Search results for "Coupling"
showing 10 items of 1862 documents
Towards a precision calculation of the effective number of neutrinos đ_đžđżđż in the Standard Model. Part II. Neutrino decoupling in the presence ofâŚ
2021
Abstract We present in this work a new calculation of the standard-model benchmark value for the effective number of neutrinos, Neff SM, that quantifies the cosmological neutrino-to-photon energy densities. The calculation takes into account neutrino flavour oscillations, finite-temperature effects in the quantum electrodynamics plasma to O(e3), where e is the elementary electric charge, and a full evaluation of the neutrino-neutrino collision integral. We provide furthermore a detailed assessment of the uncertainties in the benchmark Neff SM value, through testing the value's dependence on (i) optional approximate modelling of the weak collision integrals, (ii) measurement errors in the phâŚ
Atomic Ionization by Scalar Dark Matter and Solar Scalars
2021
We calculate the cross-sections of atomic ionization by absorption of scalar particles in the energy range from a few eV to 100 keV. We consider both nonrelativistic particles (dark matter candidates) and relativistic particles which may be produced inside Sun. We provide numerical results for atoms relevant for direct dark matter searches (O, Na, Ar, Ca, Ge, I, Xe, W and Tl). We identify a crucial flaw in previous calculations and show that they overestimated the ionization cross sections by several orders of magnitude due to violation of the orthogonality of the bound and continuum electron wave functions. Using our computed cross-sections, we interpret the recent data from the Xenon1T exâŚ
Electromagnetically induced transparency resonances inverted in magnetic field
2015
The electromagnetically induced transparency (EIT) phenomenon has been investigated in a $\Lambda$-system of the $^{87}$Rb D$_1$ line in an external transverse magnetic field. Two spectroscopic cells having strongly different values of the relaxation rates $\gamma_{rel}$ are used: a Rb cell with antirelaxation coating ($L\sim$1 cm) and a Rb nanometric-thin cell (nano-cell) with thickness of the atomic vapor column $L$=795nm. For the EIT in the nano-cell, we have the usual EIT resonances characterized by a reduction in the absorption (i.e. dark resonance (DR)), whereas for the EIT in the Rb cell with an antirelaxation coating, the resonances demonstrate an increase in the absorption (i.e. brâŚ
Hyperfine interaction in the Autler-Townes effect: The formation of bright, dark, and chameleon states
2017
This paper is devoted to clarifying the implications of hyperfine (HF) interaction in the formation of adiabatic (i.e., ``laser-dressed'') states and their expression in the Autler-Townes (AT) spectra. We first use the Morris-Shore model [J. R. Morris and B. W. Shore, Phys. Rev. A 27, 906 (1983)] to illustrate how bright and dark states are formed in a simple reference system where closely spaced energy levels are coupled to a single state with a strong laser field with the respective Rabi frequency ${\mathrm{\ensuremath{\Omega}}}_{S}$. We then expand the simulations to realistic hyperfine level systems in Na atoms for a more general case when non-negligible HF interaction can be treated asâŚ
Analyzing dynamical gluon mass generation
2007
We study the necessary conditions for obtaining infrared finite solutions from the Schwinger-Dyson equation governing the dynamics of the gluon propagator. The equation in question is set up in the Feynman gauge of the background field method, thus capturing a number of desirable features. Most notably, and in contradistinction to the standard formulation, the gluon self-energy is transverse order-by-order in the dressed loop expansion, and separately for gluonic and ghost contributions. Various subtle field-theoretic issues, such as renormalization group invariance and regularization of quadratic divergences, are briefly addressed. The infrared and ultraviolet properties of the obtained soâŚ
Observation of Coulomb-Assisted Nuclear Bound State of ÎââN14 System
2021
In an emulsion-counter hybrid experiment performed at J-PARC, a Î^{-} absorption event was observed which decayed into twin single-Î hypernuclei. Kinematic calculations enabled a unique identification of the reaction process as Î^{-}+^{14}Nâ_{Î}^{10}Be+_{Î}^{5}He. For the binding energy of the Î^{-} hyperon in the Î^{-}-^{14}N system a value of 1.27Âą0.21ââMeV was deduced. The energy level of Î^{-} is likely a nuclear 1p state which indicates a weak ÎN-ÎÎ coupling.
Biogeochemical decoupling: how, where and when?
2018
Research has dealt with coupling of chemical element cycles and feedback in recent years. Sometimes, this biogeochemical coupling is reversed through abiotic or biotic (including man-made) processes. It is then called biogeochemical decoupling and is a disconnection between two chemical elements whereby transformations of one affect cycling of the other, and results in asynchronical behavior of chemical elements. It appears to be more important and widespread than earlier reports suggest, and gives rise to important changes in element stoichiometry of resources. These changes in turn modify organismal stoichiometry that, if great enough, can affect biodiversity and food webs, thus altering âŚ
Experimental and theoretical study of band structure of InSe andIn1âxGaxSe(x<0.2)under high pressure:âDirect to indirect crossovers
2001
This paper reports on the pressure dependence of the absorption edge of indium selenide and ${\mathrm{In}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}\mathrm{Se}$ alloys $(xl0.2)$ up to the pressure at which precursor effects of the phase transition prevent further transmission measurements. The absorption edge could be divided into three components exhibiting different pressure coefficients: one corresponding to a direct transition that could be analyzed through the Elliot-Toyozawa theory, and two supplementary edges with quadratic dependence on the photon energy. The first component is attributed to the direct transition at the Z point of the rhombohedral Brillouin zone. One of the quadratic absoâŚ
Analytical and numerical analysis of the atomâfield dynamics in non-stationary cavity QED
2011
We study analytically and numerically the dynamics of the quantum non-stationary system composed of a two-level atom interacting with a single mode cavity field whose frequency is rapidly modulated in time (with a small amplitude). We identify modulation laws resulting in qualitatively different dynamical regimes and we present analytical solutions in some simple cases. In particular, we analyse minutely the influence of the fieldâatom coupling on the photon generation from vacuum via the dynamical Casimir effect.
From kinks to compactonlike kinks
1998
We show that, in the continuum limit, the generalized \ensuremath{\Phi}-four or double-well model with nonlinear coupling can exhibit compactonlike kink solutions for some specific velocity regimes and when the nonlinear coupling between pendulums is dominant. Our numerical simulations point out that the static compacton is stable and the dynamic compacton is unstable. Our study is extended to other topological systems where compacton solutions can also be found. A nice feature is that a mechanical analog of the double-well system can be constructed in the form of an experimental lattice of coupled pendulums, which, in the strong coupling limit, allows the observation of these entities.