26,344 research outputs found
M87 black hole mass and spin estimate through the position of the jet boundary shape break
We propose a new method of estimating a mass of a super massive black hole
residing in the center of an active galaxy. The active galaxy M87 offers a
convenient test case for the method due to the existence of a large amount of
observational data on the jet and ambient environment properties in the central
area of the object. We suggest that the observed transition of a jet boundary
shape from a parabolic to a conical form is associated with the flow transiting
from the magnetically dominated regime to the energy equipartition between
plasma bulk motion and magnetic field. By coupling the unique set of
observations available for the jet kinematics, environment and boundary profile
with our MHD modelling under assumption on the presence of a dynamically
important magnetic field in the M87 jet, we estimate the central black hole
mass and spin. The method leads us to believe that the M87 super massive black
hole has a mass somewhat larger than typically accepted so far.Comment: 10 pages, 1 figure, 3 tables, accepted for publication by MNRA
Decoherence due to discrete noise in Josephson qubits
We study decoherence produced by a discrete environment on a charge Josephson
qubit by introducing a model of an environment of bistable fluctuators. In
particular we address the effect of noise where memory effects play an
important role. We perform a detailed investigation of various computation
procedures (single shot measurements, repeated measurements) and discuss the
problem of the information needed to characterize the effect of the
environment. Although in general information beyond the power spectrum is
needed, in many situations this results in the knowledge of only one more
microscopic parameter of the environment. This allows to determine which
degrees of freedom of the environment are effective sources of decoherence in
each different physical situation considered.Comment: 20 pages, 11 figure
Observation of discrete energy levels in a quantum confined system
Low temperature scanning tunneling microscope images and spectroscopic data
have been obtained on subnanometer size Pb clusters fabricated using the
technique of buffer layer assisted growth. Discrete energy levels were resolved
in current-voltage characteristics as current peaks rather than current steps.
Distributions of peak voltage spacings and peak current heights were consistent
with Wigner-Dyson and Porter-Thomas distributions respectively, suggesting the
relevance of random matrix theory to the description of the electronic
eigenstates of the clusters. The observation of peaks rather than steps in the
current-voltage characteristics is attributed to a resonant tunneling process
involving the discrete energy levels of the cluster, the tip, and the states at
the interface between the cluster and the substrate surface.Comment: 4 pages, 4 figure
The electric dipole moment of the nucleon from simulations at imaginary vacuum angle theta
We compute the electric dipole moment of proton and neutron from lattice QCD
simulations with N_f=2 flavors of dynamical quarks at imaginary vacuum angle
theta. The calculation proceeds via the CP odd form factor F_3. A novel feature
of our calculation is that we use partially twisted boundary conditions to
extract F_3 at zero momentum transfer. As a byproduct, we test the QCD vacuum
at nonvanishing theta.Comment: 22 pages, 10 figure
Improving the lattice axial vector current
For Wilson and clover fermions traditional formulations of the axial vector
current do not respect the continuum Ward identity which relates the divergence
of that current to the pseudoscalar density. Here we propose to use a
point-split or one-link axial vector current whose divergence exactly satisfies
a lattice Ward identity, involving the pseudoscalar density and a number of
irrelevant operators. We check in one-loop lattice perturbation theory with
SLiNC fermion and gauge plaquette action that this is indeed the case including
order effects. Including these operators the axial Ward identity remains
renormalisation invariant. First preliminary results of a nonperturbative check
of the Ward identity are also presented.Comment: 7 pages, 3 figures, Proceedings of the 33rd International Symposium
on Lattice Field Theory, 14-18 July 2015, Kobe, Japa
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