Top quark spin correlations in the Randall-Sundrum model at the CERN Large Hadron Collider

In the Randall-Sundrum model, we study top-antitop pair production and top spin correlations at the Large Hadron Collider. In addition to the Standard Model processes, there is a new contribution to the top-antitop pair production process mediated by graviton Kaluza-Klein modes in the s-channel. We calculate the density matrix for the top-antitop pair production including the new contribution. With a reasonable parameter choice in the Randall-Sundrum model, we find a sizable deviation of the top-antitop pair production cross section and the top spin correlations from those in the Standard Model. In particular, resonant productions of the graviton Kaluza-Klein modes give rise to a remarkable enhancement of such a deviation.Comment: 18 pages, 7 figures, discussion added, typos corrected, references added, version accepted by PR

Massive Hyper-Kahler Sigma Models and BPS Domain Walls

With the non-Abelian Hyper-Kahler quotient by U(M) and SU(M) gauge groups, we give the massive Hyper-Kahler sigma models that are not toric in the N=1 superfield formalism. The U(M) quotient gives N!/[M! (N-M)!] (N is a number of flavors) discrete vacua that may allow various types of domain walls, whereas the SU(M) quotient gives no discrete vacua. We derive BPS domain wall solution in the case of N=2 and M=1 in the U(M) quotient model.Comment: 16 pages, 1 figure, contribution to the Proceedings of the International Conference on "Symmetry Methods in Physics (SYM-PHYS10)" held at Yerevan, Armenia, 13-19 Aug. 200

Femtosecond laser nanostructuring of transparent materials: from bulk to fiber lasers

Progress in high power ultra-short pulse lasers has opened new frontiers in the physics of light-matter interactions and laser material processing. Recently there has been considerable interest in the application of femtosecond lasers to writing inside transparent materials and in particular to fabrication of three-dimensional microstructures

Field evolution of the magnetic structures in Er2_2Ti2_2O7_7 through the critical point

We have measured neutron diffraction patterns in a single crystal sample of the pyrochlore compound Er$_2$Ti$_2$O$_7$ in the antiferromagnetic phase (T=0.3\,K), as a function of the magnetic field, up to 6\,T, applied along the [110] direction. We determine all the characteristics of the magnetic structure throughout the quantum critical point at $H_c$=2\,T. As a main result, all Er moments align along the field at $H_c$ and their values reach a minimum. Using a four-sublattice self-consistent calculation, we show that the evolution of the magnetic structure and the value of the critical field are rather well reproduced using the same anisotropic exchange tensor as that accounting for the local paramagnetic susceptibility. In contrast, an isotropic exchange tensor does not match the moment variations through the critical point. The model also accounts semi-quantitatively for other experimental data previously measured, such as the field dependence of the heat capacity, energy of the dispersionless inelastic modes and transition temperature.Comment: 7 pages; 8 figure

Phase reduction of stochastic limit cycle oscillators

We point out that the phase reduction of stochastic limit cycle oscillators has been done incorrectly in the literature. We present a correct phase reduction method for oscillators driven by weak external white Gaussian noises. Numerical evidence demonstrates that the present phase equation properly approximates the dynamics of the original full oscillator system.Comment: 4 pages, 2 figure

Trions in a periodic potential

The group-theoretical classification of trion states is presented. It is based on considerations of products of irreducible representations of the 2D translation group. For a given BvK period N degeneracy of obtained states is N^2. Trions consist of two identical particles so the symmetrization of states with respect to particles transposition is considered. Completely antisymmetric states can be constructed by introducing antisymmetric spin functions. Two symmetry adapted bases are considered. The third possibility is postponed for the further investigations.Comment: revtex, 5 p., sub. to Physica

Influence of the Varus-Valgus Instability of the Contact of the Femora-Tibial Joint

Knee joint instability may occur in rupture of ligaments, especially of the anterior cruciate ligament (ACL) (Inouc et ai, 1987). Also in Charcot's joint, with loss of synergistic reflexes and deep sensation loss, the muscles and stretched ligaments cannot retain normal alignment and stability of the joint. This in turn results in faulty weight bearing with excessive stress upon the articular surfaces and in destruction of the joint (Katz et ai, 1961). To assess the changes in articular surface contact of the unstable knee joint, the contact pressures of the femoro-tibial joint with varus or valgus alignment were measured using a newly developed system

ZOOTAXA: Guide to the Parasites of Fishes of Canada Part V: Nematoda

Keys are provided for the identification of the nematode species known to be parasites of Canadian fishes. The nematodes are described and illustrated, with a note of the site(s) they occupy in named fish host(s) and their geographical distribution. Parasite records are given by author and date, full details of which can be found in a bibliography of over 800 references. Diagnoses and keys for 22 Families, 47 genera and 88 species of nematodes are also given, together with a glossary of terms, a host-parasite list, and indices to both nematode parasites and host

Ab initio study of the photoabsorption of 4^4He

There are some discrepancies in the low energy data on the photoabsorption cross section of $^4$He. We calculate the cross section with realistic nuclear forces and explicitly correlated Gaussian functions. Final state interactions and two- and three-body decay channels are taken into account. The cross section is evaluated in two methods: With the complex scaling method the total absorption cross section is obtained up to the rest energy of a pion, and with the microscopic $R$-matrix method both cross sections $^4$He($\gamma, p$)$^3$H and $^4$He($\gamma, n$)$^3$He are calculated below 40\,MeV. Both methods give virtually the same result. The cross section rises sharply from the $^3$H+$p$ threshold, reaching a giant resonance peak at 26--27\,MeV. Our calculation reproduces almost all the data above 30\,MeV. We stress the importance of $^3$H+$p$ and $^3$He+$n$ cluster configurations on the cross section as well as the effect of the one-pion exchange potential on the photonuclear sum rule.Comment: 15 pages, 12 figure

Boundary Scattering in Ballistic Graphene

We report magnetotransport measurements in ballistic graphene/hexagonal boron nitride mesoscopic wires where the charge carrier mean free path is comparable to wire width $W$. Magnetoresistance curves show characteristic peak structures where the peak field scales with the ratio of cyclotron radius $R_\textrm{c}$ and wire width $W$ as $W/R_\textrm{c} = 0.9 \pm 0.1$, due to diffusive boundary scattering. The obtained proportionality constant between $R_\textrm{c}$ and $W$ differs from that of a classical semiconductor 2D electron system where $W/R_\textrm{c} = 0.55$.Comment: 14 pages, 4 figure