Effective Potential Study of the Chiral Phase Transition in a QCD-like Theory

We construct the effective potential for a QCD-like theory using the auxiliary field method. The chiral phase transition exhibited by the model at finite temperature and the quark chemical potential is studied from the viewpoint of the shape change of the potential near the critical point. We further generalize the effective potential so as to have quark number and scalar quark densities as independent variables near the tri-critical point.Comment: 17 pages, 9 figures, using PTPTeX.cl

Re/Os constraint on the time-variability of the fine-structure constant

We argue that the accuracy by which the isochron parameters of the decay $^{187}{\rm Re}\to ^{187}{\rm Os}$ are determined by dating iron meteorites may not directly constrain the possible time-dependence of the decay rate and hence of the fine-structure constant $\alpha$. From this point of view, some of the attempts to analyze the Oklo constraint and the results of the QSO absorption lines are re-examined.Comment: 7 pages, 3 figures; v2, revised top sentence on p.

Mixed magnetic phases in (Ga,Mn)As epilayers

Two different ferromagnetic-paramagnetic transitions are detected in (Ga,Mn)As/GaAs(001) epilayers from ac susceptibility measurements: transition at a higher temperature results from (Ga,Mn)As cluster phases with [110] uniaxial anisotropy and that at a lower temperature is associated with a ferromagnetic (Ga,Mn)As matrix with cubic anisotropy. A change in the magnetic easy axis from [100] to [110] with increasing temperature can be explained by the reduced contribution of cubic anisotropy to the magnetic properties above the transition temperature of the (Ga,Mn)As matrix

Hysteretic current-voltage characteristics and resistance switching at a rectifying Ti/Pr0.7_{0.7}Ca0.3_{0.3}MnO3_{3} interface

We have characterized the vertical transport properties of epitaxial layered structures composed of Pr$_{0.7}$Ca$_{0.3}$MnO$_{3}$ (PCMO) sandwiched between SrRuO$_{3}$ (SRO) bottom electrode and several kinds of top electrodes such as SRO, Pt, Au, Ag, and Ti. Among the layered structures, Ti/PCMO/SRO is distinct due to a rectifying current-voltage ($I$--$V$) characteristic with a large hysteresis. Corresponding to the hysteresis of the $I$--$V$ characteristics, the contact resistance of the Ti/PCMO interface reversibly switches between two stable states by applying pulsed voltage stress. We propose a model for the resistance switching at the Ti/PCMO interface, in which the width and/or height of a Schottky-like barrier are altered by trapped charge carriers in the interface states.Comment: 3 pages, 4 figures, Appl. Phys. Lett., in pres

BRIDGE: A Direct-tree Hybrid N-body Algorithm for Fully Self-consistent Simulations of Star Clusters and their Parent Galaxies

We developed a new direct-tree hybrid N-body algorithm for fully self-consistent N-body simulations of star clusters in their parent galaxies. In such simulations, star clusters need high accuracy, while galaxies need a fast scheme because of the large number of the particles required to model it. In our new algorithm, the internal motion of the star cluster is calculated accurately using the direct Hermite scheme with individual timesteps and all other motions are calculated using the tree code with second-order leapfrog integrator. The direct and tree schemes are combined using an extension of the mixed variable symplectic (MVS) scheme. Thus, the Hamiltonian corresponding to everything other than the internal motion of the star cluster is integrated with the leapfrog, which is symplectic. Using this algorithm, we performed fully self-consistent N-body simulations of star clusters in their parent galaxy. The internal and orbital evolutions of the star cluster agreed well with those obtained using the direct scheme. We also performed fully self-consistent N-body simulation for large-N models ($N=2\times 10^6$). In this case, the calculation speed was seven times faster than what would be if the direct scheme was used.Comment: 12 pages, 13 figures, Accepted for PAS

Survival Rates of Planets in Open Clusters: the Pleiades, Hyades, and Praesepe clusters

In clustered environments, stellar encounters can liberate planets from their host stars via close encounters. Although the detection probability of planets suggests that the planet population in open clusters resembles that in the field, only a few dozen planet-hosting stars have been discovered in open clusters. We explore the survival rates of planets against stellar encounters in open clusters similar to the Pleiades, Hyades, and Praesepe and embedded clusters. We performed a series of N-body simulations of high-density and low-density open clusters, open clusters that grow via mergers of subclusters, and embedded clusters. We semi-analytically calculated the survival rate of planets in star clusters up to 1Gyr using relative velocities, masses, and impact parameters of intruding stars. Less than 1.5% of close-in planets within 1 AU and at most 7% of planets with 1-10 AU are ejected by stellar encounters in clustered environments after the dynamical evolution of star clusters. If a planet population from 0.01-100 AU in an open cluster initially follows the probability distribution function of exoplanets with semi-major axis ($a_p$) between 0.03-3 AU in the field discovered by RV surveys, the PDF of surviving planets beyond ~10 AU in open clusters can be slightly modified to $\propto a_p^{-0.76}$. The production rate of free-floating planets (FFPs) per star is 0.0096-0.18, where we have assumed that all the stars initially have one giant planet with a mass of 1--13 MJ in a circular orbit. The expected frequency of FFPs is compatible with the upper limit on that of FFPs indicated by recent microlensing surveys. Our survival rates of planets in open clusters suggest that planets within 10 AU around FGKM-type stars are rich in relatively-young (<~10-100 Myr for open clusters and ~1-10 Myr for embedded clusters), less massive open clusters, which are promising targets for planet searches.Comment: 23 pages, 15 figures, A&A accepte

