Nonlinear Evolution of Cosmic Magnetic Fields and Cosmic Microwave Background Anisotropies

In this work we investigate the effects of the primordial magnetic fields on cosmic microwave background anisotropies (CMB). Based on cosmological magnetohydrodynamic (MHD) simulations we calculate the CMB anisotropy spectra and polarization induced by fluid fluctuations (Alfv\'en modes) generated by primordial magnetic fields. The strongest effect on the CMB spectra comes from the transition epoch from a turbulent regime to a viscous regime. The balance between magnetic and kinetic energy until the onset of the viscous regime provides a one to one relation between the comoving coherence length $L$ and the comoving magnetic field strength $B$, such as $L \sim 30 (B/10^{-9}{\rm G})^3 \rm pc$. The resulting CMB temperature and polarization anisotropies are somewhat different from the ones previously obtained by using linear perturbation theory. Our calculation gives a constraint on the magnetic field strength in the intermediate scale of CMB observations. Upper limits are set by WMAP and BOOMERANG results for comoving magnetic field strength of $B < 28 \rm nG$ with a comoving coherence length of $L > 0.7 \rm Mpc$ for the most extreme case, or $B 0.8 \rm Mpc$ for the most conservative case.Comment: accepted for publication in Phys. Rev.

Optical Aharonov-Bohm Effect on Wigner Molecules in Type-II Semiconductor Quantum Dots

We theoretically examine the magnetoluminescence from a trion and a biexciton in a type-II semiconductor quantum dot, in which holes are confined inside the quantum dot and electrons are in a ring-shaped region surrounding the quantum dot. First, we show that two electrons in the trion and biexciton are strongly correlated to each other, forming a Wigner molecule: Since the relative motion of electrons is frozen, they behave as a composite particle whose mass and charge are twice those of a single electron. As a result, the energy of the trion and biexciton oscillates as a function of magnetic field with half the period of the single-electron Aharonov-Bohm oscillation. Next, we evaluate the photoluminescence. Both the peak position and peak height change discontinuously at the transition of the many-body ground state, implying a possible observation of the Wigner molecule by the optical experiment.Comment: 10 pages, 10 figures, accepted for publication in Phys. Rev.

Winding Number in String Field Theory

Motivated by the similarity between cubic string field theory (CSFT) and the Chern-Simons theory in three dimensions, we study the possibility of interpreting N=(\pi^2/3)\int(U Q_B U^{-1})^3 as a kind of winding number in CSFT taking quantized values. In particular, we focus on the expression of N as the integration of a BRST-exact quantity, N=\int Q_B A, which vanishes identically in naive treatments. For realizing non-trivial N, we need a regularization for divergences from the zero eigenvalue of the operator K in the KBc algebra. This regularization must at same time violate the BRST-exactness of the integrand of N. By adopting the regularization of shifting K by a positive infinitesimal, we obtain the desired value N[(U_tv)^{\pm 1}]=\mp 1 for U_tv corresponding to the tachyon vacuum. However, we find that N[(U_tv)^{\pm 2}] differs from \mp 2, the value expected from the additive law of N. This result may be understood from the fact that \Psi=U Q_B U^{-1} with U=(U_tv)^{\pm 2} does not satisfy the CSFT EOM in the strong sense and hence is not truly a pure-gauge in our regularization.Comment: 20 pages, no figures; v2: references added, minor change

Path-Integral Formulation of Casimir Effects in Supersymmetric Quantum Electrodynamics

The Casimir effect is an interesting phenomenon in the sense that it provides us with one of the primitive means of extracting the energy out of the vacuum. Since the original work of Casimir a number of works have appeared in extending the result to the case of more general topological and dynamical configurations of the boundary condition and to the circumstances at finite temperature and gravity. In the studies of the Casimir effects it is common to assume the free electromagnetic field in the bounded region. It may be interesting to extend our arguments for fields other than the electromagnetic field. The Casimir effect due to the free fermionic fields has been investigated by several authors and has been found to result in an attractive force under the suitable physical boundary conditions.Comment: 12 pages, 6 figures, REVTe

