We calculate the signal rate of hypothetical heavy neutral leptons (HNL or sterile neutrinos) from kaon decays expected in the framework of the SHiP experiment. The kaons are produced in the hadronic ...shower initiated in the beam-dump mode by 400 GeV protons from CERN SPS. For a sufficiently light HNL (when the decays are kinematically allowed) we find kaon decays to be a noticeably richer source of HNL as compared to D-meson decays adopted in previous studies of the HNL phenomenology at SHiP. In particular, SHiP is capable of fully exploring the central part of the kinematically allowed region of the HNL mass and mixing with electron and muon neutrinos down to the lower cosmological bound. The latter is associated with HNL decays in the early Universe to energetic products rescattering off and thus destroying light nuclei produced at the primordial nucleosynthesis. A consistency of the HNL model with smaller mixing would require either a hierarchy – much larger mixing of all the HNL with tau neutrino – or non-standard cosmology and new ingredients in the HNL sector, closing the room for the minimal non-seesaw type I model with sterile neutrinos lighter than kaons.
We argue that the fixed target experiment PS191 operating on a proton beam of 19.2 GeV at CERN in the eighties was sensitive to hypothetical light scalars produced by mesons and decaying to charged ...particles. The experiment was dedicated to searches for sterile neutrinos produced in weak meson decays and decaying into final states with pairs of charged particles: electrons and muons. Two charged tracks from the same point have been adopted as the signal signature. Exploiting the same signature we use the negative results of searches at PS191 and place new limits on the light scalars coupled to the Standard Model (SM) particles via mixing with the Higgs boson. In particular, previously allowed region of masses 100–150 MeV and mixing above 4×10−4 is disfavored. Our analysis can be extended straightforwardly to models with other patterns of scalar couplings to SM particles.
We perform Monte Carlo simulations of the sterile neutrino signal at the fixed target experiment PS191 operated on a proton beam of 19.2GeV at CERN in the eighties. We find that the strongest bounds ...the PS191 could obtain are significantly lower than what they published, and now are obsolete being surpassed by recent T2K, NA62, E949, TRIUMF and PIENU experiments.
We calculate the production of hypothetical millicharged particles (MCPs) of sub-GeV masses by the J-PARC proton beam in the framework of T2K and future T2HK neutrino oscillation experiments. ...Concentrating on the region of model parameter space, where an MCP can hit the near neutrino detector twice, we adopt this background-free signature to estimate the sensitivity of T2K and T2HK experiments to MCPs. We find that a previously inaccessible in direct searches region of charges 5×10−4-10−2e for MCP masses 0.1-0.5 GeV can be probed.
Seesaw mechanism constrains from below mixing between active and sterile neutrinos for fixed sterile neutrino masses. Signal events associated with sterile neutrino decays inside a detector at fixed ...target experiment are suppressed by the mixing angle to the power of four. Therefore sensitivity of experiments such as SHiP and DUNE should take into account minimal possible values of the mixing angles. We extend the previous study of this subject 1 to a more general case of non-zero CP-violating phases in the neutrino sector. Namely, we provide numerical estimate of minimal value of mixing angles between active neutrinos and two sterile neutrinos with the third sterile neutrino playing no noticeable role in the mixing. Thus we obtain a sensitivity needed to fully explore the seesaw type I mechanism for sterile neutrinos with masses below 2 GeV, and one undetectable sterile neutrino that is relevant for the fixedtarget experiments. Remarkably, we observe a strong dependence of this result on the lightest active neutrino mass and the neutrino mass hierarchy, not only on the values of CP-violating phases themselves. All these effects sum up to push the limit of experimental confirmation of sterile-active neutrino mixing by several orders of magnitude below the results of 1 from 10
-10
- 10
-11
down to 10
-12
and even to 10
-20
in parts of parameter space; non-zero CP-violating phases are responsible for that.
Metastable ion Coulomb crystal (ICC) in the polychromatic optical superlattice (OSL) created by so-called rectified gradient forces is studied. Our analysis is based on the numerical solution of the ...nonlinear stochastic differential equations taking into account the trapping and dissipative forces, their quantum fluctuations, and Coulomb repulsion of ions. The key question is how long will this metastable highly ordered crystalline structure persist. The critical parameter determining the ICC destruction times
t
d
is the OSL period
L
(at fixed intensity values of the optical fields). Our simulations demonstrate that
t
d
of the ICC, consisting of several tens of mercury ions, experiences giant changes (by four orders of magnitude) at relatively slight variations of the optical superlattice period
L
in the range from 0.35 to 0.70 mm. We have shown that the dependence t
d
(
L
) can be approximated by the Arrhenius-like equation with an effective activation energy which is nonlinearly dependent on the OSL period
L
. These results explain the ultrahigh sensitivity t
d
(
L
) to the OSL period
L
and show how to adjust
L
to ensure all-optical confinement of ICC in the OSL from a fraction of a second to one and half minutes.
Graphical abstract
Using an in situ combination of tensile tests and x-ray diffraction, we have determined the mechanical properties of both the crystalline and the disordered phase of the biological nanocomposite silk ...by adapting a model from linear viscoelastic theory to the semicrystalline morphology of silk. We observe a strong interplay between morphology and mechanical properties. Silk's high extensibility results principally from the disordered phase; however, the crystals are also elastically deformed.
The aim of the work was to analyse changes in the location and morphological characteristics of calbindin (CB)-immunoreactive (IR) neurons of the thoracic spinal cord of C57BL/6N male mice after ...completion of a 30-day space flight on board the BION-M1 biosatellite (Russia, 2013). Space flight induced multidirectional changes of the number and morphological parameters of CB-positive neurons. The number of IR neurons increased in laminae I (from 10 to 17 neurons per section), II (from 42 to 67 cells per section) and IX (from two neurons per segment to two neurons per section), but CB disappeared in neurons of lamina VIII. Weightlessness did not affect the number of CB-IR neurons in laminae III–V and VII, including preganglionic sympathetic neurons. The cross-sectional area of CB-IR neurons decreased in lamina II and VII (group of partition cells) and increased in laminae III–V and IX. After a space flight, few very large neurons with long dendrites appeared in lamina IV. The results obtained give evidence about substantial changes in the calcium buffer system and imbalance of different groups of CB-IR neurons due to reduction of afferent information under microgravity.
Metastable ion Coulomb crystal (ICC) in the polychromatic optical superlattice (OSL) created by so-called rectified gradient forces is studied. Our analysis is based on the numerical solution of the ...nonlinear stochastic differential equations taking into account the trapping and dissipative forces, their quantum fluctuations, and Coulomb repulsion of ions. The key question is how long will this metastable highly ordered crystalline structure persist. The critical parameter determining the ICC destruction times td is the OSL period L (at fixed intensity values of the optical fields). Our simulations demonstrate that td of the ICC, consisting of several tens of mercury ions, experiences giant changes (by four orders of magnitude) at relatively slight variations of the optical superlattice period L in the range from 0.35 to 0.70 mm. We have shown that the dependence td (L) can be approximated by the Arrhenius-like equation with an effective activation energy which is nonlinearly dependent on the OSL period L. These results explain the ultrahigh sensitivity td (L) to the OSL period L and show how to adjust L to ensure all-optical confinement of ICC in the OSL from a fraction of a second to one and half minutes.
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