22,298 research outputs found
Spin-3/2 Fermions in Twistor Formalism
Consistency conditions for the local existence of massless spin 3/2 fields
has been explored that the field equations for massless helicity 3/2 are
consistent iff the space-time is Ricci-flat and that in Minkowski space-time
the space of conserved charges for the fields is its twistor space itself.
After considering the twistorial methods to study such massless helicity 3/2
fields, we derive in flat space-time that the charges of spin-3/2 fields
defined topologically by the first Chern number of their spin-lowered self-dual
Maxwell fields, are given by their twistor space, and in curved space-time that
the (anti-)self-duality of the space-time is the necessary condition. Since in
N=1 supergravity torsions are the essential ingredients, we generalize our
space-time to that with torsion (Einstein-Cartan theory) and have investigated
the consistency of existence of spin 3/2 fields in it. A simple solution is
found that the space-time has to be conformally (anti-)self-dual, left-(or
right-)torsion-free. The integrability condition on -surface shows that
the (anti-)self-dual Weyl spinor can be described only by the covariant
derivative of the right-(left-)handed-torsion.Comment: 13 pages, Latex2e. The derivations and the conclusions are improve
Two quantum analogues of Fisher information from a large deviation viewpoint of quantum estimation
We discuss two quantum analogues of Fisher information, symmetric logarithmic
derivative (SLD) Fisher information and Kubo-Mori-Bogoljubov (KMB) Fisher
information from a large deviation viewpoint of quantum estimation and prove
that the former gives the true bound and the latter gives the bound of
consistent superefficient estimators. In another comparison, it is shown that
the difference between them is characterized by the change of the order of
limits.Comment: LaTeX with iopart.cls, iopart12.clo, iopams.st
CIRCULAR DICHROISM OF LIGHT-HARVESTING COMPLEXES FROM PURPLE PHOTOSYNTHETIC BACTERIA
The CD spectra of a range of antenna complexes from several different species of purple photosynthetic bacteria were recorded in the wavelength range of 190 to 930 nm. Analysis of the far UV CD (190 to 250 nm) showed that in each case except for the B800-850 from Chr. vinosum the secondary structure of the light-harvesting complexes contains a large amount of α-helix (50%) and very little 0-pleated sheet. This confirms the predictions of the group of Zuber of a high a-helical content based upon consideration of the primary structures of several antenna apoproteins. The CD spectra from the carotenoids and the bacteriochlorophylls show considerable variations depending upon the type of antenna complex. The different amplitude ratios in the CD spectrum for the bacteriochlorophyll Qy, Qx and Soret bands indicate not only different degrees of exciton coupling, but also a strong and variable hyperchromism (Scherz and Parson, 1984a, b)
Structure formation on the brane: A mimicry
We show how braneworld cosmology with bulk matter can explain structure
formation. In this scenario, the nonlocal corrections to the Friedmann
equations supply a Weyl fluid that can dominate over matter at late times due
to the energy exchange between the brane and the bulk. We demonstrate that the
presence of the Weyl fluid radically changes the perturbation equations, which
can take care of the fluctuations required to account for the large amount of
inhomogeneities observed in the local universe. Further, we show how this Weyl
fluid can mimic dark matter. We also investigate the bulk geometry responsible
for the scenario.Comment: 7 pages. Matches published versio
Ising pyrochlore magnets: Low temperature properties, ice rules and beyond
Pyrochlore magnets are candidates for spin-ice behavior. We present
theoretical simulations of relevance for the pyrochlore family R2Ti2O7 (R= rare
earth) supported by magnetothermal measurements on selected systems. By
considering long ranged dipole-dipole as well as short-ranged superexchange
interactions we get three distinct behaviours: (i) an ordered doubly degenerate
state, (ii) a highly disordered state with a broad transition to paramagnetism,
(iii) a partially ordered state with a sharp transition to paramagnetism. Thus
these competing interactions can induce behaviour very different from
conventional ``spin ice''. Closely corresponding behaviour is seen in the real
compounds---in particular Ho2Ti2O7 corresponds to case (iii) which has not been
discussed before, rather than (ii) as suggested earlier.Comment: 5 pages revtex, 4 figures; some revisions, additional data,
additional co-authors and a changed title. Basic ideas of paper remain the
same but those who downloaded the original version are requested to get this
more complete versio
Global information balance in quantum measurements
We perform an information-theoretical analysis of quantum measurement
processes and obtain the global information balance in quantum measurements, in
the form of a closed chain equation for quantum mutual entropies. Our balance
provides a tight and general entropic information-disturbance trade-off, and
explains the physical mechanism underlying it. Finally, the single-outcome
case, that is, the case of measurements with post-selection, is briefly
discussed.Comment: Final version to appear on Physical Review Letter
Asymptotic estimation theory for a finite dimensional pure state model
The optimization of measurement for n samples of pure sates are studied. The
error of the optimal measurement for n samples is asymptotically compared with
the one of the maximum likelihood estimators from n data given by the optimal
measurement for one sample.Comment: LaTeX, 23 pages, Doctoral Thesi
Compact F-theory GUTs with U(1)_PQ
We construct semi-local and global realizations of SU(5) GUTs in F-theory
that utilize a U(1)_PQ symmetry to protect against dimension four proton decay.
Symmetries of this type, which assign charges to H_u and H_d that forbid a tree
level \mu term, play an important role in scenarios for neutrino physics and
gauge mediation that have been proposed in local F-theory model building. As
demonstrated in arXiv:0906.4672, the presence of such a symmetry implies the
existence of non-GUT exotics in the spectrum, when hypercharge flux is used to
break the GUT group and to give rise to doublet-triplet splitting. These
exotics are of precisely the right type to solve the unification problem in
such F-theory models and might also comprise a non-standard messenger sector
for gauge mediation. We present a detailed description of models with U(1)_PQ
in the semi-local regime, which does not depend on details of any specific
Calabi-Yau four-fold, and then specialize to the geometry of arXiv:0904.3932 to
construct three-generation examples with the minimal allowed number of non-GUT
exotics. Among these, we find a handful of models in which the D3-tadpole
constraint can be satisfied without requiring the introduction of
anti-D3-branes. Finally, because SU(5) singlets that carry U(1)_PQ charge may
serve as candidate right-handed neutrinos or can be used to lift the exotics,
we study their origin in compact models and motivate a conjecture for how to
count their zero modes in a semi-local setting.Comment: 73 pages, 5 figures, v2: minor corrections to 4.3 and 6.3.1,
reference adde
Observation of direct hadronic pairs in nucleus-nucleus collisions in JACEE emulsion chambers
In a number of high energy ( or = 1 TeV/amu) nucleus-nucleus collisions observed in Japanese-American Cooperative Emulsion Experiment (JACEE) emulsion chambers, nonrandom spatial association of produced charged particles, mostly hadronic pairs, are observed. Similar narrow pairs are observed in about 100 events at much low energy (20 to 60 GeV/amu). Analysis shows that 30 to 50% of Pair abundances are understood by the Hambury-Brown-Twiss effect, and the remainder seems to require other explanations
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