Search

The crystal structure and magnetic properties of the multicomponent Laves phase compounds (Gd1-xYx)0.8Sm0.2Fe2Hz ($\boldsymbol{x}$ = 0, 0.2, 0.4, 0.6, 0.8, 1; $\boldsymbol{z}$ = 0 and 3.4) are investigated. These compounds crystallize into an MgCu2 type of structure. Hydrogenation does not change the crystal structure type but boosts the unit cell volume of (Gd,Y,Sm)Fe2 by ∼25%. Both parent and the hydrogen-charged ferrimagnetic compounds demonstrate magnetic compensation (mutual cancellation of magnetic moments of the individual magnetic sublattices). The exact compositions with zero magnetization state (compensated compositions) predicted using a three-sublattice model are in good agreement with the experiment. In the hydrides, the magnetic compensation takes place at a lower Y content as compared to the parent alloys. Pulsed magnetic fields reveal a distinctly different behavior of magnetization in the hydrides. With the increase of magnetic field, magnetization increases much faster in the hydrides as compared to the parent compounds.

Considering the supersymmetric models with light neutralino and /?-parity violation, we perform estimates of the signal rate expected at the recently proposed fixed target SHiP experiment exploiting the CERN SPS beam of 400 GeV protons. We extend the existing studies by introducing new production channels (in particular, through the beauty mesons) and decay modes. We also constrain the model parameter space from analysis of negative results of the CHARM experiment. [ABSTRACT FROM AUTHOR]

For the extension of the Standard Model with light hidden photons, we present preliminary estimates of the signal rate expected at the recently proposed fixed target SHiP experiment exploiting the CERN SPS beam of 400 GeV protons. [ABSTRACT FROM AUTHOR]

We consider collider signatures of the hylogenesis--a variant of the 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Introducing new fermions into particles physics that are singlet under the gauge group of the Standard Model allows using the seesaw type-I mechanism to obtain small neutrino masses and explaining the phenomenon of neutrino oscillations. The mass scale of these fermions (sterile neutrinos) is a free parameter with values ranging widely from a subelectronvolt to $ 10^{15}$ GeV. The mass scale determines the direct search strategy for these particles, and depending on it, sterile neutrinos can influence the evolution of the Universe and can be responsible for the baryon asymmetry of the Universe and for the phenomenon of dark matter.

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, &mtilde;2LL and &mtilde;2RR. We find that present limits on off-diagonal entries in squark and slepton squared mass matrices allow t-, b-, c-quark and T-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→ cSP) &lsim;< 10-7, Br(T→μSP) &lsim; 10-7, Br(5s → SP) =&lsim; 10-4, Br(B → K(*)SP) &lsim; 10-4, Br(D → SP) &lsim; 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. [ABSTRACT FROM AUTHOR]

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 estimate 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. [ABSTRACT FROM AUTHOR]

The interaction of 3, 5-di-tert-butyl-4-hydroxy-N, N-dimethylbenzyiamine with various acyl halides has been studied. The N-acyl quaternary ammonium salts obtained can be used to introduce a sterically hindered phenol fragment into organic compounds containing an active methylene group.

The reactions of the quaternary acylammonium salt formed on treatment of3,5-di-tertbutyl-4-hydroxy N,N-dimethylbenzylamine with acetyl chloride, with various organic and inorganic sulfur-containing compounds were studied. The possibility of using this salt for the introduction of a sterically hindered phenol moiety in various sulfur-containing compounds was shown.

Cosmic rays bombard the lunar surface producing mesons, which attenuate inside the regolith. They get slower and decay weakly into mostly sub-GeV neutrinos leaving the surface. Thus the Moon shines in neutrinos. Here we calculate spectra of low-energy neutrinos, which exhibit bright features potentially recognizable above isotropic neutrino background in the direction towards the Moon. Their observation, though a very challenging task for future neutrino large volume experiments, would make the Moon the nearest astrophysical source for which the concept of multimessenger astronomy truly works. Remarkably, some features of the lunar neutrino flux are sensitive to the surface mass density of the Moon. [ABSTRACT FROM AUTHOR]