Torsion-induced persistent current in a twisted quantum ring

We describe the effects of geometric torsion on the coherent motion of electrons along a thin twisted quantum ring. The geometric torsion inherent in the quantum ring triggers a quantum phase shift in the electrons' eigenstates, thereby resulting in a torsion-induced persistent current that flows along the twisted quantum ring. The physical conditions required for detecting the current flow are discussed.Comment: 9 pages, 3 figure

Heat capacity uncovers physics of a frustrated spin tube

We report on refined experimental results concerning the low-temperature specific heat of the frustrated spin tube material [(CuCl2tachH)3Cl]Cl2. This substance turns out to be an unusually perfect spin tube system which allows to study the physics of quasi-one dimensional antiferromagnetic structures in rather general terms. An analysis of the specific heat data demonstrates that at low enough temperatures the system exhibits a Tomonaga-Luttinger liquid behavior corresponding to an effective spin-3/2 antiferromagnetic Heisenberg chain with short-range exchange interactions. On the other hand, at somewhat elevated temperatures the composite spin structure of the chain is revealed through a Schottky-type peak in the specific heat located around 2 K. We argue that the dominating contribution to the peak originates from gapped magnon-type excitations related to the internal degrees of freedom of the rung spins.Comment: 4+ pages, 6 figure

The Infrared Cloud Monitor for the MAGNUM Robotic Telescope at Haleakala

We present the most successful infrared cloud monitor for a robotic telescope. This system was originally developed for the MAGNUM 2-m telescope, which has been achieving unmanned and automated monitoring observation of active galactic nuclei at Haleakala on the Hawaiian island of Maui since 2001. Using a thermal imager and two aspherical mirrors, it at once sees almost the whole sky at a wavelength of $\lambda\sim 10\mu{\rm m}$. Its outdoor part is weather-proof and is totally maintenance-free. The images obtained every one or two minutes are analysed immediately into several ranks of weather condition, from which our automated observing system not only decides to open or close the dome, but also selects what types of observations should be done. The whole-sky data accumulated over four years show that 50$-$60 % of all nights are photometric, and about 75 % are observable with respect to cloud condition at Haleakala. Many copies of this system are now used all over the world such as Mauna Kea in Hawaii, Atacama in Chile, and Okayama and Kiso in Japan.Comment: 18 pages, 15 figures, 7 tables, accepted for publication in PAS

Anomalous phase shift in a twisted quantum loop

Coherent motion of electrons in a twisted quantum ring is considered to explore the effect of torsion inherent to the ring. Internal torsion of the ring composed of helical atomic configuration yields a non-trivial quantum phase shift in the electrons' eigenstates. This torsion-induced phase shift causes novel kinds of persistent current flow and an Aharonov-Bohm like conductance oscillation. The two phenomena can occur even when no magnetic flux penetrates inside the twisted ring, thus being in complete contrast with the counterparts observed in untwisted rings.Comment: 13 paes, 5 figure

Kinetic Equations for Baryogenesis via Sterile Neutrino Oscillation

We investigate baryogenesis in the $\nu$MSM (neutrino Minimal Standard Model), which is the MSM extended by three right-handed neutrinos with masses below the electroweak scale. The baryon asymmetry of the universe can be generated by the mechanism via flavor oscillation of right-handed (sterile) neutrinos which are responsible to masses of active neutrinos confirmed by various experiments. We present the kinetic equations for the matrix of densities of leptons which describe the generation of asymmetries. Especially, the momentum dependence of the matrix of densities is taken into account. By solving these equations numerically, it is found that the momentum distribution is significantly distorted from the equilibrium one, since the production for the modes with lower momenta $k \ll T$ ($T$ is the temperature of the universe) is enhanced, while suppressed for higher modes. As a result, the most important mode for the yields of sterile neutrinos as well as the baryon asymmetry is $k \simeq 2 T$, which is smaller than inferred from the thermal average. The comparison with the previous works is also discussed.Comment: 22 pages, 19 figure