484 research outputs found
Management Options for the Inland Fisheries Resource in South Sumatra, Indonesia: I Bioeconomic Model
The inland fishery in South Sumatra, Indonesia, is an important source of income, employment and protein to small-scale fishers. Some overall indicators, such as virtual disappearance of certain important species and continuous reduction in the size of harvested fish, indicate that the fishery is not being exploited on a sustainable basis. In this study, an evaluation of the status of the existing fish stock is undertaken, and an analytical model for identifying efficient levels of exploitation of the fishery is developed. Primary data are used to describe the current costs of fishing effort. Secondary data, combined with results of analysis of primary data, are then used to derive a supply function for the fishery. Different types of fishing gear are standardised into a single type of fishing unit, and mixed species of harvested fish are treated as an aggregated fish stock. Empirical results reveal that both riverine and swamp fisheries in South Sumatra were biologically and economically over-fished during the period of study. This implies that regulation is required to reduce the level of fishing effort.smallholder fisheries, bioeconomic analysis, Inland fisheries, Indonesia, Sumatra, Resource /Energy Economics and Policy,
New Physics Effects in Higgs Decay to Tau Leptons
We study the possible effects of TeV scale new physics (NP) on the rate for
Higgs boson decays to charged leptons, focusing on the tau tau channel which
can be readily studied at the Large Hadron collider. Using an SU(3)_C X SU(2)_L
X U(1)_Y invariant effective theory valid below a NP scale Lambda, we determine
all effective operators up to dimension six that could generate appreciable
contributions to the decay rate and compute the dependence of the rate on the
corresponding operator coefficients. We bound the size of these operator
coefficients based on the scale of the tau mass, naturalness considerations,
and experimental constraints on the tau anomalous magnetic moment. These
considerations imply that contributions to the decay rate from a NP scale
Lambda ~ TeV could be comparable to the prediction based on the SM Yukawa
interaction. A reliable test of the Higgs mechanism for fermion mass generation
via the h-> tau tau channel is possible only after such NP effects are
understood and brought under theoretical control.Comment: 10 pages, 6 figures, V2: typos correcte
Implications of a scalar dark force for terrestrial experiments
A long-range intergalactic force between dark matter (DM) particles, mediated by an ultralight scalar, is tightly constrained by galactic dynamics and large scale structure formation. We examine the implications of such a ‘‘dark force” for several terrestrial experiments, including Eötvös tests of the Weak Equivalence Principle (WEP), direct-detection DM searches, and collider studies. The presence of a dark force implies a nonvanishing effect in Eötvös tests that could be probed by current and future experiments depending on the DM model. For scalar DM that is a singlet under the standard model gauge groups, a dark force of astrophysically relevant magnitude is ruled out in large regions of parameter space by the DM relic density and WEP constraints. WEP tests also imply constraints on the Higgs-exchange contributions to the spin-independent (SI) DM-nucleus direct-detection cross section. For WIMP scenarios, these considerations constrain Higgs-exchange contributions to the SI cross section to be subleading compared to gauge-boson mediated contributions. In multicomponent DM scenarios, a dark force would preclude large shifts in the rate for Higgs decay to two photons associated with DM-multiplet loops that might otherwise lead to measurable deviations at the LHC or a future linear collider. The combination of observations from galactic dynamics, large scale structure formation, Eötvös experiments, DM-direct-detection experiments, and colliders can further constrain the size of new long-range forces in the dark sector
Parity-Violating Electron-Deuteron Scattering with a Twist
We show that Parity-Violating Deep Inelastic Scattering (PVDIS) of
longitudinally polarized electrons from deuterium can in principle be a
relatively clean probe of higher twist quark-quark correlations beyond the
parton model. As first observed by Bjorken and Wolfenstein, the dominant
contribution to the electron polarization asymmetry, proportional to the axial
vector electron coupling, receives corrections at twist-four from the matrix
element of a single four-quark operator. We reformulate the Bjorken/Wolfenstein
argument in a matter suitable for the interpretation of experiments planned at
the Thomas Jefferson National Accelerator Facility (JLab). In particular, we
observe that because the contribution of the relevant twist four operator
satisfies the Callan-Gross relation, the ratio of parity-violating longitudinal
and transverse cross sections, R_{\gamma Z}, is identical to that for purely
electromagnetic scattering, R_{\gamma}, up to perturbative and power suppressed
contributions. This result simplifies the interpretation of the asymmetry in
terms of other possible novel hadronic and electroweak contributions. We use
the results of MIT Bag Model calculations to estimate contributions of the
relevant twist four operator to the leading term in the asymmetry as a function
of Bjorken x and Q2 . We compare these estimates with possible leading twist
corrections due to violation of charge symmetry in the parton distribution
functions.Comment: 27 pages, 3 figures, typos fixed, version accepted for publication in
Physical Review
Adsorption properties and third sound propagation in superfluid He films on carbon nanotubes
We consider the adsorption properties of superfluid He films on carbon
nanotubes. One major factor in the adsorption is the surface tension force
arising from the very small diameter of the nanotubes. Calculations show that
surface tension keeps the film thickness on the tubes very thin even when the
helium vapor is increased to the saturated pressure. The weakened Van der Waals
force due to the cylindrical geometry also contributes to this. Both of these
effects act to lower the predicted velocity of third sound propagation along
the tubes. It does not appear that superfluidity will be possible on
single-walled nanotubes of diameter about one nm, since the film thickness is
less than 3 atomic layers even at saturation. Superfluidity is possible on
larger-diameter nanotube bundles and multi-walled nanotubes, however. We have
observed third sound signals on nanotube bundles of average diameter 5 nm which
are sprayed onto a Plexiglass surface, forming a network of tubes.Comment: 4 pages, accepted for Journal of Physics: Conference Series
(Proceedings of LT25
Factorization and Resummation of Higgs Boson Differential Distributions in Soft-Collinear Effective Theory
We derive a factorization theorem for the Higgs boson transverse momentum
(p_T) and rapidity (Y) distributions at hadron colliders, using the Soft
Collinear Effective Theory (SCET), for m_h>> p_T>> \Lambda_{QCD} where m_h
denotes the Higgs mass. In addition to the factorization of the various scales
involved, the perturbative physics at the p_T scale is further factorized into
two collinear impact-parameter Beam Functions (iBFs) and an inverse Soft
Function (iSF). These newly defined functions are of a universal nature for the
study of differential distributions at hadron colliders. The additional
factorization of the p_T-scale physics simplifies the implementation of higher
order radiative corrections in \alpha_s(p_T). We derive formulas for
factorization in both momentum and impact parameter space and discuss the
relationship between them. Large logarithms of the relevant scales in the
problem are summed using the renormalization group equations of the effective
theories. Power corrections to the factorization theorem in p_T/m_h and
\Lambda_{QCD}/p_T can be systematically derived. We perform multiple
consistency checks on our factorization theorem including a comparison with
known fixed order QCD results. We compare the SCET factorization theorem with
the Collins-Soper-Sterman approach to low-p_T resummation.Comment: 66 pages, 5 figures, discussion regarding zero-bin subtractions adde
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