arXiv subjects

Ephraim Fischbach

Publications and source records attributed to Ephraim Fischbach.

45 records · Page 3Linked to original sources

arXiv2001

A New Geometric Probability Technique for an N-dimensional Sphere and Its Applications to Physics

A new formalism is presented for analytically obtaining the probability density function, $ P_{n}(s) $, for the distance between two random points in an $ n $-dimensional sphere of radius $ R $. Our formalism allows $ P_{n}(s) $ to be calculated for a sphere having an arbitrary density distribution, and reproduces the well-known results for the case of a sphere with uniform density. The results find applications in stochastic geometry, probability distribution theory, astrophysics, nuclear physics, and elementary particle physics.

math-ph↗

arXiv1999

Searching for Extra Dimensions and New String-Inspired Forces in the Casimir Regime

The appearance of new fundamental forces and extra-dimensional modifications to gravity in extensions of the Standard Model has motivated considerable interest in testing Newtonian gravity at short distances (<10^-3 m). Presently a number of new gravity experiments are searching for non-Newtonian effects in the ranges 10^-4 m -- 10^-3 m. However, as challenging as these experiments are, formidable new obstacles await the next generation of experiments which will probe gravity at distances <10^-4 m where Casimir/van der Waals forces become dominant. Here we will review the motivation for conducting such very short distance gravity experiments, and discuss some of the new problems that may arise in future experiments. Finally, we suggest schematic designs for null experiments which would address some of these problems using the ``iso-electronic'' and ``finite-size'' effects.

hep-ph↗

arXiv1999

Constraints on Light Pseudoscalars Implied by Tests of the Gravitational Inverse-Square Law

The exchange of light pseudoscalars between fermions leads to a spin-independent potential in order g^4, where g is the Yukawa pseudoscalar-fermion coupling constant. This potential gives rise to detectable violations of both the weak equivalence principle (WEP) and the gravitational inverse-square law (ISL), even if g is quite small. We show that when previously derived WEP constraints are combined with those arisingfrom ISL tests, a direct experimental limit on the Yukawa coupling of light pseudoscalars to neutrons can be inferred for the first time (g_n^2/4pi < 1.6 \times 10^-7), along with a new (and significantly improved) limit on the coupling of light pseudoscalars to protons.

hep-ph↗

arXiv1999

New Limits on the Couplings of Light Pseudoscalars from Equivalence Experiments

The exchange of light pseudoscalar quanta between fermions leads to long-range spin-dependent forces in order g^2, where g is the pseudoscalar-fermion coupling constant. We demonstrate that laboratory bounds on the Yukawa couplings of pseudoscalars to nucleons can be significantly improved using results from recent equivalence principle experiments, which are sensitive to the spin-independent long-range forces that arise in order g^4 from two-pseudoscalar exchange.

hep-ph↗

arXiv1998

Neutrino-Exchange Interactions in 1-, 2-, and 3-Dimensions

We examine several recent calculations of the self-energy of a neutron star arising from neutrino-exchange. It is shown that the results of Abada, et al. in 1+1 dimensions have no bearing on a 3-dimensional neutron star, since the criticality parameter (Gf N)/R^2 is always much smaller than unity in 1+1 dimensions. The calculation of Kiers and Tytgat in 3-dimensions is shown to disagree with the lowest order 2-body contribution, which is known exactly. This discrepancy raises the possibility that the description of a neutron star as a continuous medium may be inappropriate when calculating higher-order many-body effects. We conclude that none of the recent calculations contradict the earlier claims that the neutrino-exchange contributions to the self-energy of a neutron star are unphysically large, when calculated in the standard model. The implication of this result, that neutrinos must have a non-zero mass, m > 0.4 eV, remains intact.

hep-ph↗

arXiv1997

Neutrino Trapping and Neutrino Mass Bounds

It has been shown recently that the exchange of virtual neutrino pairs leads to an unphysically large energy-density in neutron stars and white dwarfs, unless neutrinos have a minimum mass, m > 0.4 eV. Here we consider the possibility that the presence of trapped low-energy neutrinos can suppress the exchange of virtual neutrino pairs, thereby avoiding a large energy-density even for massless neutrinos. We show that a) there can be subvolumes in a neutron star or white dwarf where neutrino-trapping does not take place, and which can thus have an unphysically large energy density, and b) even in those volumes where trapping does occur, the resulting suppression can be too small to alter the conclusion that neutrinos must have a minimum mass.

hep-ph↗

arXiv1996

Ten Years of the Fifth Force

The suggestion in 1986 of a possible gravity-like ``fifth" fundamental force renewed interest in the question of whether new macroscopic forces are present in nature. Such forces are predicted in many theories which unify gravity with the other known forces, and their presence can be detected by searching for apparent deviations from the predictions of Newtonian gravity. We review the phenomenology behind searches for a ``fifth force", and present a summary of the existing experimental constraints.

hep-ph↗

arXiv1996

A Lower Bound on Neutrino Mass

The exchange of massless neutrinos between heavy fermions (e.g. $e,p,n$) gives rise to a long-range 2-body force. It is shown that the analogous many-body force can lead to an unphysically large energy density in white dwarfs and neutron stars. To reduce the energy density to a physically acceptable value, the neutrino must have a {\it minimum mass}, which is approximately $0.4\;eV/c^2$. Some recent questions relating to the derivation of this bound are also discussed.

hep-ph↗

arXiv1996

Long Range Forces and Neutrino Mass

We explore the limits on neutrino mass which follow from a study of the long-range forces that arise from the exchange of massless or ultra-light neutrinos. Although the 2-body neutrino-exchange force is unobservably small, the many-body force can generate a very large energy density in neutron stars and white dwarfs. We discuss the novel features of neutrino-exchange forces which lead to large many-body effects, and present the formalism that allows these effects to be calculated explicitly in the Standard Model. After considering, and excluding, several possibilities for avoiding the unphysically large contributions from the exchange of massless neutrinos, we develop a formalism to describe the exchange of massive neutrinos. It is shown that the stability of both neutrons stars and white dwarfs in the presence of many-body neutrino-exchange forces implies a lower bound, $m \gtrsim 0.4$ eV/$c^{2}$ on the mass $m$ of any neutrino.

hep-ph↗