Electroweak fragmentation functions for dark matter annihilation

Electroweak corrections can play a crucial role in dark matter annihilation. The emission of gauge bosons, in particular, leads to a secondary flux consisting of all Standard Model particles, and may be described by electroweak fragmentation functions. To assess the quality of the fragmentation function approximation to electroweak radiation in dark matter annihilation, we have calculated the flux of secondary particles from gauge-boson emission in models with Majorana fermion and vector dark matter, respectively. For both models, we have compared cross sections and energy spectra of positrons and antiprotons after propagation through the galactic halo in the fragmentation function approximation and in the full calculation. Fragmentation functions fail to describe the particle fluxes in the case of Majorana fermion annihilation into light fermions: the helicity suppression of the lowest-order cross section in such models cannot be lifted by the leading logarithmic contributions included in the fragmentation function approach. However, for other classes of models like vector dark matter, where the lowest-order cross section is not suppressed, electroweak fragmentation functions provide a simple, model-independent and accurate description of secondary particle fluxes.Comment: 18 pages, matches the published versio

Constraints on leptophilic dark matter from the AMS-02 experiment

The annihilation of dark matter particles in the galactic halo of the Milky Way may lead to cosmic ray signatures that can be probed by the AMS-02 experiment, which has measured the composition and fluxes of charged cosmic rays with unprecedented precision. Given the absence of characteristic spectral features in the electron and positron fluxes measured by AMS-02, we derive upper limits on the dark matter annihilation cross section for leptophilic dark matter models. Our limits are based on a new background model that describes all recent measurements of the energy spectra of cosmic ray positrons and electrons. For thermal dark matter relics, we can exclude dark matter masses below about 100 GeV. We include the radiation of electroweak gauge bosons in the dark matter annihilation process and compute the antiproton signal that can be expected within leptophilic dark matter models.Comment: 7 pages, 3 figures, 1 table. Matches the published version apart from typo corrected in Eq.

Observation of Fine Time Structures in the Cosmic Proton and Helium Fluxes with the Alpha Magnetic Spectrometer on the International Space Station

International audienceWe present the precision measurement from May 2011 to May 2017 (79 Bartels rotations) of the proton fluxes at rigidities from 1 to 60 GV and the helium fluxes from 1.9 to 60 GV based on a total of $1 \times 10^9$ events collected with the Alpha Magnetic Spectrometer aboard the International Space Station. This measurement is in solar cycle 24, which has the solar maximum in April 2014. We observed that, below 40 GV, the proton flux and the helium flux show nearly identical fine structures in both time and relative amplitude. The amplitudes of the flux structures decrease with increasing rigidity and vanish above 40 GV. The amplitudes of the structures are reduced during the time period, which started one year after solar maximum, when the proton and helium fluxes steadily increase. Above $\sim 3$  GV the p/He flux ratio is time independent. We observed that below $\sim 3$  GV the ratio has a long-term decrease coinciding with the period during which the fluxes start to rise

Searches for leptophilic dark matter with astrophysical experiments

One of the most exciting goals of particle and astroparticle physics is the understanding of the nature of dark matter (DM). A huge experimental effort is made to detect DM, under the assumption that some interaction with Standard Model particles exists, besides gravitation. In particular, DM in our Galaxy might annihilate into standard model particles and provide an additional contribution to cosmic ray fluxes. Precise measurements of the cosmic rays fluxes are therefore crucial. The AMS-02 experiment measures the fluxes of charged cosmic rays with unprecedented precision. From the theory side, viable dark matter candidates are provided both as byproducts of well motivated extensions of the standard model and by minimal models. Cosmic rays measurements can be used to probe these DM models. For this, two ingredients are necessary. First, appropriate predictions for the fluxes due to dark matter annihilation in the Galaxy are needed. Second, to be able to detect this exotic cosmic rays contributions, a reliable description of the fluxes of astrophysical origin is required. In this work, we focus on a specific class of DM models, the so-called leptophilic models, where DM annihilates at tree-level only into electron-positron pairs. We first discuss the importance of the inclusion of electroweak (EW) radiation for the theoretical predictions for the DM-induced cosmic ray fluxes. In particular, we study the range of applicability and limitations of a model-independent formalism to include the emission of EW gauge bosons. The inclusion of EW radiation is particularly relevant for leptophilic models, as it induces fluxes of hadrons, neutrinos and photons, that would otherwise be neglected. We then introduce a phenomenological model for the electron and positron fluxes of astrophysical origin. Under the assumption that the energy spectra of astrophysical fluxes are smooth, this model describes them with twelve parameters. We determine these parameters by fitting the model to the AMS-02 measurements of electron and positron fluxes. Dark matter annihilation in the Galaxy would induce additional spectral features on top of the smooth background. Given the absence of statistically significant spectral features in the AMS-02 measurements, we derive new upper limits on the DM annihilation cross section for leptophilic models in general. Assuming that the DM annihilation cross section is close to this upper limit, we obtain predictions for the expected antiproton flux due to the decay of EW gauge bosons. These fluxes can be compared to available measurements. Finally, we briefly study leptophilic DM at the Large Hadron Collider. We consider a specific model and compute the DM production cross section, that is loop-induced in the scenario under study

