Is the weak interaction constant really constant?

A comparison is made of the probability of the process of two-neutrino double beta decay for ⁸²Se and ⁹⁶Zr in direct (counter) and geochemical experiments. The experimental data for ¹³⁰Te are also analyzed. It is shown that the probability is systematically lower in geochemical experiments, which characterize the probability of (2) decay 10⁹ y ago. It is proposed that this could be due to a change in the weak interaction constant with time. It is proposed that a series of new, precise measurements be performed with the aid of counters and geochemical experiments.     

Large-scale–small-scale duality and the cosmological constant

We study a model of quantum cosmology originating from a classical model of gravitation where a self-interacting scalar field is coupled to gravity with the metric undergoing a signature transition. We show that there are dual classical signature changing solutions, one at large scales and the other at small scales. It is possible to fine-tune the physics in both scales with an infinitesimal effective cosmological constant.     

Time evolution of the cosmological “constant”

We discuss cosmologies where the cosmological constant λ depends on time. The requirements of realistic cosmology impose restrictions on the functional dependence of λ on the Hubble parameter H. We show that for a wide class of functions with λ of the order H³ the system of field equations leads to a stable fix-point behaviour with λ naturally very small today. The age of the universe, critical matter density and deceleration parameter may be modified.     

Small cosmological constant from the QCD trace anomaly?

According to recent astrophysical observations the large scale mean pressure of our present Universe is negative suggesting a positive cosmological constant-like term. The issue of whether nonperturbative effects of self-interacting quantum fields in curved space-times may yield a significant contribution is addressed. Focusing on the trace anomaly of quantum chromodynamics, a preliminary estimate of the expected order of magnitude yields a remarkable coincidence with the empirical data, indicating the potential relevance of this effect.     

Can the baryon number density and the cosmological constant be interrelated?

A toy model is proposed in which the cosmological constant and the baryon number density of the Universe are interrelated. The model combines the mechanism of Dimopoulos and Susskind [S. Dimopoulos, L. Susskind, Phys. Rev. D 18 (1978) 4500] in which the baryon number density of the Universe is generated by the time-dependence of the phase of a complex scalar field, i.e. its ‘angular momentum’ in the two-dimensional complex field space, with that of Yoshimura [M. Yoshimura, Phys. Lett. B 608 (2005) 183, hep-ph/0410183] in which the ‘centrifugal force’ due to the ‘angular momentum’ pushes the vacuum expectation value of the scalar field out of a negative potential minimum and provides a small but positive cosmological constant. Unfortunately, our model fails to relate the smallness of the two numbers directly, requiring a fine-tuning of the negative potential minimum.     

Experimental studies on the multistage constant modulus array for the estimation of directions-of-arrival

The performance of the multistage Constant Modulus (CM) array, one of the most striking blind beamforming algorithms, for the source Directions-of-Arrival (DOA) estimation was analyzed via computer simulations and water tank experiments, and was compared to that of other DOA estimation algorithms including the ‘non-blind‘ and the ‘blind‘. Firstly, a nominal array model and an array model with gain and phase perturbations were established,respectively. Secondly, the multistage CM array algorithm was described and computer simulations were conducted. Simulation results showed that the multistage CM array could correctly estimate the DOA at the same time when the sources were blindly recovered, and the angle separating ability of the algorithm was beyond the Rayleigh resolution limit. By changing the variance of the array model errors, it was also verified that the multistage CM array was more robust to the errors than some other algorithms mentioned in this paper. Finally, water tank experiments and data processing results were provided. Situations with different array sizes and source angular separations were considered. It was shown that the results were in good agreement with computer simulations. Results of computer simulations and water tank experiments verified that the DOAs of the multiple independent sources could be blindly and robustly estimated with the multistage CM array.     

QCD sum rule analysis of the coupling constant g ωσγ

We employ QCD sum rules to calculate the coupling constant g by studying the three point -correlation function. Our result complements the analysis of this coupling constant utilizing the experimental value of the ⁰⁰ decay rate studied within the framework of chiral perturbation theory including vector meson and meson intermediate states.     

Is the electron radiation length constant at high energies?

Experimental results for the radiative energy loss of 149, 207, and 287 GeV electrons in a thin Ir target are presented. From the data we conclude that at high energies the radiation length increases in accordance with the Landau-Pomeranchuk-Migdal (LPM) theory and thus electrons become more penetrating the higher the energy. The increase of the radiation length as a result of the LPM effect has a significant impact on the behavior of high-energy electromagnetic showers.     

Determination of the Avogadro constant – A contribution to the new definition of the mass unit kilogram

An improved attempt of several national metrology institutes to replace the present definition of the kilogram with the mass of a certain number of ¹²C atoms is described. This requires the determination of the Avogadro constant, N _A, via the silicon route with a relative uncertainty better than 2 ⋅ 10^-8. Previously, the limiting factor is the measurement of the average molar mass. Consequently, a world-wide collaboration has been set up, to produce, approximately, 5 kg of ²⁸Si single-crystal with an enrichment factor greater than 99.985% to be used for an improved determination of N _A. The first successful tests of all technological steps (enrichment of SiF₄, purification and synthesis of silane, deposition of polycrystalline ²⁸Si, single crystal growth) for the production of high-purity ²⁸Si are described.     

Can smooth LTB models mimicking the cosmological constant for the luminosity distance also satisfy the age constraint?

