153 research outputs found
Evolution of Ligia Isopods in three Geologically Dynamic Regions
The oniscidean genus Ligia has a cosmopolitan distribution, occurring mainly in rocky supralittoral habitats, although a few species are found in tropical mountain freshwater habitats. The long-distance dispersal potential of the coastal Ligia isopods is very limited, due to a series of biological characteristics, which contributes to a high isolation of their populations. Consistent with this, high levels of allopatric differentiation have been detected for coastal Ligia in different parts of the world, with phylogeographic patterns exhibiting signatures of past geological and oceanographic events. In this dissertation, we used mitochondrial and nuclear gene sequences to infer phylogeographic patterns of Ligia isopods in the Hawaiian archipelago, and the region comprised by the Caribbean Sea and the Eastern Pacific coast of Colombia and Central America. We also conducted geometric-morphometric analyses to determine whether differences in overall body shape exist between divergent lineages in coastal Ligia from the Hawaiian archipelago and from the region between Central California and Central Mexico, including the Gulf of California. We observed that Ligia populations from the Caribbean Sea and the Pacific coast of Central America and Colombia, as well as those from the Hawaiian archipelago, harbor highly divergent lineages, suggesting that the Ligia species recognized for these regions represent cryptic species complexes. Phylogeographic patterns suggest that passive overwater dispersal has been an important factor shaping the evolutionary history of Ligia in these two regions. Geometric morphometric approaches uncovered morphological differences between highly divergent genetic lineages of Ligia isopods in the Hawaiian archipelago and the region between Central California and Central Mexico, including the Gulf of California. Large overlap in body shapes occur, however, suggesting overall body shape evolution is somewhat constrained and this character is unreliable for taxonomic distinction of these lineages
Probing neutrino properties with charged scalar lepton decays
Supersymmetry with bilinear R-parity violation provides a predictive
framework for neutrino masses and mixings in agreement with current neutrino
oscillation data. The model leads to striking signals at future colliders
through the R-parity violating decays of the lightest supersymmetric particle.
Here we study charged scalar lepton decays and demonstrate that if the scalar
tau is the LSP (i) it will decay within the detector, despite the smallness of
the neutrino masses, (ii) the relative ratio of branching ratios Br({tilde
tau}_1 --> e sum nu_i)/ Br({tilde tau}_1 --> mu sum nu_i) is predicted from the
measured solar neutrino angle, and (iii) scalar muon and scalar electron decays
will allow to test the consistency of the model. Thus, bilinear R-parity
breaking SUSY will be testable at future colliders also in the case where the
LSP is not the neutralino.Comment: 24 pages, 8 ps figs Report-no.: IFIC/02-33 and ZU-TH 11/0
Spontaneous R-Parity violation bounds
We investigate bounds from tree-level and one-loop processes in generic
supersymmetric models with spontaneous R-parity breaking in the superpotential.
We analyse the bounds from a general point of view. The bounds are applicable
both for all models with spontaneous R-parity violation and for explicit
bilinear R-parity violation based on general lepton-chargino and
neutrino-neutralino mixings. We find constraints from semileptonic B, D and K
decays, leptonic decays of the mu and tau, electric dipole moments, as well as
bounds for the anomalous magnetic moment of the muon.Comment: 22 page
A Complex Evolutionary History in a Remote Archipelago: Phylogeography and Morphometrics of the Hawaiian Endemic Ligia Isopods
Compared to the striking diversification and levels of endemism observed in many terrestrial groups within the Hawaiian Archipelago, marine invertebrates exhibit remarkably lower rates of endemism and diversification. Supralittoral invertebrates restricted to specific coastal patchy habitats, however, have the potential for high levels of allopatric diversification. This is the case of Ligia isopods endemic to the Hawaiian Archipelago, which most likely arose from a rocky supralittoral ancestor that colonized the archipelago via rafting, and diversified into rocky supralittoral and inland lineages. A previous study on populations of this isopod from Oʻahu and Kauaʻi revealed high levels of allopatric differentiation, and suggested inter-island historical dispersal events have been rare. To gain a better understanding on the diversity and evolution of this group, we expanded prior phylogeographic work by incorporating populations from unsampled main Hawaiian Islands (Maui, Molokaʻi, Lanaʻi, and Hawaiʻi), increasing the number of gene markers (four mitochondrial and two nuclear genes), and conducting Maximum likelihood and Bayesian phylogenetic analyses. Our study revealed new lineages and expanded the distribution range of several lineages. The phylogeographic patterns of Ligia in the study area are complex, with Hawaiʻi, Oʻahu, and the Maui-Nui islands sharing major lineages, implying multiple inter-island historical dispersal events. In contrast, the oldest and most geographically distant of the major islands (Kauaʻi) shares no lineages with the other islands. Our results did not support the monophyly of all the supralittoral lineages (currently grouped into L. hawaiensis), or the monophyly of the terrestrial lineages (currently grouped into L. perkinsi), implying more than one evolutionary transition between coastal and inland forms. Geometric-morphometric analyses of three supralittoral clades revealed significant body shape differences among them. A taxonomic revision of Hawaiian Ligia is warranted. Our results are relevant for the protection of biodiversity found in an environment subject to high pressure from disturbances.The open access fee for this work was funded through the Texas A&M University Open Access to Knowledge (OAK) Fund
