arXiv subjects
Publications and source records attributed to S. V. Demidov.
We consider collider signatures of the hylogenesis --- a variant of antibaryonic dark matter model. We obtain bounds on the model parameters from results of the first LHC run. Also we suggest several new channels relevant for probing the antibaryonic dark matter at LHC.
We analyse sensitivity of the gigaton volume telescope Baikal-GVD for detection of neutrino signal from dark matter annihilations or decays in the Galactic Center. Expected bounds on dark matter annihilation cross section and its lifetime are found for several annihilation/decay channels.
We point out that recently discovered 3.5 keV line in X-ray spectra from various galaxy clusters and the Andromeda galaxy can be naturally explained by physics of a sector responsible for spontaneous supersymmetry breaking in models with R-parity. In this scenario the source of this line could be decay of sgoldstino - scalar superpartner of massive gravitino. At the same time the dominant dark matter component is stable gravitino whose mass is predicted to be about 0.25 GeV.
We have analyzed a data set taken over 2.76 years live time with the Baikal neutrino telescope NT200. The goal of the analysis is to search for neutrinos from dark matter annihilation in the center of the Sun. Apart from the conventional annihilation channels $b\bar{b}$, $W^+W^-$ and $τ^+τ^-$ we consider also the annihilation of dark matter particles into monochromatic neutrinos. From the absence of any excess of events from the direction of the Sun over the expected background, we derive 90% upper limits on the fluxes of muons and muon neutrinos from the Sun, as well as on the elastic cross sections of dark matter scattering on protons.
We present a new dataset analysis of the neutrino experiment at the Baksan Underground Scintillator Telescope with muon energy threshold about 1 GeV for the longest exposure time toward the Sun. In search for a signal from self-annihilations of dark matter particles in the center of the Sun we use an updated sample of upward through-going muons for 24.12 years of live time. No observable excess has been found in measured muons relative to expected background from neutrinos of atmospheric origin. We present an improved data analysis procedure and describe it in detail. We set the 90\% C.L. new upper limits on expected neutrino and muon fluxes from dark matter annihilations in the Sun, on the corresponding annihilation rates and cross sections of their elastic scattering off proton.
We present a calculation of the branching ratio of orthopositronium decay into an invisible mode, which is done in the context of Mirror World models, where ordinary positronium can disappear from our world due to oscillation into its mirror twin. In this revision we clarify some formulas and approximations used previously, correct them at some places, add new effects relevant for a feasible experiment and finally perform a combined analysis. We include into consideration various effects due to external magnetic and electric fields, collisions with cavity walls and scattering off gas atoms in the cavity. Oscillations of the Rydberg positroniums are also considered. To perform a numerical estimates in a realistic case we wrote computer code, which can be adopted in any experimental setup. Its work is illustrated with an example of a planned positronium experiment within the AEgIS project.
In supersymmetric extensions of the Standard Model of particle physics (SM), goldstino superpartners --- scalar and pseudoscalar sgoldstinos --- can be light enough for emerging in decays of SM particles. Sgoldstino interaction with SM fields is suppressed by the scale of supersymmetry breaking in the whole theory. Hence, searches for sgoldstinos give an opportunity to probe the underlying mechanism of supersymmetry breaking. Sgoldstino couplings to SM fields are proportional to the supersymmetry breaking parameters --- MSSM soft terms --- and therefore can lead to flavor violating processes in quark and lepton sectors. We consider flavor violating processes involving sgoldstino pair production which are driven by sgoldstino couplings proportional to squark and slepton soft mass terms, \tilde{m^2_{LL}} and \tilde{m^2_{RR}}. We find that present limits on off-diagonal entries in squark and slepton squared mass matrices allow t-, b-, c-quark and τ-lepton decays at levels available for study with existing data (BaBar, Belle, CLEOc) and in ongoing experiments (LHCb, CMS, ATLAS). In particular, we obtain the following branching ratios Br(t--> c SP)\lesssim 10^{-7}, Br(τ--> μSP) \lesssim 10^{-7}, Br(B_s--> SP) \lesssim 10^{-4}, Br(B--> K^{(*)} SP) \lesssim 10^{-4}, Br(D--> SP) \lesssim 10^{-7} with sgoldstino subsequent decays into kinematically allowed pairs of SM particles γγ, e^+e^-, μ^+μ^-, etc. Remarkably, the prominent signature of sgoldstino pair production is two muon pairs with pair momenta peaked at sgoldstino masses.