The central smoothness of the functions defining a LTB solution plays a crucial role in their ability to mimic the effects of the cosmological constant. Even if non-smoothness is not physically inconsistent with the theory of general relativity, smoothness is still an important geometrical property characterizing the solution of the Einstein’s equations. So far attention has been focused on $C^{1}$ models while in this paper we approach it in a more general way, investigating the implications of higher order central smoothness conditions for LTB models reproducing the luminosity distance of a $\Lambda CDM$ Universe. Our analysis is based on a low red-shift expansion, and extends previous investigations by including also the constraint coming from the age of the Universe and re-expressing the equations for the solution of the inversion problem in a manifestly dimensionless form which makes evident the freedom to accommodate any value of $H_0$ as well. Higher order smoothness conditions strongly limit the number of possible solutions respect to the first order condition. Neither a $C^{1}$ or a $C^{i}$ LTB model can both satisfy the age constraint and mimic the cosmological constant for the luminosity distance. This implies that it is not necessary to include any additional observable to distinguish mathematically the theoretical predictions of a smooth LTB model from a $\Lambda CDM$ . One difference is in the case in which the age constraint is not included and the bang function is zero, in which there is a unique solution for $C^1$ models but no solution for the $C^{i}$ case. Another difference is in the case in which the age constraint is not included and the bang function is not zero, in which the solution is undetermined for both $C^1$ and $C^{i}$ models, but the latter ones have much less residual parametric freedom. Our results imply that any LTB model able to fit luminosity distance data and satisfy the age constraint is either not mimicking exactly the $\Lambda CDM$ red-shift space theoretical predictions or it is not smooth.     

Fedosov observables on constant curvature manifolds and the Klein–Gordon equation

In this paper we construct the Fedosov star-algebra of observables on the phase–space of a single particle in the case of all (finite-dimensional) constant curvature manifolds imbeddable in a flat space with codimension one. This set of spaces includes the two-sphere and de Sitter (dS)/Anti-de Sitter (AdS) space–times. The algebra of observables was constructed by DQ techniques using, in particular, the algorithm provided by Fedosov.     

Measurement of the electronic Grüneisen constant using femtosecond electron diffraction

We report the first accurate measurement of the electronic Grüneisen constant gamma(e) using a novel method employing the new technique of femtosecond electron diffraction. The contributions of the conduction electrons and the lattice to thermal expansion are differentiated in the time domain through transiently heating the electronic temperature well above that of the lattice with femtosecond optical pulses. By directly probing the associated thermal expansion dynamics in real time using femtosecond electron diffraction, we are able to separate the contributions of hot electrons from that of lattice heating, and make an accurate measurement of gamma(e) of aluminum at room temperature. This new approach opens the possibility of distinguishing electronic from magnetic contributions to thermal expansion in magnetic materials at low temperature.     

Some comments on the π-3He-3H coupling constant

Some comments are made on recent determinations of the -³He-³H coupling constant. It is pointed out how the impulse approximation and the elementary particle method treat differently two step processes like radiative pion or muon capture and photo pion production.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.This work is part of the research program of the Stichting FOM, financially supported by the Stichting Z. W. O.     

Dielectric constant of a highly polarizable atomic fluid: the clausius–mossotti versus the onsager relation

The relation between the dielectric constant and the particle polarizability for a polarizable liquid composed of Lennard-Jones particles carrying a saturable induced dipole is studied by computer simulations. It is shown that the widely accepted Clausius–Mossotti relation is only valid for low polarizabilities and fails for high polarizabilities. The results can be fitted accurately by an Onsager-like relation using an effective particle radius measured in the simulations which is larger than the equivalent hard-sphere radius defined conventionally. Furthermore, the orientational ordering transition found at high polarizabilities is shown to be of anti-ferroelectric type.     

Estimation of the QED coupling constant α at\sqrt s = M_Z

LEP measurements of theZ ⁰ parameters have been used to estimate the value of QED coupling constant at theZ ⁰ mass. The estimated value α _eff ^-1 (M _Z )=128.2±0.9 _-0.4 ^+0.0 (M _top) is in good agreement with the expectation of 128.0 _?0.4 ^+0.2 from the Standard Model.     

The NMR indirect nuclear spin–spin coupling constant of the HD molecule

We present new calculated and experimental values of the NMR indirect nuclear spin–spin coupling constant in HD. In the quantum-chemical ab initio calculations, the full configuration-interaction (FCI) method is used, yielding an equilibrium value of 41.22?Hz in the basis-set limit. Adding a calculated zero-point vibrational correction of 1.89?Hz and a temperature correction of 0.20?Hz at 300?K, we obtain a total calculated spin–spin coupling constant of J _FCI(HD)?=?43.31(5)?Hz at 300?K. This result is within the error bars of the experimental gas-phase NMR value, J _exp(HD)?=?43.26(6)?Hz, obtained by extrapolating values measured in HD–He mixtures to zero density.     

The Carter constant and Petrov classification of the Vaidya–Einstein–Kerr spacetime

The existence of the Carter constant in the Vaidya–Einstein–Kerr (VEK) spacetime and its relation to the Petrov type is investigated. This spacetime is an example of a black hole in an asymptotically non-flat background. We construct the Carter constant and obtain the Killing tensor in the VEK spacetime. The Newman–Penrose formalism is employed to obtain the spin coefficients. We present a complete (Petrov) classification of the VEK spacetime and the special case of the non-rotating Vaidya–Einstein–Schwarzschild spacetime. We demonstrate explicitly that both spacetimes are of type-D.     

Casimir effect in the Hořava–Lifshitz gravity with a cosmological constant

We calculate the Casimir energy of a massless scalar field confined between two nearby parallel plates formed by ideal uncharged conductors, placed tangentially to the surface of a sphere with mass M$M$ and radius R$R$. To this end, we take into account a static and spherically symmetric solution of Ho?ava–Lifshitz (HL) gravity, with a cosmological constant term, in lower orders of approximation, considering both weak-field and infrared limits. We show that the Casimir energy, just in the second order weak-field approximation, is modified due to the parameter of the HL gravity as well as to the cosmological constant.