1,764 research outputs found
Hard X-ray imaging observation of fluctuating bursts
Measurements were done to obtain the one-dimensional sizes of rapidly fluctuating bursts with fast spikes whose rise times are typically about one second, and in some extreme cases less than 0.1 second. The results of two bursts with fast spikes are presented. One has a soft spectrum, and the other has a very hard spectrum. The measured one-dimensional size of both events indicates relatively a small size and simple structure. It can be said, however, that the source size is not so small as expected from its rapid time variations. Therefore, a thermal explanation of these bursts seems to be excluded
The strange quark condensate in the nucleon in 2+1 flavor QCD
We calculate the "strange quark content of the nucleon", ,
which is important for interpreting the results of some dark matter detection
experiments. The method is to evaluate quark-line disconnected correlations on
the MILC lattice ensembles, which include the effects of dynamical strange
quarks. After continuum and chiral extrapolations, the result is <N |s s_bar
|N> = 0.69 +- 0.07(statistical) +- 0.09(systematic), in the modified minimal
subtraction scheme (2 GeV), or for the renormalization scheme invariant form,
m_s partial{M_N}/partial{m_s} = 59(6)(8) MeV.Comment: Added figures and references, especially for fit range choice. Other
changes for clarity. Version to appear in publicatio
Light Quark Mass Reweighting
We present a systematic study of the effectiveness of light quark mass
reweighting. This method allows a single lattice QCD ensemble, generated with a
specific value of the dynamical light quark mass, to be used to determine
results for other, nearby light dynamical quark masses. We study two gauge
field ensembles generated with 2+1 flavors of dynamical domain wall fermions
with light quark masses m_l=0.02 (m_\pi=620 MeV) and m_l=0.01 (m_\pi=420 MeV).
We reweight each ensemble to determine results which could be computed directly
from the other and check the consistency of the reweighted results with the
direct results. The large difference between the 0.02 and 0.01 light quark
masses suggests that this is an aggressive application of reweighting as can be
seen from fluctuations in the magnitude of the reweighting factor by four
orders of magnitude. Never-the-less, a comparison of the reweighed topological
charge, average plaquette, residual mass, pion mass, pion decay constant, and
scalar correlator between these two ensembles shows agreement well described by
the statistical errors. The issues of the effective number of configurations
and finite sample size bias are discussed. An examination of the topological
charge distribution implies that it is more favorable to reweight from heavier
mass to lighter quark mass.Comment: 24 pages and 10 figure
Dark matter in the classically conformal B-L model
When the classically conformal invariance is imposed on the minimal gauged
B-L extended Standard Model (SM), the B-L gauge symmetry is broken by the
Coleman-Weinberg mechanism naturally at the TeV scale. Introducing a new Z_2
parity in the model, we investigate phenomenology of a right-handed neutrino
dark matter whose stability is ensured by the parity. We find that the relic
abundance of the dark matter particle can be consistent with the observations
through annihilation processes enhanced by resonances of either the SM Higgs
boson, the B-L Higgs boson or the B-L gauge boson (Z' boson). Therefore, the
dark matter mass is close to half of one of these boson masses. Due to the
classically conformal invariance and the B-L gauge symmetry breaking via the
Coleman-Weinberg mechanism, Higgs boson masses, Z' boson mass and the dark
matter mass are all related, and we identify the mass region to be consistent
with experimental results. We also calculate the spin-independent cross section
of the dark matter particle off with nucleon and discuss implications for
future direct dark matter search experiments.Comment: 13 pages, 4 figure
Search for Higgs Bosons in SUSY Cascade Decays and Neutralino Dark Matter
The Minimal Supersymmetric Extension of the Standard Model (MSSM) is a well
motivated theoretical framework, which contains an extended Higgs sector,
including a light Higgs with Standard Model-like properties in most of the
parameter space. Due to the large QCD background, searches for such a Higgs,
decaying into a pair of bottom quarks, is very challenging at the LHC. It has
been long realized that the situation may be ameliorated by searching for Higgs
bosons in supersymmetric decay chains. Moreover, it has been recently suggested
that the bobber decay channel may be observed in standard production channels
by selecting boosted Higgs bosons, which may be easily identified from the QCD
background. Such boosted Higgs bosons are frequent in the MSSM, since they are
produced from decays of heavy colored supersymmetric particles. Previous works
have emphasized the possibility of observing boosted Higgs bosons in the light
higgsino region. In this work, we study the same question in the regions of
parameter space consistent with a neutralino dark matter relic density,
analyzing its dependence on the non-standard Higgs boson, slepton and squark
masses, as well as on the condition of gaugino mass unification. In general, we
conclude that, provided sleptons are heavier than the second lightest
neutralinos, the presence of boosted Higgs is a common MSSM feature, implying
excellent prospects for observation of the light MSSM Higgs boson in the near
future.Comment: 30 pages, 9 figures. v2: New Xenon 100 results implemented, version
to appear in PR
Demonstration of Robust Quantum Gate Tomography via Randomized Benchmarking
Typical quantum gate tomography protocols struggle with a self-consistency
problem: the gate operation cannot be reconstructed without knowledge of the
initial state and final measurement, but such knowledge cannot be obtained
without well-characterized gates. A recently proposed technique, known as
randomized benchmarking tomography (RBT), sidesteps this self-consistency
problem by designing experiments to be insensitive to preparation and
measurement imperfections. We implement this proposal in a superconducting
qubit system, using a number of experimental improvements including
implementing each of the elements of the Clifford group in single `atomic'
pulses and custom control hardware to enable large overhead protocols. We show
a robust reconstruction of several single-qubit quantum gates, including a
unitary outside the Clifford group. We demonstrate that RBT yields physical
gate reconstructions that are consistent with fidelities obtained by randomized
benchmarking
The intrinsic strangeness and charm of the nucleon using improved staggered fermions
We calculate the intrinsic strangeness of the nucleon, - ,
using the MILC library of improved staggered gauge configurations using the
Asqtad and HISQ actions. Additionally, we present a preliminary calculation of
the intrinsic charm of the nucleon using the HISQ action with dynamical charm.
The calculation is done with a method which incorporates features of both
commonly-used methods, the direct evaluation of the three-point function and
the application of the Feynman- Hellman theorem. We present an improvement on
this method that further reduces the statistical error, and check the result
from this hybrid method against the other two methods and find that they are
consistent. The values for and found here, together with
perturbative results for heavy quarks, show that dark matter scattering through
Higgs-like exchange receives roughly equal contributions from all heavy quark
flavors.Comment: 17 pages, 14 figure
Determination of B*B pi coupling in unquenched QCD
The coupling is a fundamental parameter of chiral effective
Lagrangian with heavy-light mesons and can constrain the chiral behavior of
, and the form factor in the soft pion limit. We
compute the coupling with the static heavy quark and the
-improved Wilson light quark. Simulations are carried out with
unquenched lattices at and
lattices at generated by CP-PACS collaboration. To improve the
statistical accuracy, we employ the all-to-all propagator technique and the
static quark action with smeared temporal link variables following the quenched
study by Negishi {\it et al.}. These methods successfully work also on
unquenched lattices, and determine the coupling with 1--2%
statistical accuracy on each lattice spacing.Comment: 19pages,26figure
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