Medium modification of the charged current neutrino opacity and its implications

Previous work on neutrino emission from proto-neutron stars which employed full solutions of the Boltzmann equation showed that the average energies of emitted electron neutrinos and antineutrinos are closer to one another than predicted by older, more approximate work. This in turn implied that the neutrino driven wind is proton rich during its entire life, precluding $r$-process nucleosynthesis and the synthesis of Sr, Y, and Zr. This work relied on charged current neutrino interaction rates that are appropriate for a free nucleon gas. Here, it is shown in detail that the inclusion of the nucleon potential energies and collisional broadening of the response significantly alters this conclusion. Iso-vector interactions, which give rise to the nuclear symmetry energy, produce a difference between the neutron and proton single-particle energies $\Delta U=U_n-U_p$ and alter the kinematics of the charged current reactions. In neutron-rich matter, and for a given neutrino/antineutrino energy, the rate for $\nu_e+n\rightarrow e^-+p$ is enhanced while $\bar{\nu}_e+p\rightarrow n+e^+$ is suppressed because the $Q$ value for these reactions is altered by $\pm\Delta U$, respectively. In the neutrino decoupling region, collisional broadening acts to enhance both $\nu_e$ and $\bar{\nu}_e$ cross-sections and RPA corrections decrease the $\nu_e$ cross-section and increase the $\bar \nu_e$ cross-section, but mean field shifts have a larger effect. Therefore, electron neutrinos decouple at lower temperature than when the nucleons are assumed to be free and have lower average energies. The change is large enough to allow for a reasonable period of time when the neutrino driven wind is predicted to be neutron rich. It is also shown that the electron fraction in the wind is influenced by the nuclear symmetry energy.Comment: Version submitted to PRC, 10 pages, 6 figures (Additional discussion of RPA effects added

Kinetic study for hopping conduction through DNA molecules

Recent experiments indicated that disorder effect in DNA may lead to a transition of the charge transport mechanism from band resonant tunnelling to thermal activated hopping. In this letter, based on Mott's variable-range hopping theory we present a kinetic study for the charge transport properties of DNA molecules. Beyond the conventional argument in large-scale systems, our numerical study for finite-size DNA molecules reveals a number of unique features for (i) the I-V characteristics, (ii) the temperature and length dependence, and (iii) the transition from conducting to insulating behaviors.Comment: 3 pages, 3 figures, submitted to Appl. Phys. Let

Has HyperCP Observed a Light Higgs Boson?

The HyperCP collaboration has observed three events for the decay Sigma^+ -> p mu^+ mu^- which may be interpreted as a new particle of mass 214.3 MeV. However, existing data from kaon and B-meson decays severely constrain this interpretation, and it is nontrivial to construct a model consistent with all the data. In this letter we show that the ``HyperCP particle'' can be identified with the light pseudoscalar Higgs boson in the next-to-minimal supersymmetric standard model, the A_1^0. In this model there are regions of parameter space where the A_1^0 can satisfy all the existing constraints from kaon and B-meson decays and mediate Sigma^+ -> p mu^+ mu^- at a level consistent with the HyperCP observation.Comment: 7 pages, 2 figure

Thermal rectifier from deformed carbon nanohorns

We study thermal rectification in single-walled carbon nanohorns (SWNHs) by using non-equilibrium molecular dynamics (MD) method. It is found that the horns with the bigger top angles show larger asymmetric heat transport due to the larger structural gradient distribution. This kind of gradient behavior can be further adjusted by applying external strain on the SWNHs. After being carefully elongated along the axial direction, the thermal rectification in the elongated SWNHs can become more obvious than that in undeformed ones. The maximum rectification efficiency of SWNHs is much bigger than that of carbon nanotube intramolecular junctions.Comment: 3 figure

Superfluid-Insulator Transitions on the Triangular Lattice

We report on a phenomenological study of superfluid to Mott insulator transitions of bosons on the triangular lattice, focusing primarily on the interplay between Mott localization and geometrical charge frustration at 1/2-filling. A general dual vortex field theory is developed for arbitrary rational filling factors f, based on the appropriate projective symmetry group. At the simple non-frustrated density f=1/3, we uncover an example of a deconfined quantum critical point very similar to that found on the half-filled square lattice. Turning to f=1/2, the behavior is quite different. Here, we find that the low-energy action describing the Mott transition has an emergent nonabelian SU(2)\times U(1) symmetry, not present at the microscopic level. This large nonabelian symmetry is directly related to the frustration-induced quasi-degeneracy between many charge-ordered states not related by microscopic symmetries. Through this ``pseudospin'' SU(2)symmetry, the charged excitations in the insulator close to the Mott transition develop a skyrmion-like character. This leads to an understanding of the recently discovered supersolid phase of the triangular lattice XXZ model (cond-mat/0505258, cond-mat/0505257, cond-mat/0505298) as a ``partially melted'' Mott insulator. The latter picture naturally explains a number of puzzling numerical observations of the properties of this supersolid. Moreover, we predict that the nearby quantum phase transition from this supersolid to the Mott insulator is in the recently-discovered non-compact CP^1 critical universality class (PRB 70, 075104 (2004)). A description of a broad range of other Mott and supersolid states, and a diverse set of quantum critical points between them, is also provided.Comment: 24 pages, 14 figure

Analysis of the X(1576) as a tetraquark state with the QCD sum rules

In this letter, we take the point of view that the X(1576) be tetraquark state which consists of a scalar-diquark and an anti-scalar-diquark in relative $P$-wave, and calculate its mass in the framework of the QCD sum rules approach. The numerical value of the mass $m_X=(1.66\pm 0.14) GeV$ is consistent with the experimental data, there may be some tetraquark component in the vector meson X(1576).Comment: 6 pages, 1 figure, second version, typos correcte

Quantum Phase Transition in Finite-Size Lipkin-Meshkov-Glick Model

Lipkin model of arbitrary particle-number N is studied in terms of exact differential-operator representation of spin-operators from which we obtain the low-lying energy spectrum with the instanton method of quantum tunneling. Our new observation is that the well known quantum phase transition can also occur in the finite-N model only if N is an odd-number. We furthermore demonstrate a new type of quantum phase transition characterized by level-crossing which is induced by the geometric phase interference and is marvelously periodic with respect to the coupling parameter. Finally the conventional quantum phase transition is understood intuitively from the tunneling formulation in the thermodynamic limit.Comment: 4 figure

Thermal rectification in carbon nanotube intramolecular junctions: Molecular dynamics calculations

We study heat conduction in (n, 0)/(2n, 0) intramolecular junctions by using molecular dynamics method. It is found that the heat conduction is asymmetric, namely, heat transports preferably in one direction. This phenomenon is also called thermal rectification. The rectification is weakly dependent on the detailed structure of connection part, but is strongly dependent on the temperature gradient. We also study the effect of the tube radius and intramolecular junction length on the rectification. Our study shows that the tensile stress can increase rectification. The physical mechanism of the rectification is explained