49,484 research outputs found
A More Precise Extraction of |V_{cb}| in HQEFT of QCD
The more precise extraction for the CKM matrix element |V_{cb}| in the heavy
quark effective field theory (HQEFT) of QCD is studied from both exclusive and
inclusive semileptonic B decays. The values of relevant nonperturbative
parameters up to order 1/m^2_Q are estimated consistently in HQEFT of QCD.
Using the most recent experimental data for B decay rates, |V_{cb}| is updated
to be |V_{cb}| = 0.0395 \pm 0.0011_{exp} \pm 0.0019_{th} from B\to D^{\ast} l
\nu decay and |V_{cb}| = 0.0434 \pm 0.0041_{exp} \pm 0.0020_{th} from B\to D l
\nu decay as well as |V_{cb}| = 0.0394 \pm 0.0010_{exp} \pm 0.0014_{th} from
inclusive B\to X_c l \nu decay.Comment: 7 pages, revtex, 4 figure
A magnetized torus for modeling Sgr A* millimeter images and spectra
Context. The supermassive black hole, Sagittarius (Sgr) A*, in the centre of
our Galaxy has the largest angular size in the sky among all astrophysical
black holes. Its shadow, assuming no rotation, spans ~ 50 microarcsec.
Resolving such dimensions has long been out of reach for astronomical
instruments until a new generation of interferometers being operational during
this decade. Of particular interest is the Event Horizon Telescope (EHT) with
resolution ~ 20 microarcsec in the millimeter-wavelength range 0.87 mm - 1.3
mm. Aims. We investigate the ability of the fully general relativistic
Komissarov (2006) analytical magnetized torus model to account for observable
constraints at Sgr A* in the centimeter and millimeter domains. The impact of
the magnetic field geometry on the observables is also studied. Methods. We
calculate ray-traced centimeter- and millimeter-wavelength synchrotron spectra
and images of a magnetized accretion torus surrounding the central black hole
in Sgr A*. We assume stationarity, axial symmetry, constant specific angular
momentum and polytropic equation of state. A hybrid population of thermal and
non-thermal electrons is considered. Results. We show that the torus model is
capable of reproducing spectral constraints in the millimeter domain, and in
particular in the observable domain of the EHT. However, the torus model is not
yet able to fit the centimeter spectrum. 1.3 mm images at high inclinations are
in agreement with observable constraints. Conclusions. The ability of the torus
model to account for observations of Sgr A* in the millimeter domain is
interesting in the perspective of the future EHT. Such an analytical model
allows very fast computations. It will thus be a suitable test bed for
investigating large domains of physical parameters, as well as non-black-hole
compact object candidates and alternative theories of gravity.Comment: Major changes wrt the June 2014 version. Accepted by A&
Lepton flavor violating and conversion in unparticle physics
We have studied lepton flavor violation processes and
conversion in nuclei induced by unparticle. Both and conversion rate strongly
depend on the scale dimension and the unparticle coupling
(K=V, A, S, P). Present experimental upper bounds on
, and put stringent constraints on the parameters of unaprticle physics. The
scale dimensions around 2 are favored for the unparticle scale
of and the unparticle coupling of
. is proportional to
for the pure vector and scalar couplings between
unparticle and SM fermions, this peculiar atomatic number dependence can be
used to distinguish unparticle from other theoretical models.Comment: 16 pages, 5 figure
Soft Spin Wave Near nu=1: Evidence for a Magnetic Instability in Skyrmion Systems
The ground state of the two dimensional electron gas near =1 is
investigated by inelastic light scattering measurements carried down to very
low temperatures. Away from =1, the ferromagnetic spin wave collapses and
a new low-energy spin wave emerges below the Zeeman gap. The emergent spin wave
shows soft behavior as its energy increases with temperature and reaches the
Zeeman energy for temperatures above 2 K. The observed softening indicates an
instability of the two dimensional electron gas towards a magnetic order that
breaks spin rotational symmetry. We discuss our findings in light of the
possible existence of a Skyrme crystal.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
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