11,734 research outputs found
Incidental Catch of Marine Mammals by Foreign and Joint Venture Trawl Vessels in the U.S. EEZ of the North Pacific, 1973-88
During 1973-88, 3,661 marine mammals of 17 species were reported as incidental catch by U.S. fishery observers aboard foreign and joint venture trawl vessels in the U.S.
Exclusive Economic Zone in the North Pacific Ocean and the Bering Sea. Northern sea lions (Eumetopias jubatus) accounted for 90% of the reported incidental mortality in the Gulf of Alaska and eastern Bering Sea. Nearly half of these sea lions were taken in trawl nets in the Shelikof Strait, Alaska, joint venture fishery during 1982-84. However, high incidental mortality rates (>25 sea lions per 10,000 metric tons of groundfish catch) also occurred in the foreign fisheries near Kodiak Island and in the Aleutian Islands area in earlier years. Estimated annual mortality of incidentally caught northern sea lions in
Alaska declined from 1,000 to 2,000 animals per year during the early 1970s and 1982 to fewer than 100 animals in 1988. In the Bering Sea most sea lions incidentally caught were
males, while in the Gulf of Alaska females were more frequently caught. Females may also have been dominant in the incidental catch of sea lions in the Aleutian Islands area, but age and sex composition data are limited. Incidental mortality of adult female sea lions by foreign trawl fisheries in these areas could have partially contributed to the reported declines in northern sea lion populations in Alaska during the 1970s, but it cannot alone
account for the present decline in population size. (PDF file contains 64 pages.
Theory for Baryon Number and Dark Matter at the LHC
We investigate the possibility to test the simplest theory for spontaneous
baryon number violation at the Large Hadron Collider. In this context the
baryon number is a local gauge symmetry spontaneously broken at the low scale
through the Brout-Englert-Higgs mechanism. This theory predicts the existence
of a leptophobic neutral gauge boson and a fermionic dark matter candidate with
baryon number. We study the gauge boson and Higgs decays, and explore the
connection between collider signatures and constraints coming from dark matter
experiments. We point out an upper bound on the symmetry breaking scale using
the relic density constraints which tells us that this model can be tested or
ruled out at current or future collider experiments.Comment: 30 pages, 9 figures, typos corrected, new appendix, version to appear
in PR
Baryonic Dark Matter
We investigate a simple extension of the Standard Model where the baryon
number is a local gauge symmetry and the cold dark matter in the Universe can
be described by a fermionic field with baryon number. We refer to this scenario
as "Baryonic Dark Matter''. The stability of the dark matter candidate is a
natural consequence of the spontaneous breaking of baryon number at the low
scale and there is no need to impose an extra discrete symmetry. The
constraints from the relic density and the predictions for direct detection are
discussed in detail. We briefly discuss the testability of this model using the
correlation between the Large Hadron Collider data and possible results from
dark matter experiments.Comment: to appear in Physics Letters
The inverse eigenvalue problem for quantum channels
Given a list of n complex numbers, when can it be the spectrum of a quantum
channel, i.e., a completely positive trace preserving map? We provide an
explicit solution for the n=4 case and show that in general the
characterization of the non-zero part of the spectrum can essentially be given
in terms of its classical counterpart - the non-zero spectrum of a stochastic
matrix. A detailed comparison between the classical and quantum case is given.
We discuss applications of our findings in the analysis of time-series and
correlation functions and provide a general characterization of the peripheral
spectrum, i.e., the set of eigenvalues of modulus one. We show that while the
peripheral eigen-system has the same structure for all Schwarz maps, the
constraints imposed on the rest of the spectrum change immediately if one
departs from complete positivity.Comment: 16 page
Gamma Lines from Majorana Dark Matter
We discuss simple models which predict the existence of significant gamma-ray
fluxes from dark matter annihilation. In this context the dark matter candidate
is a Majorana fermion with velocity-suppressed tree-level annihilation into
Standard Model fermions but unsuppressed annihilation into photons. These gamma
lines can easily be distinguished from the continuum and provide a possibility
to test these models.Comment: 6 pages, 4 figures, version to appear in PR
New Forces and the 750 GeV Resonance
Recently, the ATLAS and CMS collaborations have pointed out the possible
existence of a new resonance with a mass around 750 GeV. We investigate the
possibility to identify this new resonance with a spin zero field responsible
for the breaking of a new gauge symmetry. We focus on a simple theory where the
baryon number is a local symmetry spontaneously broken at the low scale. In
this context new vector-like quarks are needed to cancel all baryonic anomalies
and define the production mechanism and decays of the new Higgs at the LHC.
Assuming the existence of the new Higgs with a mass of 750 GeV at the LHC we
find an upper bound on the symmetry breaking scale. Therefore, one expects that
a new force associated with baryon number could be discovered at the LHC.Comment: 19 pages, 6 figure
Baryonic Higgs at the LHC
We investigate the possible collider signatures of a new Higgs in simple
extensions of the Standard Model where baryon number is a local symmetry
spontaneously broken at the low scale. We refer to this new Higgs as "Baryonic
Higgs". This Higgs has peculiar properties since it can decay into all Standard
Model particles, the leptophobic gauge boson, and the vector-like quarks
present in these theories to ensure anomaly cancellation. We investigate in
detail the constraints from the , , , and
searches at the Large Hadron Collider, needed to find a lower bound on the
scale at which baryon number is spontaneously broken. The di-photon channel
turns out to be a very sensitive probe in the case of small scalar mixing and
can severely constrain the baryonic scale. We also study the properties of the
leptophobic gauge boson in order to understand the testability of these
theories at the LHC.Comment: 20 pages, 9 figures; minor corrections, to appear in JHE
Left-Right Symmetric Theory with Light Sterile Neutrinos
A simple theoretical framework for the spontaneous breaking of parity, baryon
and lepton numbers is proposed. In this context, the baryon and lepton numbers
are independent local gauge symmetries, while parity is defined making use of
the left-right symmetry. We show that in the minimal model the new leptoquark
fields needed to define an anomaly-free theory also generate neutrino masses
through the type III seesaw mechanism. The spectrum of neutrinos and some
phenomenological aspects are discussed. This theory predicts the possible
existence of two light sterile neutrinos.Comment: minor corrections, published in Physical Review D as a Rapid
Communicatio
Gamma-Ray Excess and the Minimal Dark Matter Model
We point out that the gamma-ray excesses in the galactic center and in the
dwarf galaxy Reticulum II can both be well explained within the simplest dark
matter model. We find that the corresponding region of parameter space will be
tested by direct and indirect dark matter searches in the near future.Comment: 6 pages, 8 figures; v2: new LUX bounds included, to appear in JHE
Scalar Singlet Dark Matter and Gamma Lines
We point out the possibility to test the simplest scalar dark matter model at
gamma-ray telescopes. We discuss the relevant constraints and show the
predictions for direct detection, gamma line searches and LHC searches. Since
the final state radiation processes are suppressed by small Yukawa couplings
one could observe the gamma lines from dark matter annihilation.Comment: new references, to appear in Physics Letters
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