| 초록 |
My research activity on Dark Matter phenomenology during the last five years was focused on two main subjects: i) the study of the impact of the first Large Hadron Collider (LHC) runs on the phenomenology of neutralino Dark Matter with a light mass of about 10 GeV (such scenario represented until 2013 the most promising particle physics explanation of several excesses observed in direct Dark Matter searches); ii) the attempt to develop a bottom-up approach to interpret the results of Dark Matter search experiments in terms of the most generic DM candidate and velocity distribution. As far as point i) is concerned, in 2011 I first showed in a paper in collaboration with the DAMA group that the annual modulation observed by their experiment during 13 years could be very well explained by light neutralinos. In a subsequent paper in 2012 I discussed in detail the expected signal from light neutralinos at the LHC, showing that at the end of the first run (with a collected luminosity of about 5 fm^{-1}) a mild excess at the level of 3 sigmas could be observed, while even after collecting 100 fm^{-1} at 14 TeV the mass reconstruction through sequential and branched squark decays would be affected by very large uncertainties. Later in the same year I reviewed the status of light neutralinos in light of the upcoming constraints from the null searches LHC and of the preliminary observation of a 125 GeV Higgs boson and combining the LHC data with constraints from B physics and the muon anomalous magnetic moment, showing that a neutralino signal could still explain DAMA but the neutralino mass lower bound was raised to almost 20 GeV. However, in a subsequent paper in 2013, after more detailed experimental data on the Higgs boson became available (in particular showing that its decay branching ratios were very similar to those predicted in the Standard Model) and lacking any signal of new physics, I showed that the ensuing constrains implied that light neutralinos could no longer reach the cross section levels to explain DAMA, although it could still be observable in an antiproton excess in PAMELA and AMS or a gamma signal in Fermi-LAT. In the same year I also solved a long-standing issue related to the calculation of the neutralino-nucleus cross section when the neutralino mass is almost degenerate to that of a squark, proving analitically that the resonant behavior predicted by public computer codes that calculate supersymmetric signals is not present. In 2012 I discussed the non-perturbative effects on the annihilation cross section of an Electro-Weak Dark Matter (EWDM) particle belonging to an electroweak multiplet when the splittings between the masses of the DM component and the other charged or neutral component(s) of the multiplet are treated as free parameters, showing for the first time that in such case EWDM exhibits not only the usual Sommerfeld enhancement with resonance peaks but also dips where the cross section is suppressed. In light of the results on light neutralinos summarized above, starting from 2014 I changed the focus of my research trying to develop a bottom-up approach complementary to the top-bottom approach adopted in the first first part with light neutralinos. In particular, I showed that compatibility between the DAMA modulation result (as well as less the CDMS Silicon effect and the excess claimed by CRESST) with constraints from other experiments can be achieved by extending the analysis of direct detection data beyond the standard elastic scattering of a WIMP off nuclei with a spin--dependent or a spin--independent cross section and with a velocity distribution as predicted by the Isothermal Sphere model. (출처 : 연구결과 요약문 4p) |
