Mechanical Translation

Contains reports on two research projects.National Science Foundatio

Mechanical Translation

Contains research objectives and reports one two research projects.National Science Foundatio

Large Scale Inhomogeneities from the QCD Phase Transition

We examine the first-order cosmological QCD phase transition for a large class of parameter values, previously considered unlikely. We find that the hadron bubbles can nucleate at very large distance scales, they can grow as detonations as well as deflagrations, and that the phase transition may be completed without reheating to the critical temperature. For a subset of the parameter values studied, the inhomogeneities generated at the QCD phase transition might have a noticeable effect on nucleosynthesis.Comment: 15 LaTeX pages + 6 PostScript figures appended at the end of the file, HU-TFT-94-1

Thermal origin of neutron star magnetic fields

It is proposed that magnetic field arises naturally in neutron stars as a consequence of thermal effects occurring in their outer crusts. The heat flux through the crust, which is carried mainly by degenerate electrons, can give rise to a possible thermoelectric instability in the solid crust which causes horizontal magnetic field components to grow exponentially with time. However, in order for the thermally driven growth to exceed ohmic decay, either the electron collision time must exceed existing estimates by a factor ∼ 3 or the surface layers comprise helium. A second instability is possible if the liquid phase that lies above the solid crust also contains a horizontal magnetic field. The heat flux will drive circulation which should amplify the field strength provided that there is a seed field in excess of ∼ 10^8 G. If either of these two instabilities develops the field will quickly grow to a strength of ∼ 10^(12) G, where the instabilities become non-linear. Further growth will saturate when either the magnetic stress exceeds the lattice yield stress or the temperature perturbations become non-linear, both of which occur at a subsurface field strength of ∼ 10^(14) G; the corresponding surface field strength is ∼ 10^(12) G. Further evolution of the magnetic field should lead to long-range order and yield neutron star magnetic dipole moments ∼ 10^(30) G cm^3, comparable with those observed. Newly-formed neutron stars should be able to develop their dipole moments in a hundred thousand years and maintain them for as long as heat flows through the crust. Thereafter, the dipole moment should decay in several million years, as observed in the case of most radio pulsars. Neutron stars that are formed spinning rapidly, like that in the Crab Nebula, should be able to grow magnetic fields far more rapidly since their rotational energy can also be tapped to drive thermoelectric currents. The interiors of neutron stars in binary systems may be heated by the energy released by accreting matter. The resulting heat flux may cause the production of magnetic fields in these objects. Binary pulsars, with their unusually low and persistent fields, have probably passed through this phase

A New Sub-Period-Minimum Cataclysmic Variable With Partial Hydrogen Depletion And Evidence Of Spiral Disk Structure

We present time-resolved spectroscopy and photometry of CSS 120422:111127+571239 (=SBS 1108+574), a recently discovered SU UMa-type dwarf nova whose 55 minute orbital period is well below the cataclysmic variable (CV) period minimum of similar to 78 minutes. In contrast with most other known CVs, its spectrum features He I emission of comparable strength to the Balmer lines, implying a hydrogen abundance less than 0.1 of long-period CVs-but still at least 10 times higher than that in AM CVn stars. Together, the short orbital period and remarkable helium-to-hydrogen ratio suggest that mass transfer in CSS 120422 began near the end of the donor star's main-sequence lifetime, meaning that this CV is a strong candidate progenitor of an AM CVn system as described by Podsiadlowski et al. Moreover, a Doppler tomogram of the Ha line reveals two distinct regions of enhanced emission. While one is the result of the stream-disk impact, the other is probably attributable to spiral disk structure generated when material in the outer disk achieves a 2:1 orbital resonance with respect to the donor.NSF AST-1211196, AST-9987045Department of Physics at the University of Notre DameNSF Telescope System Instrumentation Program (TSIP)Ohio Board of RegentsOhio State University Office of ResearchAstronom

ERTS and aircraft multispectral scanner digital data users manual

There are no author-identified significant results in this report

Is the Yb2Ti2O7 pyrochlore a quantum spin ice?

We use numerical linked cluster (NLC) expansions to compute the specific heat, C(T), and entropy, S(T), of a quantum spin ice model of Yb2Ti2O7 using anisotropic exchange interactions recently determined from inelastic neutron scattering measurements and find good agreement with experimental calorimetric data. In the perturbative weak quantum regime, this model has a ferrimagnetic ordered ground state, with two peaks in C(T): a Schottky anomaly signalling the paramagnetic to spin ice crossover followed at lower temperature by a sharp peak accompanying a first order phase transition to the ferrimagnetic state. We suggest that the two C(T) features observed in Yb2Ti2O7 are associated with the same physics. Spin excitations in this regime consist of weakly confined spinon-antispinon pairs. We suggest that conventional ground state with exotic quantum dynamics will prove a prevalent characteristic of many real quantum spin ice materials.Comment: 8 pages (two-column), 9 figure

Finite temperature effects on cosmological baryon diffusion and inhomogeneous Big-Bang nucleosynthesis

We have studied finite temperature corrections to the baryon transport cross sections and diffusion coefficients. These corrections are based upon the recently computed renormalized electron mass and the modified state density due to the background thermal bath in the early universe. It is found that the optimum nucleosynthesis yields computed using our diffusion coefficients shift to longer distance scales by a factor of about 3. We also find that the minimum value of $^4 He$ abundance decreases by $\Delta Y_p \simeq 0.01$ while $D$ and $^7 Li$ increase. Effects of these results on constraints from primordial nucleosynthesis are discussed. In particular, we find that a large baryonic contribution to the closure density (\Omega_b h_{50}^{2} \lsim 0.4) may be allowed in inhomogeneous models corrected for finite temperature.Comment: 7 pages, 6 figures, submitted to Phys. Rev.