Observer dependence of the quasi-local energy and momentum in Schwarzschild space-time

The observer dependence of the quasi-local energy (QLE) and momentum in the Schwarzschild geometry is illustrated. Using the Brown-York prescription, the QLE for families of non-geodesic and geodesic observers penetrating the event horizon is obtained. An explicit shell-building process is presented and the binding energy is computed in terms of the QLE measured by a static observer field at a radius outside the horizon radius. The QLE for a radially geodesic observer field freely-falling from infinity is shown to vanish. Finally, a simple relation for the dynamics of the quasi-local momentum density for a geodesic observer field is noted.Comment: 7 pages, 3 figures; accepted for publication in Gen. Rel. Gra

Cepheid Calibration of the Peak Brightness of SNe Ia. X. SN 1991T in NGC 4527

Repeated imaging observations have been made of NGC 4527 with the Hubble Space Telescope between April and June 1999, over an interval of 69 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F814W band. The galaxy hosted the type Ia supernova SN1991T, which showed relatively unusual behavior by having both an abnormal spectrum near light maximum, and a slower declining light curve than the proto-typical Branch normal SNe Ia. A total of 86 variables that are putative Cepheids have been found, with periods ranging from 7.4 days to over 70 days. From photometry with the DoPHOT program, the de-reddened distance modulus is determined to be (m-M)_0 = 30.67 +/- 0.12 (internal uncertainty) using a subset of the Cepheid data whose reddening and error parameters are secure. A parallel analysis of the Cepheids using photometry with ROMAFOT yields (m -M)_0 =30.82 +/- 0.11. The final adopted modulus is (m -M)_0 =30.74 +/- 0.12 +/- 0.12 (d=14.1 +/- 0.8 +/- 0.8 Mpc). The photometric data for SN1991T are used in combination with the Cepheid distance to NGC 4527 to obtain the absolute magnitude for this supernova of M_V^0(max) = -19.85 +/- 0.29. The relatively large uncertainty is a result of the range in estimates of the reddening to the supernova. Thus SN1991T is seen to be only moderately brighter (by ~ 0.3 mag) than the mean for spectroscopically normal supernovae, although magnitude differences of up to 0.6 mag cannot be ruled out.Comment: 46 pages, LATEX using aaspp4.sty, including 9 embedded tables, 19 figures (gif and jpg files), a full-resolution version (ps files) is available at http://www.astro.unibas.ch/forschung/ll/cepheid.shtml, accepted for publication in the Astrophysical Journa

Brown-York Energy and Radial Geodesics

We compare the Brown-York (BY) and the standard Misner-Sharp (MS) quasilocal energies for round spheres in spherically symmetric space-times from the point of view of radial geodesics. In particular, we show that the relation between the BY and MS energies is precisely analogous to that between the (relativistic) energy E of a geodesic and the effective (Newtonian) energy E_{eff} appearing in the geodesic equation, thus shedding some light on the relation between the two. Moreover, for Schwarzschild-like metrics we establish a general relationship between the BY energy and the geodesic effective potential which explains and generalises the recently observed connection between negative BY energy and the repulsive behaviour of geodesics in the Reissner-Nordstrom metric. We also comment on the extension of this connection between geodesics and the quasilocal BY energy to regions inside a horizon.Comment: v3: 7 pages, shortened and revised version to appear in CQ

Familon Model of Dark Matter

If the next fundamental level of matter occurs (preons) then dark matter must consist of familons containing a "hot" component from massless particles and a "cold" component from massive particles. During evolution of the Universe this dark matter was undergone to late-time relativistic phase transitions temperatures of which were different. Fluctuations created by these phase transitions have had a fractal character. In the result the structurization of dark matter (and therefore the baryon subsystem) has taken place and in the Universe some characteristic scales which have printed this phenomenon arise naturally. Familons are collective excitations of nonperturbative preon condensates which could be produced during more early relativistic phase transition. For structurization of dark matter (and baryon component) three generations of particles are necessary. The first generation of particles has produced the observed baryon world. The second and third generations have produced dark matter from particles which have appeared when symmetry among generations was spontaneously broken.Comment: 12 page

The Structure of Structure Formation Theories

We study the general structure of models for structure formation, with applications to the reverse engineering of the model from observations. Through a careful accounting of the degrees of freedom in covariant gravitational instability theory, we show that the evolution of structure is completely specified by the stress history of the dark sector. The study of smooth, entropic, sonic, scalar anisotropic, vector anisotropic, and tensor anisotropic stresses reveals the origin, robustness, and uniqueness of specific model phenomenology. We construct useful and illustrative analytic solutions that cover cases with multiple species of differing equations of state relevant to the current generation of models, especially those with effectively smooth components. We present a simple case study of models with phenomenologies similar to that of a LambdaCDM model to highlight reverse-engineering issues. A critical-density universe dominated by a single type of dark matter with the appropriate stress history can mimic a LambdaCDM model exactly.Comment: 31 pages, 18 figures, RevTeX, submitted to Phys. Rev.

