Moscow State University

About: Moscow State University is a education organization based out in Moscow, Russia. It is known for research contribution in the topics: Laser & Population. The organization has 66747 authors who have published 123358 publications receiving 1753995 citations. The organization is also known as: MSU & Lomonosov Moscow State University.

Constraints on primordial black holes as dark matter candidates from capture by neutron stars

Abstract: We investigate constraints on primordial black holes (PBHs) as dark matter candidates that arise from their capture by neutron stars (NSs). If a PBH is captured by a NS, the star is accreted onto the PBH and gets destroyed in a very short time. Thus, mere observations of NSs put limits on the abundance of PBHs. High DM densities and low velocities are required to constrain the fraction of PBHs in DM. Such conditions may be realized in the cores of globular clusters if the latter are of a primordial origin. Assuming that cores of globular clusters possess the DM densities exceeding several hundred $\mathrm{GeV}/{\mathrm{cm}}^{3}$ would imply that PBHs are excluded as comprising all of the dark matter in the mass range $3\ifmmode\times\else\texttimes\fi{}{10}^{18}\ensuremath{\lesssim}{m}_{\mathrm{BH}}\ensuremath{\lesssim}{10}^{24}\text{ }\text{ }\mathrm{g}$. At the DM density of $2\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }\text{ }\mathrm{GeV}/{\mathrm{cm}}^{3}$ that has been found in simulations in the corresponding models, less than 5% of the DM may consist of PBH for these PBH masses.

Relativistic and charge-displacement self-channeling of intense ultrashort laser pulses in plasmas

Abstract: Relativistic and charge-displacement self-channeling is one of the most significant phenomena in the entire area of the interactions of extremely intense laser pulses with matter. Both the relativistic increase in the mass of laserdriven plasma electrons and the reduction of electron concentration under the effect of the ponderomotive force tend to reduce the local electron frequency in a laser-irradiated plasma. As a result, the simultaneous modification of the plasma dielectric response by the propagating electromagnetic radiation via the above two mechanisms enhances the medium transparency in the paraxial domain where the intensity is maximal. Under certain conditions discussed in this chapter, this effect leads to the emergence of channeled regimes of superintense laser pulse propagation in underdense plasmas. In these regimes, the laser radiation diffraction is suppressed, nonlinear beam self-trapping occurs, and the laser pulse propagates into the plasma over dozens of Rayleigh ranges. An additional electromagnetic radiation confinement mechanism emerges due to electron cavitation, namely, the total expulsion of the electron fluid from a certain spatial area. Then, the laser beam propagates within the resulting channel, where the intensities can reach the level of 1022 W/cm2.

Measurement of Higgs boson production in the diphoton decay channel in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector

Abstract: A measurement of the production processes of the recently discovered Higgs boson is performed in the two-photon final state using 4.5 fb(-1) of proton-proton collisions data at root s = 7 TeV and 20.3 fb(-1) at root s = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. The number of observed Higgs boson decays to diphotons divided by the corresponding Standard Model prediction, called the signal strength, is found to be mu = 1.17 +/- 0.27 at the value of the Higgs boson mass measured by ATLAS, m(H) = 125.4 GeV. The analysis is optimized to measure the signal strengths for individual Higgs boson production processes at this value of m(H). They are found to be mu(ggF) = 1.32 +/- 0.38, mu(VBF) = 0.8 +/- 0.7, mu(WH) = 1.0 +/- 1.6, mu(ZH) = 0.1(-0.1)(+3.7), and mu t (t) over barH = 1.6(-1.8)(+2.7), for Higgs boson production through gluon fusion, vector-boson fusion, and in association with a W or Z boson or a top-quark pair, respectively. Compared with the previously published ATLAS analysis, the results reported here also benefit from a new energy calibration procedure for photons and the subsequent reduction of the systematic uncertainty on the diphoton mass resolution. No significant deviations from the predictions of the Standard Model are found.

Strong interplay between stripe spin fluctuations, nematicity and superconductivity in FeSe

Abstract: In iron-based superconductors the interactions driving the nematic order (that breaks four-fold rotational symmetry in the iron plane) may also mediate the Cooper pairing. The experimental determination of these interactions, which are believed to depend on the orbital or the spin degrees of freedom, is challenging because nematic order occurs at, or slightly above, the ordering temperature of a stripe magnetic phase. Here, we study FeSe (ref. )-which exhibits a nematic (orthorhombic) phase transition at Ts = 90 K without antiferromagnetic ordering-by neutron scattering, finding substantial stripe spin fluctuations coupled with the nematicity that are enhanced abruptly on cooling through Ts. A sharp spin resonance develops in the superconducting state, whose energy (∼4 meV) is consistent with an electron-boson coupling mode revealed by scanning tunnelling spectroscopy. The magnetic spectral weight in FeSe is found to be comparable to that of the iron arsenides. Our results support recent theoretical proposals that both nematicity and superconductivity are driven by spin fluctuations.