1,302 research outputs found
Constraints on dark matter annihilation from AMS-02 results
We use recently released data on the positron-to-electron ratio in cosmic
rays from the AMS-02 experiment to constrain dark matter annihilation in the
Milky Way. Due to the yet unexplained positron excess, limits are generally
weaker than those obtained using other probes, especially gamma rays. This also
means that explaining the positron excess in terms of dark matter annihilation
is difficult. Only if very conservative assumptions on the dark matter
distribution in the Galactic Center region are adopted, it may be possible to
accommodate dark matter annihilating to leptons with a cross section above
10^-24 cm^3/sec. We comment on several theoretical mechanisms to explain such
large annihilation cross sections.Comment: 6 pages, 2 figures, v2: improved treatment of astrophysical
uncertainties, improved discussion, matches published versio
Flavor and CP violation in Higgs decays
Flavor violating interactions of the Higgs boson are a generic feature of
models with extended electroweak symmetry breaking sectors. Here, we
investigate CP violation in these interactions, which can arise from
interference of tree-level and 1-loop diagrams. We compute the CP asymmetry in
flavor violating Higgs decays in an effective field theory with only one Higgs
boson and in a general Type-III Two Higgs Doublet Model (2HDM). We find that
large (~ O(10%)) asymmetries are possible in the 2HDM if one of the extra Higgs
bosons has a mass similar to the Standard Model Higgs. For the poorly
constrained decay modes h -> tau mu and h -> tau e, this implies that large
lepton charge asymmetries could be detectable at the LHC. We quantify this by
comparing the sensitivity of the LHC to existing direct and indirect
constraints. Interestingly, detection prospects are best if Higgs mixing is
relatively small - a situation that is preferred by the current data.
Nevertheless, CP violation in h -> tau mu or h -> tau e will only be observable
if nonzero rates for these decay modes are measured very soon.Comment: 17 pages, 5 figure
A m\'enage \`a trois of eV-scale sterile neutrinos, cosmology, and structure formation
We show that sterile neutrinos with masses ~1 eV or larger, as motivated by
several short-baseline oscillation anomalies, can be consistent with
cosmological constraints if they are charged under a hidden sector force
mediated by a light boson. In this case, sterile neutrinos experience a large
thermal potential that suppresses mixing between active and sterile neutrinos
in the early Universe, even if vacuum mixing angles are large. Thus, the
abundance of sterile neutrinos in the Universe remains very small, and their
impact on Big Bang Nucleosynthesis, Cosmic Microwave Background, and
large-scale structure formation is negligible. It is conceivable that the new
gauge force also couples to dark matter, possibly ameliorating some of the
small-scale structure problems associated with cold dark matter.Comment: 7 pages, 4 figures. v3: minor corrections in the discussion of small
scale structure led to the realization that all 3 problems can be solved
simultaneously. Matches PRL version titled "Cosmologically Safe eV-Scale
Sterile Neutrinos and Improved Dark Matter Structure". v4: references added,
calculations in appendix A rewritten in Feynman gauge. ArXiv version includes
2 additional figure
The Not-So-Sterile 4th Neutrino: Constraints on New Gauge Interactions from Neutrino Oscillation Experiments
Sterile neutrino models with new gauge interactions in the sterile sector are
phenomenologically interesting since they can lead to novel effects in neutrino
oscillation experiments, in cosmology and in dark matter detectors, possibly
even explaining some of the observed anomalies in these experiments. Here, we
use data from neutrino oscillation experiments, in particular from MiniBooNE,
MINOS and solar neutrino experiments, to constrain such models. We focus in
particular on the case where the sterile sector gauge boson couples also
to Standard Model particles (for instance to the baryon number current) and
thus induces a large Mikheyev-Smirnov-Wolfenstein potential. For eV-scale
sterile neutrinos, we obtain strong constraints especially from MINOS, which
restricts the strength of the new interaction to be less than times
that of the Standard Model weak interaction unless active-sterile neutrino
mixing is very small (). This rules out
gauge forces large enough to affect short baseline experiments like MiniBooNE
and it imposes nontrivial constraints on signals from sterile neutrino
scattering in dark matter experiments.Comment: 19 pages, 9 figure
Testing the wave packet approach to neutrino oscillations in future experiments
When neutrinos propagate over long distances, the mass eigenstate components
of a flavor eigenstate will become spatially separated due to their different
