1,668 research outputs found
Spin-lattice instability to a fractional magnetization state in the spinel HgCr2O4
Magnetic systems are fertile ground for the emergence of exotic states when
the magnetic interactions cannot be satisfied simultaneously due to the
topology of the lattice - a situation known as geometrical frustration.
Spinels, AB2O4, can realize the most highly frustrated network of
corner-sharing tetrahedra. Several novel states have been discovered in
spinels, such as composite spin clusters and novel charge-ordered states. Here
we use neutron and synchrotron X-ray scattering to characterize the fractional
magnetization state of HgCr2O4 under an external magnetic field, H. When the
field is applied in its Neel ground state, a phase transition occurs at H ~ 10
Tesla at which each tetrahedron changes from a canted Neel state to a
fractional spin state with the total spin, Stet, of S/2 and the lattice
undergoes orthorhombic to cubic symmetry change. Our results provide the
microscopic one-to-one correspondence between the spin state and the lattice
distortion
Statistics of level spacing of geometric resonances in random binary composites
We study the statistics of level spacing of geometric resonances in the
disordered binary networks. For a definite concentration within the
interval , numerical calculations indicate that the unfolded level
spacing distribution and level number variance have the
general features. It is also shown that the short-range fluctuation and
long-range spectral correlation lie between the profiles of the
Poisson ensemble and Gaussion orthogonal ensemble (GOE). At the percolation
threshold , crossover behavior of functions and is
obtained, giving the finite size scaling of mean level spacing and
mean level number , which obey the scaling laws, and .Comment: 11 pages, 7 figures,submitted to Phys. Rev.
Study of Small-Scale Anisotropy of Ultrahigh Energy Cosmic Rays Observed in Stereo by HiRes
The High Resolution Fly's Eye (HiRes) experiment is an air fluorescence
detector which, operating in stereo mode, has a typical angular resolution of
0.6 degrees and is sensitive to cosmic rays with energies above 10^18 eV. HiRes
is thus an excellent instrument for the study of the arrival directions of
ultrahigh energy cosmic rays. We present the results of a search for
anisotropies in the distribution of arrival directions on small scales (<5
degrees) and at the highest energies (>10^19 eV). The search is based on data
recorded between 1999 December and 2004 January, with a total of 271 events
above 10^19 eV. No small-scale anisotropy is found, and the strongest
clustering found in the HiRes stereo data is consistent at the 52% level with
the null hypothesis of isotropically distributed arrival directions.Comment: 4 pages, 3 figures. Matches accepted ApJL versio
Measurement of the Flux of Ultrahigh Energy Cosmic Rays from Monocular Observations by the High Resolution Fly's Eye Experiment
We have measured the cosmic ray spectrum above 10^17.2 eV using the two air
fluorescence detectors of the High Resolution Fly's Eye observatory operating
in monocular mode. We describe the detector, photo-tube and atmospheric
calibrations, as well as the analysis techniques for the two detectors. We fit
the spectrum to a model consisting of galactic and extra-galactic sources.Comment: 4 pages, 4 figures. Uses 10pt.rtx, amsmath.sty, aps.rtx, revsymb.sty,
revtex4.cl
On the Bergman representative coordinates
We study the set where the so-called Bergman representative coordinates (or
Bergman functions) form an immersion. We provide an estimate of the size of a
maximal geodesic ball with respect to the Bergman metric, contained in this
set. By concrete examples we show that these estimates are the best possible.Comment: 20 page
Quantum fluctuations in the mazer
Quantum fluctuations in the mazer are considered, arising either from the
atomic motion or from the quantized intracavity field. Analytical results, for
both the meza and the hyperbolic secant mode profile, predict for example an
attenuation of tunneling resonances due to such fluctuations. The case of a
Gaussian mode profile is studied numerically using a wave packet propagation
approach. The method automatically takes into account fluctuations in the
atomic motion and the dynamics is especially considered at or adjacent to a
tunnel resonance. We find that the system evolution is greatly sensitive to the
atom-field detuning, bringing about a discussion about the concept of
adiabaticity in this model. Further, a novel collapse-revival phenomena is
demonstrated, originating from the quantum fluctuations in the atomic motion
rather from field fluctuations as is normally the case.Comment: 15 pages, 8 figures. Replaced with final versio
Nonlocal Field Theories and their Gravity Duals
The gravity duals of nonlocal field theories in the large N limit exhibit a
novel behavior near the boundary. To explore this, we present and study the
duals of dipole theories - a particular class of nonlocal theories with
fundamental dipole fields. The nonlocal interactions are manifest in the metric
of the gravity dual and type-0 string theories make a surprising appearance. We
compare the situation to that in noncommutative SYM.Comment: 34pp LaTeX, minor corrections, reference adde
Duality and Braiding in Twisted Quantum Field Theory
We re-examine various issues surrounding the definition of twisted quantum
field theories on flat noncommutative spaces. We propose an interpretation
based on nonlocal commutative field redefinitions which clarifies previously
observed properties such as the formal equivalence of Green's functions in the
noncommutative and commutative theories, causality, and the absence of UV/IR
mixing. We use these fields to define the functional integral formulation of
twisted quantum field theory. We exploit techniques from braided tensor algebra
to argue that the twisted Fock space states of these free fields obey
conventional statistics. We support our claims with a detailed analysis of the
modifications induced in the presence of background magnetic fields, which
induces additional twists by magnetic translation operators and alters the
effective noncommutative geometry seen by the twisted quantum fields. When two
such field theories are dual to one another, we demonstrate that only our
braided physical states are covariant under the duality.Comment: 35 pages; v2: Typos correcte
Phase diagram of bismuth in the extreme quantum limit
Elemental bismuth provides a rare opportunity to explore the fate of a
three-dimensional gas of highly mobile electrons confined to their lowest
Landau level. Coulomb interaction, neglected in the band picture, is expected
to become significant in this extreme quantum limit with poorly understood
consequences. Here, we present a study of the angular-dependent Nernst effect
in bismuth, which establishes the existence of ultraquantum field scales on top
of its complex single-particle spectrum. Each time a Landau level crosses the
Fermi level, the Nernst response sharply peaks. All such peaks are resolved by
the experiment and their complex angular-dependence is in very good agreement
with the theory. Beyond the quantum limit, we resolve additional Nernst peaks
signaling a cascade of additional Landau sub-levels caused by electron
interaction
Nuclear matter to strange matter transition in holographic QCD
We construct a simple holographic QCD model to study nuclear matter to
strange matter transition. The interaction of dense medium and hadrons is taken
care of by imposing the force balancing condition for stable D4/D6/D6
configuration. By considering the intermediate and light flavor branes
interacting with baryon vertex homogeneously distributed along R^3 space and
requesting the energy minimization, we find that there is a well defined
transition density as a function of current quark mass. We also find that as
density goes up very high, intermediate (or heavy) and light quarks populate
equally as expected from the Pauli principle. In this sense, the effect of the
Pauli principle is realized as dynamics of D-branes.Comment: 13 pages, 14 figure
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