An Assessment of the Responsibility for the Increase in the CO2 Concentration and Inter-generational Carbon Accounts

Evidence is accumulating that it will be necessary to reduce global carbon dioxide emissions and other anthropogenic sources of greenhouse gases. Most of the proposed measures appear to be insufficient in causing a sufficient reduction by themselves and in very few cases a stabilization of global carbon dioxide emissions. Thus, it would be prudent in the future to expand the range of policy options that can help reduce the emissions. Furthermore, most of the proposed reduction measures such as carbon taxes, tradable permits, national or per capita emission quotas are all associated with numerous and complex global tradeoffs and important equity issues. This paper represents an attempt to develop a yardstick for establishing equitable criteria for greenhouse gas reduction strategies. The timeliness and policy relevance of such research is illustrated by ongoing discussions about international and intergenerational inequalities that can be expected to result from climate change and possibly also from many of the proposed response strategies. For example, if such policies were only based on current per capita emission levels, they would place an unequal burden on the developing countries and their future populations. Industrialization has brought hitherto unknown wealth to the developed parts of the world but also high carbon dioxide emission levels since the 19th century. Much of these emissions from last century still remain in the atmosphere due to long residence time for carbon dioxide. Thus, a significant share of current atmospheric concentration of anthropogenic carbon dioxide is due to historical emissions above and beyond the factor of ten difference in current per capita emissions between developed and developing countries. Therefore, future generations especially in the developing countries will have to bear a potential burden of our current and inherited emissions. This is certainly not equitable for humanity as a whole. A possible criterion of equity would be that every human being, past or "future", is allowed the same emission quota on annual basis. This could provide for intergenerational and interpersonal equity throughout the world, but would also imply that some of the developed regions would have an excess of historical carbon emissions or a "deficit" of future annual per capita quotas. Consider further that there exist an ultimate carrying capacity limit to the total (hypothetical cumulative) gigatons of carbon that can be "deposited" in the atmosphere as a global "resource" or "carbon credit" available to the humanity. How large would this resource have to be in order to fulfill the suggested intergenerational and interpersonal equity criterion? Fujii's analysis shows that the hypothetical resource would have to be in excess of 1,000 gigatons, probably way too much from the perspective of potential global warming. This analysis reveals significant regional and intergenerational disparities in historical contributions to current atmospheric carbon dioxide concentration and to cumulative emissions. In terms of cumulative person-years, the developed countries have contributed the lion's share to current concentrations, while the majority of "future" person-years will he in the now developing countries that would he forced to offset the large historical emission "deficit" of past generations in the industrialized countries. These disparities in per capita annual emissions ought to be considered in negotiations on greenhouse gas reductions, in the corresponding policies and any international carbon accounting system. Even if it turns out that equity does not necessarily imply interpersonal and intergenerational equality of emission permits on annual basis, the analysis in this paper can provide a yardstick for the assessment of other equity criteria that would extend beyond the current generation and current emissions

Lefschetz thimble structure in one-dimensional lattice Thirring model at finite density

We investigate Lefschetz thimble structure of the complexified path-integration in the one-dimensional lattice massive Thirring model with finite chemical potential. The lattice model is formulated with staggered fermions and a compact auxiliary vector boson (a link field), and the whole set of the critical points (the complex saddle points) are sorted out, where each critical point turns out to be in a one-to-one correspondence with a singular point of the effective action (or a zero point of the fermion determinant). For a subset of critical point solutions in the uniform-field subspace, we examine the upward and downward cycles and the Stokes phenomenon with varying the chemical potential, and we identify the intersection numbers to determine the thimbles contributing to the path-integration of the partition function. We show that the original integration path becomes equivalent to a single Lefschetz thimble at small and large chemical potentials, while in the crossover region multi thimbles must contribute to the path integration. Finally, reducing the model to a uniform field space, we study the relative importance of multiple thimble contributions and their behavior toward continuum and low-temperature limits quantitatively, and see how the rapid crossover behavior is recovered by adding the multi thimble contributions at low temperatures. Those findings will be useful for performing Monte-Carlo simulations on the Lefschetz thimbles.Comment: 32 pages, 14 figures (typo etc. corrected

Super-soft symmetry energy encountering non-Newtonian gravity in neutron stars

Considering the non-Newtonian gravity proposed in the grand unification theories, we show that the stability and observed global properties of neutron stars can not rule out the super-soft nuclear symmetry energies at supra-saturation densities. The degree of possible violation of the Inverse-Square-Law of gravity in neutron stars is estimated using an Equation of State (EOS) of neutron-rich nuclear matter consistent with the available terrestrial laboratory data.Comment: Version accepted by Physical Review Letter