A Mechanism for Ordinary-Sterile Neutrino Mixing

Efficient oscillations between ordinary (active) and sterile neutrinos can occur only if Dirac and Majorana mass terms exist which are both small and comparable. It is shown that this can occur naturally in a class of string models, in which higher-dimensional operators in the superpotential lead to an intermediate scale expectation value for a scalar field and to suppressed Dirac and Majorana fermion masses.Comment: 12 page

Standard Model Contributions to the Neutrino Index of Refraction in the Early Universe

With the standard electroweak interactions, the lowest-order coherent forward scattering amplitudes of neutrinos in a CP symmetric medium (such as the early universe) are zero, and the index of refraction of a propagating neutrino can only arise from the expansion of gauge boson propagators, from radiative corrections, and from new physics interactions. Motivated by nucleosynthesis constraints on a possible sterile neutrino (suggested by the solar neutrino deficit and a possible $17\ keV$ neutrino), we calculate the standard model contributions to the neutrino index of refraction in the early universe, focusing on the period when the temperature was of the order of a few $MeV$. We find sizable radiative corrections to the tree level result obtained by the expansion of the gauge boson propagator. For $\nu_e+e(\bar{e})\to \nu_e+e(\bar{e})$ the leading log correction is about $+10\%$, while for $\nu_e+\nu_e(\bar{\nu}_e)\to \nu_e+\nu_e(\bar{\nu}_e)$ the correction is about $+20\%$. Depending on the family mixing (if any), effects from different family scattering can be dominated by radiative corrections. The result for $\nu+\gamma\to\nu+\gamma$ is zero at one-loop level, even if neutrinos are massive. The cancellation of infrared divergence in a coherent process is also discussed.Comment: 46pp, 13 figures (not included), UPR-0495

Radiative Seesaw Mechanism at Weak Scale

We investigate an alternative seesaw mechanism for neutrino mass generation. Neutrino mass is generated at loop level but the basic concept of usual seesaw mechanism is kept. One simple model is constructed to show how this mechanism is realized. The applications of this seesaw mechanism at weak scale to cosmology and neutrino physics are discussed.Comment: 12 Pages, latex, no figure

Type Ia Supernovae and Cosmology

I discuss the use of Type Ia supernovae (SNe Ia) for cosmological distance determinations. Low-redshift SNe Ia (z < 0.1) demonstrate that the Hubble expansion is linear with H_0 = 72 +/- 8 km/s/Mpc, and that the properties of dust in other galaxies are generally similar to those of dust in the Milky Way. The measured luminosity distances of SNe Ia as a function of redshift have shown that the expansion of the Universe is currently accelerating, probably due to the presence of repulsive dark energy such as Einstein's cosmological constant (Lambda). From about 200 SNe Ia, we find that Omega_Lambda - 1.4 Omega_M = 0.35 +/- 0.14. Combining our data with other results, we find a best fit for Omega_M and Omega_Lambda of 0.28 and 0.72, respectively. A number of possible systematic effects (dust, supernova evolution) thus far do not seem to eliminate the need for Omega_Lambda > 0. Recently, analyses of SNe Ia at z = 1.0-1.7 provide further support for current acceleration, and give tentative evidence for an early epoch of deceleration. The dynamical age of the Universe is estimated to be 13.1 +/- 1.5 Gyr. According to the most recent data sets, the SN Ia rate at z > 1 is several times greater than that at low redshifts, presumably because of higher star formation rates long ago. Moreover, the typical delay time from progenitor star formation to SNIa explosion appears to be substantial, ~3 Gyr. Current projects include the measurement of a few hundred SNe Ia at z = 0.2-0.8 to more accurately determine the equation-of-state parameter of the dark energy, w = P/(\rho c^2), whose value is now constrained by SNe Ia to be in the range -1.48 < w < -0.72 at 95% confidence.Comment: 39 pages, 17 figures, to be published in "White Dwarfs: Probes of Galactic Structure and Cosmology" ed. E. M. Sion, H. L. Shipman, and S. Vennes (Kluwer: Dordrecht). Part of the Astrophysics and Space Science Library Serie

Evolution of a Kerr-Newman black hole in a dark energy universe

This paper deals with the study of the accretion of dark energy with equation of state $p=w\rho$ onto Kerr-Newman black holes. We have obtained that when $w>-1$ the mass and specific angular momentum increase, and that whereas the specific angular momentum increases up to a given plateau, the mass grows up unboundedly. On the regime where the dominant energy condition is violated our model predicts a steady decreasing of mass and angular momentum of black holes as phantom energy is being accreted. Masses and and angular momenta of all black holes tend to zero when one approaches the big rip. The results that cosmic censorship is violated and that the black hole size increases beyond the universe size itself are discussed in terms of considering the used models as approximations to a more general descriptions where the metric is time-dependent.Comment: 11 figures added. Some explanations extended. E-mails updated. References updated. Conclusions unchanged. Accepted in Gravitation & Cosmolog