Search results for "quantum field"
showing 10 items of 492 documents
Cloud of virtual photons in the ground state of the hydrogen atom.
1985
A spinless, nonrelativistic hydrogen atom coupled to an electromagnetic field is considered. The interaction is taken in the minimal-coupling form, and the ground state of the coupled system is obtained by straightforward perturbation theory. The form of the cloud of virtual photons surrounding the atom is studied through the quantum-mechanical average on this state of an appropriately defined coarse-grained energy-density (CGED) operator W(r\ensuremath{\rightarrow}). The properties of W(r\ensuremath{\rightarrow}) are studied in order to show that this operator can give a reliable description of the shape of the virtual photon cloud. The quantum-mechanical average of W(r\ensuremath{\rightar…
The η transition form factor from space- and time-like experimental data
2015
The $\eta$ transition form factor is analysed for the first time in both space- and time-like regions at low and intermediate energies in a model-independent approach through the use of rational approximants. The $\eta\rightarrow e^+e^-\gamma$ experimental data provided by the A2 Collaboration in the very low energy region of the dilelectron invariant mass distribution allows for the extraction of the most precise up-to-date slope and curvature parameters of the form factors as well as their values at zero and infinity. The impact of these new results on the mixing parameters of the $\eta$-$\eta^\prime$ system, together with the role played by renormalisation dependent effects, and on the d…
Reply to Comment on Measurement of quantum states of neutrons in the Earth's gravitational field
2003
Physical review / D 68(10), 108702 (2003). doi:10.1103/PhysRevD.68.108702
Asymptotic Safety in Quantum Einstein Gravity: Nonperturbative Renormalizability and Fractal Spacetime Structure
2007
The asymptotic safety scenario of Quantum Einstein Gravity, the quantum field theory of the spacetime metric, is reviewed and it is argued that the theory is likely to be nonperturbatively renormalizable. It is also shown that asymptotic safety implies that spacetime is a fractal in general, with a fractal dimension of 2 on sub-Planckian length scales.
Reply to "Comment on `Breakdown of the expansion of finite-size corrections to the hydrogen Lamb shift in moments of charge distribution'"
2016
To comply with the critique of the Comment [J. Arrington, arXiv:1602.01461], we consider another modification of the proton electric form factor, which resolves the "proton-radius puzzle". The proposed modification satisfies all the consistency criteria put forward in the Comment, and yet has a similar impact on the puzzle as that of the original paper. Contrary to the concluding statement of the Comment, it is not difficult to find an ad hoc modification of the form factor at low $Q$ that resolves the discrepancy and is consistent with analyticity constraints. We emphasize once again that we do not consider such an ad hoc modification of the proton form factor to be a solution of the puzzl…
Vacuum induced spin-1/2 Berry's phase.
2002
We calculate the Berry phase of a spin-1/2 particle in a magnetic field considering the quantum nature of the field. The phase reduces to the standard Berry phase in the semiclassical limit and eigenstate of the particle acquires a phase in the vacuum. We also show how to generate a vacuum induced Berry phase considering two quantized modes of the field which has a interesting physical interpretation.
Resonance interaction energy between two accelerated identical atoms in a coaccelerated frame and the Unruh effect
2016
We investigate the resonance interaction energy between two uniformly accelerated identical atoms, interacting with the scalar field or the electromagnetic field in the vacuum state, in the reference frame coaccelerating with the atoms. We assume that one atom is excited and the other in the ground state, and that they are prepared in their correlated symmetric or antisymmetric state. Using perturbation theory, we separate, at the second order in the atom-field coupling, the contributions of vacuum fluctuations and radiation reaction field to the energy shift of the interacting system. We show that only the radiation reaction term contributes to the resonance interaction between the two ato…
Casimir-Polder interatomic potential between two atoms at finite temperature and in the presence of boundary conditions
2007
We evaluate the Casimir-Polder potential between two atoms in the presence of an infinite perfectly conducting plate and at nonzero temperature. In order to calculate the potential, we use a method based on equal-time spatial correlations of the electric field, already used to evaluate the effect of boundary conditions on interatomic potentials. This method gives also a transparent physical picture of the role of a finite temperature and boundary conditions on the Casimir-Polder potential. We obtain an analytical expression of the potential both in the near and far zones, and consider several limiting cases of interest, according to the values of the parameters involved, such as atom-atom d…
Nonperturbative comparison of QCD effective charges
2009
We study the non-perturbative behavior of two versions of the QCD effective charge, one obtained from the pinch technique gluon self-energy, and one from the ghost-gluon vertex. Despite their distinct theoretical origin, due to a fundamental identity relating various of the ingredients appearing in their respective definitions, the two effective charges are almost identical in the entire range of physical momenta, and coincide exactly in the deep infrared, where they freeze at a common finite value. Specifically, the dressing function of the ghost propagator is related to the two form factors in the Lorentz decomposition of a certain Green's function, appearing in a variety of field-theoret…
Branching fraction and form-factor shape measurements of exclusive charmless semileptonicBdecays, and determination of|Vub|
2012
We report the results of a study of the exclusive charmless semileptonic decays, B0→π-l+ν, B+→π0l+ν, B+→ωl+ν, B+→ηl+ν, and B+→η′l+ν (l=e or μ) undertaken with approximately 462×106 BB pairs collected at the Υ(4S) resonance with the BABAR detector. The analysis uses events in which the signal B decays are reconstructed with a loose neutrino reconstruction technique. We obtain partial branching fractions in several bins of q2, the square of the momentum transferred to the lepton-neutrino pair, for B0→π-l+ν, B+→π0l+ν, B+→ωl+ν, and B+→ηl+ν. From these distributions, we extract the form-factor shapes f+(q2) and the total branching fractions B(B0→π-l+ν)=(1.45±0.04stat±0.06syst)×10-4 (combined π- …