Trending Papers in physics

A model for a cyclic big bang as the result of a giant cosmic firewall is conjectured in this white paper.

The article describes various aspects of mathematical modeling of fluidflows, both in general and with reference to hydraulic machinery. The articlereviews historical development of corresponding methods of mathematicalmodeling. Implementation of these aspects in modern commercial CFD softwaretools is described together with advantages and disadvantages of implementedmethods. The conclusion is drawn concerning possibilities of computation offluid flows nowadays.

We study the numerical solution of the non-relativistic Schr\"{o}dingerequation for two-electron atoms in ground and excited S-states usingpseudospectral (PS) methods of calculation. The calculation achievesconvergence rates for the energy, Cauchy error in the wavefunction, andvariance in local energy that are exponentially fast for all practicalpurposes. The method requires three separate subdomains to handle thewavefunction's cusp-like behavior near the two-particle coalescences. The useof three subdomains is essential to maintaining exponential convergence. Acomparison of several different treatments of the cusps and the semi-infinitedomain suggest that the simplest prescription is sufficient. For many purposesit proves unnecessary to handle the logarithmic behavior near thethree-particle coalescence in a special way. The PS method has many virtues: noexplicit assumptions need be made about the asymptotic behavior of thewavefunction near cusps or at large distances, the local energy is exactlyequal to the calculated global energy at all collocation points, local errorsgo down everywhere with increasing resolution, the effective basis usingChebyshev polynomials is complete and simple, and the method is easilyextensible to other bound states. This study serves as a proof-of-principle ofthe method for more general two- and possibly three-electron applications.

Invisible psi and Upsilon decays into light neutralinos, within the MSSM orN(n)MSSM, are smaller than for nu nubar production, even if light spin-0particles are coupled to quarks and neutralinos. In a more general way, lightdark matter particles are normally forbidden, unless they can annihilatesufficiently through a new interaction stronger than weak interactions (atlower energies), as induced by a light spin-1 U boson, or heavy-fermionexchanges in the case of scalar dark matter. We discuss the possiblecontributions of U-boson, heavy-fermion, or spin-0 exchanges to invisible psiand Upsilon decays. U-exchanges could lead, but not necessarily, to significant branchingfractions for invisible decays into light dark matter. We show how one can getthe correct relic density together with sufficiently small invisible branchingfractions, and the resulting constraints on the U couplings to ordinaryparticles and dark matter, in particular |c_chi.f_bV| < 5 10^-3 from Upsilondecays, for 2 m_chi smaller than a few GeV. We also explain why there is nomodel-independent way to predict psi and Upsilon branching fractions into lightdark matter, from dark matter annihilation cross sections at freeze-out time.

We consider the possibility that the Higgs can be produced in dark matterannihilations, appearing as a line in the spectrum of gamma rays at an energydetermined by the masses of the WIMP and the Higgs itself. We argue that thisphenomenon occurs generally in models in which the the dark sector has largecouplings to the most massive states of the SM and provide a simple exampleinspired by the Randall-Sundrum vision of dark matter, whose 4d dualcorresponds to electroweak symmetry-breaking by strong dynamics which respectglobal symmetries that guarantee a stable WIMP. The dark matter is a Diracfermion that couples to a Z' acting as a portal to the Standard Model throughits strong coupling to top quarks. Annihilation into light standard modeldegrees of freedom is suppressed and generates a feeble continuum spectrum ofgamma rays. Loops of top quarks mediate annihilation into gamma Z, gamma h, andgamma Z', providing a forest of lines in the spectrum. Such models can beprobed by the Fermi/GLAST satellite and ground-based Air Cherenkov telescopes.

The Fisher Ideal index, developed to measure price inflation, is applied todefine a population-weighted temperature trend. This method has the advantagesthat the trend is representative for the population distribution throughout thesample but without conflating the trend in the population distribution and thetrend in the temperature. I show that the trend in the global area-weightedaverage surface air temperature is different in key details from thepopulation-weighted trend. I extend the index to include urbanization and theurban heat island effect. This substantially changes the trend again. I furtherextend the index to include international migration, but this has a minorimpact on the trend.