Showing papers in "Physical Review in 2009"

Jet tomography of high-energy nucleus-nucleus collisions at next-to-leading order

Abstract: We demonstrate that jet observables are highly sensitive to the characteristics of the vacuum and the in-medium QCD parton showers and propose techniques that exploit this sensitivity to constrain the mechanism of quark and gluon energy loss in strongly-interacting plasmas. As a first example, we calculate the inclusive jet cross section in high-energy nucleus-nucleus collisions to {Omicron}({alpha}{sub s}{sup 3}). Theoretical predictions for the medium-induced jet broadening and the suppression of the jet production rate due to cold and hot nuclear matter effects in Au+Au and Cu+Cu reactions at RHIC are presented.

Deterministic entanglement purification and complete nonlocal Bell-state analysis with hyperentanglement

Abstract: Entanglement purification is a very important element for long-distance quantum communication. Different from all the existing entanglement purification protocols (EPPs) in which two parties can only obtain some quantum systems in a mixed entangled state with a higher fidelity probabilistically by consuming quantum resources exponentially, here we present a deterministic EPP with hyperentanglement. Using this protocl, the two parties can, in principle, obtain deterministically maximally entangled pure states in polarization without destroying any less-entangled photon pair, which will improve the efficiency of long-distance quantum communication exponentially. Meanwhile, it will be shown that this EPP can be used to complete nonlocal Bell-state analysis perfectly. We also discuss this EPP in a practical transmission.

Effective magnetic moment of magnetic multicore nanoparticles

Abstract: We carry out Monte Carlo simulations to study the effective magnetic moment mu(eff) in the low-field region of magnetic multicore nanoparticles. Transmission electron microscopy and scanning electron microscopy images show that these particles contain a number of magnetic nanocrystals (MNCs) randomly packed in a single cluster of total volume V(tot). We illustrate how the initial magnetic susceptibility chi(0) of magnetic multicore nanoparticles can be straightforward derived from mu(eff) computed at zero magnetic field. We observe that dipolar interactions between MNCs and polydispersity of the MNCs contribute to increase and to decrease mu(eff)/V(tot), respectively, while magnetic anisotropy of the MNCs does not show any effect. In all three cases, mu(eff)/V(tot) can be described by a linear relation to (mu B/k(B)T)(2) that we analytically derived for low applied fields.

Crystal structure of highly concentrated, ionic microgel suspensions studied by neutron scattering

Abstract: We present a neutron-scattering investigation of the crystal structure formed by $p\text{H}$-sensitive poly(2-vinylpyridine) microgel particles with $5\text{ }\text{wt}\text{ }%$ of cross-linker. We focus on highly swollen particles and explore concentrations ranging from below close packing to well above close packing, where the particles are forced to shrink and/or interpenetrate. The crystal structure is found to be random hexagonal close packed, similar to the structure typically found in hard-sphere systems.

Hidden MeV-scale Dark Matter in Neutrino Detectors

Abstract: The possibility of direct detection of light fermionic dark matter in neutrino detectors is explored from a model-independent standpoint. We consider all operators of dimension six or lower which can contribute to the interaction fp {yields} e{sup +}n, where f is a dark Majorana or Dirac fermion. Constraints on these operators are then obtained from the f lifetime and its decays which produce visible {gamma} rays or electrons. We find one operator which would allow fp {yields} e{sup +}n at interesting rates in neutrino detectors, as long as m{sub f} {approx}< m{sub {pi}}. The existing constraints on light dark matter from relic density arguments, supernova cooling rates, and big-bang nucleosynthesis are then reviewed. We calculate the cross section for fp {yields} e{sup +}n in neutrino detectors implied by this operator, and find that Super-Kamiokande can probe the new physics scale {Lambda} for this interaction up to O(100 TeV).

Uncharacteristic phase separation trends with ionic size in Cobaltites

Abstract: Using elastic neutron scattering on single crystals of ${\\text{La}}_{1\\ensuremath{-}x}{A}_{x}{\\text{CoO}}_{3}$ ($A={\\text{Ca}}^{2+}$, ${\\text{Sr}}^{2+}$, and ${\\text{Ba}}^{2+}$), we found the development of magnetic superstructures below the global magnetic transition to be strongly dependent on the size of the $A$-site dopant, $⟨{r}_{A}⟩$, in an unusual way. Upon reducing the $⟨{r}_{A}⟩$ (i.e., as with Ca doping), only a commensurate ferromagnetic cluster phase is evident. On expanding the $⟨{r}_{A}⟩$, the tendency toward coexistence of competing ferromagnetic and antiferromagnetic orders increases giving rise to an inhomogeneous ground state. The antiferromagnetic ordered state, initially incommensurate, continuously strengthens and becomes commensurate with long-range order and a characteristic cubic wave vector of ${\\stackrel{P\\vec}{Q}}_{c}=(0.25,0.25,0.25)$ with $x$. The two competing order parameters become comparable in magnitude indicative of the phase-separated nature of the cobalt perovskite system.