group velocities. This can happen over terrestrial distance scales if the
neutrino energy is of order MeV and if the neutrino is localized (in a quantum
mechanical sense) to subatomic scales. For example, if the Heisenberg
uncertainty in the neutrino position is below 0.01 Angstrom, neutrino
decoherence can be observed in reactor neutrinos using a large liquid
scintillator detector.Comment: LaTeX, 7 pages, 3 figures; in v1, we had concluded that wave packet
decoherence may be observable in experiments like Hanohano or LENA. As
pointed out to us by E. Akhmedov, G. Raffelt, and L. Stodolsky, this
conclusion is INCORRECT since it was based on incorrect estimates for the
size of the neutrino wave packets. The paper will be revised to explain this
problem and to address related question
Global interpretation of direct Dark Matter searches after CDMS-II results
We perform a global fit to data from Dark Matter (DM) direct detection
experiments, including the recent CDMS-II results. We discuss possible
interpretations of the DAMA annual modulation signal in terms of
spin-independent and spin-dependent DM-nucleus interactions, both for elastic
and inelastic scattering. We find that in the spin-dependent inelastic
scattering off protons a good fit to all data is obtained. We present a simple
toy model realizing such a scenario. In all the remaining cases the DAMA
allowed regions are disfavored by other experiments or suffer from severe fine
tuning of DM parameters with respect to the galactic escape velocity. Finally,
we also entertain the possibility that the two events observed in CDMS-II are
an actual signal of elastic DM scattering, and we compare the resulting CDMS-II
allowed regions to the exclusion limits from other experiments.
In this arXiv version of the manuscript we also provide in appendix A the
updated fits including recent CoGeNT results.Comment: 23 pages, 9 figures, added appendix on interpretation of recent
CoGeNT result, the rest of the manuscript mirrors published versio
Neutrino factory optimization for non-standard interactions
We study the optimization of a neutrino factory with respect to non-standard
neutral current neutrino interactions, and compare the results to those
obtained without non-standard interactions. We discuss the muon energy,
baselines, and oscillation channels as degrees of freedom. Our conclusions are
based on both analytical calculations and on a full numerical simulation of the
neutrino factory setup proposed by the international design study (IDS-NF). We
consider all possible non-standard parameters, and include their complex
phases. We identify the impact of the different parameters on the golden,
silver, and disappearance channels. We come to the conclusion that, even in the
presence of non-standard interactions, the performance of the neutrino factory
hardly profits from a silver channel detector, unless the muon energy is
significantly increased compared to the IDS-NF setup. Apart from the
dispensable silver channel detector, we demonstrate that the IDS-NF setup is
close to optimal even if non-standard interactions are considered. We find that
one very long baseline is a key component in the search for non-standard
interactions, in particular for |\epsilon^m_{\mu\tau}| and
|\epsilon^m_{\tau\tau}|.Comment: LaTeX, 30 pages, 7 figures, 1 tabl
Loopy Constraints on Leptophilic Dark Matter and Internal Bremsstrahlung
A sharp and spatially extended peak in an astrophysical gamma ray spectrum
would provide very strong evidence for the existence of dark matter (DM), given
that there are no known astrophysical processes that could mimic such a signal.
From the particle physics perspective, perhaps the simplest explanation for a
gamma ray peak is internal bremsstrahlung in DM annihilation through a charged
t-channel mediator eta close in mass to the DM particle chi. Since DM
annihilation to quarks is already tightly constrained in this scenario, we
focus here on the leptophilic case. We compute the electromagnetic anapole and
dipole moments that DM acquires at 1-loop, and we find an interesting
enhancement of these moments if the DM particle and the mediator are close in
mass. We constrain the DM anapole and dipole moments using direct detection
data, and then translate these limits into bounds on the DM annihilation cross
section. Our bounds are highly competitive with those from astrophysical gamma
ray searches. In the second part of the paper, we derive complementary
constraints on internal bremsstrahlung in DM annihilation using LEP mono-photon
data, measurements of the anomalous magnetic moments of the electron and the
muon, and searches for lepton flavor violation. We also comment on the impact
of the internal bremsstrahlung scenario on the hyperfine splitting of true
muonium.Comment: 16 pages, 16 figures, Journal accepted version, read it
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