38 research outputs found
Shapiro Effect as a Possible Cause of the Low-Frequency Pulsar Timing Noise in Globular Clusters
A prolonged timing of millisecond pulsars has revealed low-frequency
uncorrelated noise, presumably of astrophysical origin, in the pulse arrival
time (PAT) residuals for some of them. In most cases, pulsars in globular
clusters show a low-frequency modulation of their rotational phase and spin
rate. The relativistic time delay of the pulsar signal in the curved space time
of randomly distributed and moving globular cluster stars (the Shapiro effect)
is suggested as a possible cause of this modulation.
Given the smallness of the aberration corrections that arise from the
nonstationarity of the gravitational field of the randomly distributed ensemble
of stars under consideration, a formula is derived for the Shapiro effect for a
pulsar in a globular cluster. The derived formula is used to calculate the
autocorrelation function of the low-frequency pulsar noise, the slope of its
power spectrum, and the behavior of the statistic that characterizes
the spectral properties of this noise in the form of a time function. The
Shapiro effect under discussion is shown to manifest itself for large impact
parameters as a low-frequency noise of the pulsar spin rate with a spectral
index of n=-1.8 that depends weakly on the specific model distribution of stars
in the globular cluster. For small impact parameters, the spectral index of the
noise is n=-1.5.Comment: 23 pages, 6 figure
Gravitational Couplings of Intrinsic Spin
The gravitational couplings of intrinsic spin are briefly reviewed. A
consequence of the Dirac equation in the exterior gravitational field of a
rotating mass is considered in detail, namely, the difference in the energy of
a spin-1/2 particle polarized vertically up and down near the surface of a
rotating body is . Here is the latitude and
, where and are, respectively, the angular
momentum and radius of the body. It seems that this relativistic quantum
gravitational effect could be measurable in the foreseeable future.Comment: LaTeX file, no figures, 16 page
Neutrino oscillations and uncertainty relations
We show that coherent flavor neutrino states are produced (and detected) due
to the momentum-coordinate Heisenberg uncertainty relation. The Mandelstam-Tamm
time-energy uncertainty relation requires non-stationary neutrino states for
oscillations to happen and determines the time interval (propagation length)
which is necessary for that. We compare different approaches to neutrino
oscillations which are based on different physical assumptions but lead to the
same expression for the neutrino transition probability in standard neutrino
oscillation experiments. We show that a Moessbauer neutrino experiment could
allow to distinguish different approaches and we present arguments in favor of
the 163Ho-163Dy system for such an experiment.Comment: Some small changes in section 2, results unchanged. Added referenc
Testing neutrino magnetic moment in ionization of atoms by neutrino impact
The atomic ionization processes induced by scattering of neutrinos play key
roles in the experimental searches for a neutrino magnetic moment. Current
experiments with reactor (anti)neutrinos employ germanium detectors having
energy threshold comparable to typical binding energies of atomic electrons,
which fact must be taken into account in the interpretation of the data. Our
theoretical analysis shows that the so-called stepping approximation to the
neutrino-impact ionization is well applicable for the lowest bound Coulomb
states, and it becomes exact in the semiclassical limit. Numerical evidence is
presented using the Thomas-Fermi model for the germanium atom.Comment: 5 pages, 1 figur
Orbital effects of a monochromatic plane gravitational wave with ultra-low frequency incident on a gravitationally bound two-body system
We analytically compute the long-term orbital variations of a test particle
orbiting a central body acted upon by an incident monochromatic plane
gravitational wave. We assume that the characteristic size of the perturbed
two-body system is much smaller than the wavelength of the wave. Moreover, we
also suppose that the wave's frequency is much smaller than the particle's
orbital one. We make neither a priori assumptions about the direction of the
wavevector nor on the orbital geometry of the planet. We find that, while the
semi-major axis is left unaffected, the eccentricity, the inclination, the
longitude of the ascending node, the longitude of pericenter and the mean
anomaly undergo non-vanishing long-term changes. They are not secular trends
because of the slow modulation introduced by the tidal matrix coefficients and
by the orbital elements themselves. They could be useful to indepenedently
constrain the ultra-low frequency waves which may have been indirectly detected
in the BICEP2 experiment. Our calculation holds, in general, for any
gravitationally bound two-body system whose characteristic frequency is much
larger than the frequency of the external wave. It is also valid for a generic
perturbation of tidal type with constant coefficients over timescales of the
order of the orbital period of the perturbed particle.Comment: LaTex2e, 24 pages, no figures, no tables. Changes suggested by the
referees include
Phenomenology of the Lense-Thirring effect in the Solar System
Recent years have seen increasing efforts to directly measure some aspects of
the general relativistic gravitomagnetic interaction in several astronomical
scenarios in the solar system. After briefly overviewing the concept of
gravitomagnetism from a theoretical point of view, we review the performed or
proposed attempts to detect the Lense-Thirring effect affecting the orbital
motions of natural and artificial bodies in the gravitational fields of the
Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of
the impact of several sources of systematic uncertainties of dynamical origin
to realistically elucidate the present and future perspectives in directly
measuring such an elusive relativistic effect.Comment: LaTex, 51 pages, 14 figures, 22 tables. Invited review, to appear in
Astrophysics and Space Science (ApSS). Some uncited references in the text
now correctly quoted. One reference added. A footnote adde