under certain conditions. The authors investigate if similar effects could enhance the positron yield. They find that the enhancement is possible, particularly in scenarios where the mass difference between the neutralino and sleptons is minimal, such as in the stau coannihilation region of mSUGRA models. This parameter space feature results in a relatively hard positron spectrum that aligns with PAMELA's unexpected positron ratio increase. However, the enhancement requires substantial "boost factors," which are atypical in current halo structure models.

Analytical Methodology

The paper deploys a thorough theoretical framework to compute the yield of positrons from supersymmetric dark matter annihilation, integrating considerations of radiative corrections. The focus is on the coannihilation region where the mass of the lightest selectron closely matches the mass of the neutralino, enhancing positron production due to the breakdown of helicity suppression. By conducting parameter scans over both the mSUGRA and MSSM-9 models, the authors map the conditions under which substantial positron flux enhancements are observed.

Implications of Numerical Results

The numerical results underscore a significant challenge in aligning theoretical predictions with experimental data, primarily due to the need for large boost factors to achieve the observed positron flux levels. This requirement suggests that either non-standard particle production mechanisms are at play, or there are unknown astrophysical processes influencing halo formation and structure. The authors also highlight the predictive capability of their model regarding the positron spectrum's cutoff, which should, theoretically, occur just beyond the current observational limits if the dark matter interpretation holds.

Theoretical and Practical Implications

The exploration of radiative corrections and their impact on positron yields adds depth to the theoretical understanding of indirect detection methods in dark matter research, particularly supersymmetric frameworks. Practically, if the posited radiative enhancements are accurate, subsequent experimental verification through cosmic ray measurements would necessitate reconsideration of existing constraints and models in dark matter analyses.

Speculation on Future Developments

Future explorations might entail refining the constraints on parameter spaces enabling high-yield positron signatures while maintaining consistency with relic density and collision experiments' findings. Moreover, upcoming experiments like AMS-02 and improvements in gamma-ray telescopic capabilities could directly test the predictions regarding spectral cutoffs, potentially corroborating or refuting these theoretical insights.

Overall, the paper presents a rigorous investigation with significant potential implications for the field of dark matter research, particularly within the framework of supersymmetric theories. The intricate linkage of theoretical predictions with observable phenomena like PAMELA's results exemplifies the complex interplay between astrophysical research and particle physics.