We study classical production of soliton-antisoliton pairs from colliding wave packets in (1+1)-dimensional scalar field model. Wave packets represent multiparticle states in quantum theory; we characterize them by energy E and particle number N. Sampling stochastically over the forms of wave packets, we find the entire region in (E,N) plane which corresponds to classical creation of soliton pairs. Particle number is parametrically large within this region meaning that the probability of soliton-antisoliton pair production in few-particle collisions is exponentially suppressed.
We propose general semiclassical method for computing the probability of soliton-antisoliton pair production in particle collisions. The method is illustrated by explicit numerical calculations in (1+1)-dimensional scalar field model. We find that the probability of the process is suppressed by an exponentially small factor which is almost constant at high energies.
New physics coupled to the Higgs boson may hide it in the standard decay channels to be investigated at LHC. We consider the models where new invisible dominant decay modes of the Higgs boson are responsible for this hiding. We propose to study at LHC the weak boson production associated with heavy quarks: our analysis revealed that boson pair invariant mass distribution is sensitive to both mass and width of the invisible Higgs boson, if it is not too far from the weak boson pair threshold. We present tree-level results for the most relevant cases of top quarks and of bottom quarks in Standard Model extensions with large $b$-quark Yukawa coupling. We argue that QCD corrections do not spoil these results allowing for unambiguous extraction of the Higgs boson mass and width from the analysis of large enough amount of data.
With use of CompHEP package we've made the detailed estimate of the influence of double e+e- pair production by photons (DPP) on the propagation of ultra high energy electromagnetic cascade. We show that in the models in which cosmic ray photons energy reaches few thousand EeV refined DPP analysis may lead to substantial difference in predicted photon spectrum compared to previous rough estimates.
We present an extension of the minimal split supersymmetry model, which is capable of explaining the baryon asymmetry of the Universe. Instead of MSSM we start from NMSSM and split its spectrum in such a way that the low energy theory contains neutral particles, in addition to the content of minimal split supersymmetry. They trigger the strongly first order electroweak phase transition (EWPT) and provide an additional source of CP-violation. In this model, we estimate the amount of the baryon asymmetry produced during EWPT, using WKB approximation for CP-violating sources in diffusion equations. We also examine the contribution of CP-violating interactions to the electron and neutron electric dipole moments and estimate the production of the neutralino dark matter. We find that both phenomenological and cosmological requirements can be fulfilled in this model.
We further discuss possible sgoldstino interpretation of the observation, reported by the HyperCP collaboration, of three Σ^+\to pμ^+μ^- decay events with dimuon invariant mass 214.3 MeV within detector resolution. With sgoldstino mass equal to 214.3 MeV, this interpretation can be verified at existing and future B- and ϕ-factories. We find that the most natural values of the branching ratios of two-body B- and D-meson decays to sgoldstino P and vector meson V are about 10^{-6}\div10^{-7}. The branching ratios of ϕ-meson decay ϕ\to Pγis estimated to be in the range 1.8\cdot 10^{-13} ÷1.6\cdot 10^{-7}, depending on the hierarchy of supersymmetry breaking soft terms. Similar branchings for ρ- and ω-mesons are in the range 10^{-14}÷3.4\cdot 10^{-7}.
At hadron colliders the $γγ+jet$ channel provides larger signal-to-background ratio in comparison with inclusive $γγ$ channel in hunting for scalars uncharged under the SM gauge group. At NLO in QCD perturbation theory we evaluate selfconsistently the signal significance for the SM Higgs boson production in $γγ+jet$ channel at LHC. Three-body final state kinematics allows for refined cuts. The adjustment of these cuts increases the signal significance upto the level of inclusive channel. Applying a justified simple rescaling procedure to the results obtained for SM Higgs boson, we estimate the LHC prospects in searches for radion and sgoldstino in $γγ+jet$ channel. We have found that this channel is comparable with $γγ$ channel in searches for new physics and deserves further detailed investigations.
We generalize to noncommutative cylinder the solution generation technique, originally suggested for gauge theories on noncommutative plane. For this purpose we construct partial isometry operators and complete set of orthogonal projectors in the algebra of the cylinder, and an isomorphism between the free module and its direct sum with the Fock module on the cylinder. We construct explicitly the gauge theory soliton and evaluate the spectrum of perturbations about this soliton.