It has been recently suggested [1] that a subdominant fraction of dark matter decaying after recombination may alleviate tension between high-redshift (CMB anisotropy) and low-redshift (Hubble constant, cluster counts) measurements. In this report, we continue our previous study [2] of the decaying dark matter (DDM) model adding all available recent baryon acoustic oscillation (BAO) and redshift space distortions (RSD) measurements. We find that the BAO/RSD measurements generically prefer the standard ΛCDM and combined with other cosmological measurements impose an upper limit on the DDM fraction at the level of ∼5%, strengthening by a factor of 1.5 limits obtained in [2] mostly from CMB data. However, the numbers vary from one analysis to other based on the same Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12 (DR12) galaxy sample. Overall, the model with a few percent DDM fraction provides a better fit to the combined cosmological data as compared to the ΛCDM: the cluster counting and direct measurements of the Hubble parameter are responsible for that. The improvement can be as large as 1.5σ and grows to 3.3σ when the CMB lensing power amplitude AL is introduced as a free fitting parameter. [ABSTRACT FROM AUTHOR]

We investigate the prospects of the Spectrum-Roentgen-Gamma (SRG) mission in search for the keV-scale mass sterile neutrino dark matter radiatively decaying into active neutrinos and photons. The ongoing all-sky x-ray survey of the SRG space observatory with data acquired by the ART-XC and eROSITA telescopes can provide a possibility to fully explore the resonant production mechanism of the dark matter sterile neutrino, which exploits the lepton asymmetry in the primordial plasma consistent with cosmological limits from the big bang nucleosynthesis. In particular, it is shown that at the end of the four year all-sky survey, the sensitivity of the eROSITA telescope near the 3.5 keV line signal reported earlier can be comparable to that of the XMM-Newton with all collected data, which will allow one to carry out another independent study of the possible sterile neutrino decay signal in this area. In the energy range below ≈2.4 keV, the expected constraints on the model parameters can be significantly stronger than those obtained with the XMM-Newton. From the ART-XC data, in the energy range approximately from 5 to 20 keV, it can be possible to get more stringent constraints than those obtained with NuSTAR so far. We conclude that the SRG mission has a very high potential in testing the sterile neutrino dark matter hypothesis. [ABSTRACT FROM AUTHOR]

It has been recently suggested [F. Bezrukov et al. J. Cosmol. Astropart. Phys. 06 (2017) 051; F. Bezrukov et al. Phys. Rev. D 99, 083507 (2019)] that a cosmic scalar field can completely change the keV-scale sterile neutrino production in the early Universe. Its effect may, for various parameter choices, either suppress sterile neutrino production and make moderate active-sterile mixing cosmologically acceptable, or increase the production and generate a considerable dark matter component out of sterile neutrino with otherwise negligible mixing with SM. In this paper, we provide analytic estimates complementing and improving of the numerical calculations performed by F. Bezrukov et al. [Phys. Rev. D 99, 083507 (2019) in the case of the resonant amplification of the sterile neutrino production by the scalar field. We found the substantially cooler velocity distribution of sterile neutrinos as compared to most production mechanisms, opening a new window for warm dark matter, which is otherwise forbidden by structure formation considerations. We also discuss phenomenological and theoretical issues related to the successful implementation of this idea in fully realistic extensions of the Standard Model of particle physics. [ABSTRACT FROM AUTHOR]

We describe two new generation mechanisms for dark matter (DM) composed of sterile neutrinos with O(1) keV mass. The model contains a light scalar field that coherently oscillates in the early Universe and modulates the Majorana mass of the sterile neutrino. In a region of model parameter space, the oscillations between active and sterile neutrinos are resonantly enhanced. This mechanism allows us to produce sterile neutrino DM with a small mixing angle with active neutrinos, thus evading the x-ray constraints. At the same time, the spectrum of produced DM is much cooler than in the case of ordinary oscillations in plasma, opening a window of lower mass DM, which is otherwise forbidden by structure formation considerations. In other regions of the model parameter space, where the resonance does not appear, another mechanism can operate: a large field suppresses the active-sterile oscillations, but instead sterile neutrinos are produced by the oscillating scalar field when the effective fermion mass crosses zero. In this case, the DM component is cold, and even the 1 keV neutrino is consistent with the cosmic structure formation. [ABSTRACT FROM AUTHOR]