118911959
Cold atom clocks, precision oscillators and fundamental tests
We describe two experimental tests of the Equivalence Principle that are based on frequency measurements between precision oscillators and/or highly accurate atomic frequency standards. Based on comparisons between the hyperfine frequencies of 8 7 Rb and 1 3 3 Cs in atomic fountains, the first experiment constrains the variability of fundamental constant. The second experiment is based on a comparison between a cryogenic sapphire oscillator and a hydrogen maser. It tests Local Lorentz Invariance. In both cases, we report recent results which improve significantly over previous experiments.
20986115
Search for variations of fundamental constants using atomic fountain clocks.
Over five years, we have compared the hyperfine frequencies of 133Cs and 87Rb atoms in their electronic ground state using several laser-cooled 133Cs and 87Rb atomic fountains with an accuracy of approximately 10(-15). These measurements set a stringent upper bound to a possible fractional time variation of the ratio between the two frequencies: d/dt ln([(nu(Rb))/(nu(Cs))]=(0.2+/-7.0)x 10(-16) yr(-1) (1sigma uncertainty). The same limit applies to a possible variation of the quantity (mu(Rb)/mu(Cs))alpha(-0.44), which involves the ratio of nuclear magnetic moments and the fine structure constant.
119351516
Zeta Function Method for Repulsive Casimir Forces at Finite Temperature
Instituto de F´isica, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, 21945-970 Rio de Janeiro RJ, Brazil(February 1, 2008)We compute the Casimir energy between an unusual pair of parallel plates at ﬁnite temperature,namely, a perfectely conducting plate (ǫ → ∞) and an inﬁnitely permeable one (µ → ∞) by applyingthe generalized zeta function method. We also compute the Casimir pressure and discuss the highand the low temperature limits.PACS numbers: 35.20.-i.I. INTRODUCTION
18495149
An alternative calculation of the Casimir energy for kappa-deformed electrodynamics
A simple, but effcient way of calculating regularized Casimir energies suitable for non-trivial frequency spectra is briefly described and applied to the case of a kappa-deformed scalar field theory. The results are consistent with the ones obtained by other means.
119571317
On the thermodynamic stability of the modified Chaplygin gas
Abstract This work discusses the thermodynamic stability of an exotic fluid known as modified Chaplygin gas [MCG]. In the literature, one considers such a fluid as a perfect one which obeys the adiabatic equation of state P = B ρ − A / A ρ α , where P stands for the pressure and ρ is the energy density of the fluid; the parameters A and B are positive constants, and α ⩾ 0 . Extending the analysis presented in [F.C. Santos, M.L. Bedran, V. Soares, On the thermodynamic stability of the generalized Chaplygin gas, Phys. Lett. B 636 (2006) 86–90] to the MCG, it is remarked that if the energy density of the Chaplygin fluid in its generalized form ( B = 0 ) or modified form ( B ≠ 0 ) depends on volume only, the temperature of the fluid remains zero at any pressure or volume it may attain. One sets up a scenario to determine the corresponding thermal equation of state of the MCG and it reveals that the MCG only presents thermodynamic stability during any expansion process if its thermal equation of state depends on temperature only, P = P ( T ) . This scenario also establishes physical constraints on the parameters B and α of this equation. Moreover, the modified Chaplygin gas may cool down through any thermodynamic process without facing any critical point or phase transition.