14322904
QED vacuum between an unusual pair of plates
We consider the photon field between an unusual configuration of infinite parallel plates: a perfectly conducting plate (ǫ → ∞) and an infinitely permeable one μ → ∞). After quantizing the vector potential in the Coulomb gauge, we obtain explicit expressions for the vacuum expectation values of field operators of the form < ÊiÊj >0 and < B̂iB̂j >0. These field correlators allow us to reobtain the Casimir effect for this set up and to discuss the light velocity shift caused by the presence of plates (Scharnhorst effect [1, 2, 3]) for both scalar and spinor QED. PACS numbers: 11.10.-z, 11.10.Mn
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.
122987994
Lie symmetries for the charge-monopole problem
The authors obtain the Lie symmetries for the equation of motion of an electric charge interacting with a magnetic monopole, fixed at the origin. They also discuss the construction of first integrals for this problem.
18610535
Confined Maxwell Field and Temperature Inversion Symmetry
We evaluate the Casimir vacuum energy at finite temperature associated with the Maxwell field confined by a perfectly conducting rectangular cavity and show that an extended version of the temperature inversion symmetry is present in this system.
120560609
Properties of a general-relativistic kink solution
Properties of the general-relativistic kink solution of a nonlinear scalar field recently obtained are discussed. It has been shown that the kink solution is stable against radial perturbations. Possible applications to hadron physics from the geometrodynamic point of view are suggested.
117047855
The Casimir energy of a massive fermion field revisited
We introduce a general, simple and effective method of evaluating the zero point energy of a quantum field under the influence of arbitrary boundary conditions imposed on the field on flat surfaces perpendicular to a chosen spatial direction. As an example we apply the method to the Casimir effect associated with a massive fermion field on which MIT bag model type of boundary conditions are imposed.
118628741
Gupta-Bleuler quantization of the anisotropic parity-even and C P T -even electrodynamics of a standard model extension
We have established the Gupta-Bleuler quantization of the photon belonging to the anisotropic parity-even sector of the CPT-even and Lorentz-violating nonbirefringent electrodynamics of the standard model extension. We first present a rule for the Maxwell electrodynamics to be successfully quantized via Gupta-Bleuler technique in the Lorentz gauge. Recognizing the failure of the Gupta-Bleuler method in the Lorentz gauge, $\partial _{\mu }A^{\mu }=0$, for this massless LV theory, we argue that Gupta-Bleuler can be satisfactorily implemented by choosing a modified Lorentz condition, $\partial _{\mu }A^{\mu }+\kappa ^{\mu \nu }\partial _{\mu }A_{\nu }=0$, where $\kappa ^{\mu \nu }$ represents the Lorentz-violation in photon sector. By using a plane-wave expansion for the gauge field, whose polarization vectors are determined by solving an eigenvalue problem, and a weak Gupta-Bleuler condition, we obtain a positive-energy Hamiltonian in terms of annihilation and creation operators. The field commutation relation is written in terms of modified Pauli-Jordan functions, revealing the preservation of microcausality for sufficiently small LV parameters.
17807895
Neutrino helicity asymmetries in leptogenesis
It is pointed out that the heavy singlet neutrinos characteristic of leptogenesis develop asymmetries in the abundances of the two helicity states as a result of the same mechanism that generates asymmetries in the standard lepton sector. Neutrinos and standard leptons interchange asymmetries in collisions with each other. It is shown that an appropriate quantum number, B-L{sup '}, combining baryon, lepton and neutrino asymmetries, is not violated as fast as the standard B-L. This suppresses the washout effects relevant for the derivation of the final baryon asymmetry. One presents detailed calculations for the period of neutrino thermal production in the framework of the singlet seesaw mechanism.
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.