Electroweak fragmentation functions for dark matter annihilation

Electroweak corrections are relevant for dark matter indirect detection predictions. The quality of the fragmentation function approximation to describe electroweak gauge boson radiation is examined in two concrete models. For models with Majorana fermion dark matter annihilation into light fermions, the fragmentation function approximation does not work, due to the helicity suppression of the lowest-order cross section. For other models, like those with vector dark matter, fragmentation functions provide very reliable results for dark matter with masses $M_{\rm DM} \gtrsim 500$\,GeV

Exploring Dark Matter with AMS-02 through Electroweak Corrections

The AMS-02 experiment is now measuring charged cosmic rays fluxes with an unprecedented precision. It is thus necessary to provide appropriate and complementary predictions for dark matter signals. To that end, computing electroweak corrections to the dark matter annihilation is an important task. It is particularly relevant for leptophilic models where anti-protons can be produced through the decay of massive gauge bosons. From the lack of particular spectral features in the AMS positron flux, we derive new model independent upper limits on the annihilation cross section. In particular we use a newly introduced background function that allows to set limits using all the energy spectrum probed by AMS-02. This is particularly interesting as important phenomena such as solar modulation take place at low energy. Using a new calculation of electroweak radiation for vector dark matter annihilation, we can predict the maximum flux of anti-protons in such leptophilic scenarios, to be compared with future AMS measurments

Properties of Cosmic Helium Isotopes Measured by the Alpha Magnetic Spectrometer

International audiencePrecision measurements by the Alpha Magnetic Spectrometer (AMS) on the International Space Station of $^{3}He$ and $^{4}He$ fluxes are presented. The measurements are based on 100 million $^{4}He$ nuclei in the rigidity range from 2.1 to 21 GV and 18 million He3 from 1.9 to 15 GV collected from May 2011 to November 2017. We observed that the $^{3}He$ and $^{4}He$ fluxes exhibit nearly identical variations with time. The relative magnitude of the variations decreases with increasing rigidity. The rigidity dependence of the $^{3}He/^{4}He$ flux ratio is measured for the first time. Below 4 GV, the $^{3}He/^{4}He$ flux ratio was found to have a significant long-term time dependence. Above 4 GV, the $^{3}He/^{4}He$ flux ratio was found to be time independent, and its rigidity dependence is well described by a single power law $\alpha R^{\Delta}$ with $\Delta=-0.294±0.004$. Unexpectedly, this value is in agreement with the B/O and B/C spectral indices at high energies

Properties of Iron Primary Cosmic Rays: Results from the Alpha Magnetic Spectrometer

International audienceWe report the observation of new properties of primary iron (Fe) cosmic rays in the rigidity range 2.65 GV to 3.0 TV with 0.62×10$^6$ iron nuclei collected by the Alpha Magnetic Spectrometer experiment on the International Space Station. Above 80.5 GV the rigidity dependence of the cosmic ray Fe flux is identical to the rigidity dependence of the primary cosmic ray He, C, and O fluxes, with the Fe/O flux ratio being constant at 0.155±0.006. This shows that unexpectedly Fe and He, C, and O belong to the same class of primary cosmic rays which is different from the primary cosmic rays Ne, Mg, and Si class