Search

We reinterpret the results of the direct searches for dark matter in terms of composite dark matter, i.e. dark matter particles that form neutral bound states, generically called dark atoms, either with ordinary particles, or with other dark matter particles. Three different scenarios are investigated: the O-helium scenario, milli- interacting dark matter and dark anti-atoms. In each of them, dark matter interacts sufficiently strongly with terrestrial matter to be stopped in it before reaching underground detectors. As they drift towards the center of the earth by gravity, these thermal dark atoms are radiatively captured by the atoms of the active medium of underground detectors, which causes the emission of photons that produce the signals through their interactions with the electrons of the medium. This provides a way of reinterpreting the results in terms of electron recoils instead of nuclear recoils. The detailed study of the interactions of O-helium with ordinary matter shows that it is not an acceptable candidate for dark matter because of the absence of a repulsion mechanism preventing it from falling into the deep nuclear wells of nuclei. The two other models involve milli-charges and are able to reconcile the most contradictory experiments. We determine, for each model, the regions in the parameter space that reproduce the experiments with positive results in full consistency with the constraints of the experiments with negative results. We also pay attention to the experimental and observational constraints on milli-charges and discuss some typical signatures of the models that could be used to test them., Comment: PhD thesis, defended on September 9, 2015 at the University of Li\`ege, Belgium

Among composite-dark-matter scenarios, one of the simplest and most predictive is that of O-helium (OHe) dark atoms, in which a lepton-like doubly charged particle O is bound with a primordial helium nucleus, and is the main constituent of dark matter. This model liberates the physics of dark matter from many unknown features of new physics, and it demands a deep understanding of the details of known nuclear and atomic physics, which are still somewhat unclear in the case of nuclear interacting "atomic" shells. So far the model has relied on the dominance of elastic scattering of OHe with the matter. In view of the uncertainty in our understanding of OHe interaction with nuclei we study the opposite scenario, in which inelastic nuclear reactions dominate the OHe interactions with nuclei. We show that in this case all the OHe atoms bind with extra He nuclei, forming doubly charged O-beryllium ions, which behave like anomalous helium, causing potential problems with overabundance of anomalous isotopes in terrestrial matter., Comment: To appear in Proceedings of the 17th Bled Workshop "What Comes Beyond Standard Models?"

We show that the existence of a sub-dominant form of dark matter, made of dark antiatoms of mass and size of the order of 1 TeV and 30 fm respectively, can explain the results of direct detection experiments, with a positive signal in DAMA/NaI and DAMA/LIBRA and no signal in other experiments. The signal comes from the binding of the dark antiatoms to thallium, a dopant in DAMA, and is not present for the constituent atoms of other experiments. The dark antiatoms are made of two particles oppositely charged under a dark U(1) symmetry and can bind to terrestrial atoms because of a kinetic mixing between the photon and the massless dark photon, such that the dark particles acquire an electric millicharge of the order of 0.0005e. This millicharge enables them to bind to high-Z atoms via radiative capture, after they thermalize in terrestrial matter through elastic collisions., Comment: 18 pages, 5 figures

New stable quarks and charged leptons may exist and be hidden from detection, as they are bound by Coulomb interaction in neutral dark atoms of composite dark matter. This possibility leads to fundamentally new types of indirect effects related to the excitation of such dark atoms followed by their electromagnetic de-excitation. Stable -2 charged particles, bound to primordial helium in O-helium (OHe) atoms, represent the simplest model of dark atoms. Here we consider the structure of OHe atomic levels which is a necessary input for the indirect tests of such composite dark matter scenarios, and we give the spectrum of electromagnetic transitions from the levels excited in OHe collisions., Comment: Invited contribution to the special issue of Modern Physics Letters A "Indirect dark matter searches"

It was recently proposed that stable particles of charge $-2$, $O^{--}$, can exist and constitute dark matter after they bind with primordial helium in O-helium (OHe) atoms. We study here in details the possibility that this model provides an explanation for the excess of gamma radiation in the positron-annihilation line from the galactic bulge observed by INTEGRAL. This explanation assumes that OHe, excited to a 2s state through collisions in the central part of the Galaxy, de-excites to its ground state via an E0 transition, emitting an electron-positron pair. The cross section for OHe collisions with excitation to 2s level is calculated and it is shown that the rate of such excitations in the galactic bulge strongly depends not only on the mass of O-helium, which is determined by the mass of $O^{--}$, but also on the density and velocity distribution of dark matter. Given the astrophysical uncertainties on these distributions, this mechanism constrains the $O^{--}$ mass to lie in two possible regions. One of these is reachable in the experimental searches for stable multicharged particles at the LHC., Comment: 8 pages, 1 figure

We reinterpret the results of the direct searches for dark matter in terms of milli-interacting dark particles. The model reproduces the positive results from DAMA/LIBRA and CoGeNT and is consistent with the absence of signal in the XENON100, CDMS-II/Ge and LUX detectors. Dark atoms, interacting with standard atoms through a kinetic mixing between photons and dark photons and a mass mixing of {\sigma} mesons with dark scalars, diffuse elastically in terrestrial matter where they deposit all their energy. Reaching underground detectors through gravity at thermal energies, they form bound states with nuclei of the active medium by radiative capture, which causes the emission of photons that produce the observed signals. The parameter space of the model is explored and regions reproducing the results at the 2{\sigma} level are obtained for each experiment., Comment: 12 pages, 1 figure

Up-to-date estimates of the cosmological parameters are presented as a result of numerical simulations of cosmic microwave background and large scale structure, considering a flat Universe in which the dark matter is made entirely or partly of mirror matter, and the primordial perturbations are scalar adiabatic and in linear regime. A statistical analysis using the Markov Chain Monte Carlo method allows to obtain constraints of the cosmological parameters. As a result, we show that a Universe with pure mirror dark matter is statistically equivalent to the case of an admixture with cold dark matter. The upper limits for the ratio of the temperatures of ordinary and mirror sectors are around 0.3 for both the cosmological models, that show the presence of a dominant fraction of mirror matter, $0.06 \lesssim \Omega_{\rm mirror} h^2 \lesssim 0.12$., Comment: 6 pages, 3 figures

We present a dark matter model reproducing well the results from DAMA/LIBRA and CoGeNT and having no contradiction with the negative results from XENON100 and CDMS-II/Ge. Two new species of fermions F and G form hydrogen-like atoms with standard atomic size through a dark U(1) gauge interaction carried out by a dark massless photon. A Yukawa coupling between the nuclei F and neutral scalar particles S induces an attractive shorter-range interaction. This dark sector interacts with our standard particles because of the presence of two mixings, a kinetic photon-dark photon mixing, and a mass {\sigma}-S mixing. The dark atoms from the halo diffuse elastically in terrestrial matter until they thermalize and then reach underground detectors with thermal energies, where they form bound states with nuclei by radiative capture. This causes the emission of photons that produce the signals observed by direct-search experiments., Comment: 14 pages, 3 figures

A recent composite-dark-matter scenario assumes that the dominant fraction of dark matter consists of O-helium (OHe) dark atoms, in which a lepton-like doubly charged particle O is bound with a primordial helium nucleus. It liberates the physics of dark matter from unknown features of new physics, but it demands a deep understanding of the details of known nuclear and atomic physics, which are still unclear. Here, we consider in detail the physics of the binding of OHe to various nuclei of interest for direct dark matter searches. We show that standard quantum mechanics leads to bound states in the keV region, but does not seem to provide a simple mechanism that stabilizes them. The crucial role of a barrier in the OHe-nucleus potential is confirmed for such a stabilization., Comment: Contribution to the proceedings of the 15th Workshop "What Comes Beyond the Standard Models", Bled, July 9-19, 2012

We present new fast numerical simulations of cosmic microwave background and large scale structure in the case in which the cosmological dark matter is made entirely or partly of mirror matter. We consider scalar adiabatic primordial perturbations at linear scales in a flat Universe. The speed of the simulations allows us for the first time to use Markov Chain Monte Carlo analyses to constrain the mirror parameters. A Universe with pure mirror matter can fit very well the observations, equivalently to the case of an admixture with cold dark matter. In both cases, the analyses show a clear indication of the presence of a consistent amount of mirror dark matter, $0.06 \lesssim \Omega_{\rm mirror} h^2 \lesssim 0.12$., Comment: 5 pages, 2 figures; reuses introductory material from arXiv:1102.5530; results updated, matches the published version