Broken R-parity, stop decays, and neutrino physics
We discuss the phenomenology of the lightest stop in models where R-parity is
broken by bilinear superpotential terms. In this class of models we consider
scenarios where the R-parity breaking two-body decay ~t_1->\tau^+b competes
with the leading three-body decays such as ~t_1->W^+b~\chi^0_1. We demonstrate
that the R-parity violating decay can be sizable and in some parts of the
parameter space even the dominant one. Moreover we discuss the expectations for
\~t_1->\mu^+b and ~t_1->e^+b. The recent results from solar and atmospheric
neutrinos suggest that these are as important as the tau bottom mode. The
\~t_1->l^+b decays are of particular interest for hadron colliders, as they may
allow a full mass reconstruction of the lighter stop. Moreover these decay
modes allow cross checks on the neutrino mixing angle involved in the solar
neutrino puzzle complementary to those possible using neutralino decays. For
the so--called small mixing angle or SMA solution ~t_1->e^+b should be
negligible, while for the large mixing angle type solutions all ~t_1->l^+b
decays should have comparable magnitude.Comment: 51 pages, 6 figures, LaTeX2e and RevTeX4, published versio
Reconstructing Neutrino Properties from Collider Experiments in a Higgs Triplet Neutrino Mass Model
We extend the minimal supersymmetric standard model with bilinear R-parity
violation to include a pair of Higgs triplet superfields. The neutral
components of the Higgs triplets develop small vacuum expectation values (VEVs)
quadratic in the bilinear R-parity breaking parameters. In this scheme the
atmospheric neutrino mass scale arises from bilinear R-parity breaking while
for reasonable values of parameters the solar neutrino mass scale is generated
from the small Higgs triplet VEVs. We calculate neutrino masses and mixing
angles in this model and show how the model can be tested at future colliders.
The branching ratios of the doubly charged triplet decays are related to the
solar neutrino angle via a simple formula.Comment: 19 pages, 4 figures; one formula corrected, two author's names
corrected; some explanatory comments adde
Neutrino Masses and Mixings from Supersymmetry with Bilinear R--Parity Violation: A Theory for Solar and Atmospheric Neutrino Oscillations
The simplest unified extension of the MSSM with bi-linear R--Parity violation
naturally predicts a hierarchical neutrino mass spectrum, in which one neutrino
acquires mass by mixing with neutralinos, while the other two get mass
radiatively. We have performed a full one-loop calculation of the
neutralino-neutrino mass matrix in the bi-linear \rp MSSM, taking special care
to achieve a manifestly gauge invariant calculation. Moreover we have performed
the renormalization of the heaviest neutrino, needed in order to get meaningful
results. The atmospheric mass scale and maximal mixing angle arise from
tree-level physics, while solar neutrino scale and oscillations follow from
calculable one-loop corrections. If universal supergravity assumptions are made
on the soft-supersymmetry breaking terms then the atmospheric scale is
calculable as a function of a single \rp violating parameter by the
renormalization group evolution due to the non-zero bottom quark Yukawa
coupling. The solar neutrino problem must be accounted for by the small mixing
angle (SMA) MSW solution. If these assumptions are relaxed then one can
implement large mixing angle solutions, either MSW or just-so. The theory
predicts the lightest supersymmetic particle (LSP) decay to be observable at
high-energy colliders, despite the smallness of neutrino masses indicated by
experiment. This provides an independent way to test this solution of the
atmospheric and solar neutrino anomalies.Comment: 46 pages, references added + several misprints correcte
Solar Neutrino Masses and Mixing from Bilinear R-Parity Broken Supersymmetry: Analytical versus Numerical Results
We give an analytical calculation of solar neutrino masses and mixing at
one-loop order within bilinear R-parity breaking supersymmetry, and compare our
results to the exact numerical calculation. Our method is based on a systematic
perturbative expansion of R-parity violating vertices to leading order. We find
in general quite good agreement between approximate and full numerical
calculation, but the approximate expressions are much simpler to implement. Our
formalism works especially well for the case of the large mixing angle MSW
solution (LMA-MSW), now strongly favoured by the recent KamLAND reactor
neutrino data.Comment: 34 pages, 14 ps figs, some clarifying comments adde
Testing neutrino mixing at future collider experiments
Low energy supersymmetry with bilinear breaking of R-parity leads to a
weak-scale seesaw mechanism for the atmospheric neutrino scale and a radiative
mechanism for the solar neutrino scale. The model has striking implications for
collider searches of supersymmetric particles. Assuming that the lightest SUSY
particle is the lightest neutralino we demonstrate that (i) The neutralino
decays inside the detector even for tiny neutrino masses. (ii) Measurements of
the neutrino mixing angles lead to predictions for the ratios of various
neutralino branching ratios implying an independent test of neutrino physics at
future colliders, such as the Large Hadron Collider or a Linear Collider.Comment: LaTex, 35 pages, 20 figures included, version 2, section on model
shortened, Fig. 13 replaced, typos corrected, version to appear in Phys.Rev.
Present and Future Bounds on Non-Standard Neutrino Interactions
We consider Non-Standard neutrino Interactions (NSI), described by
four-fermion operators of the form , where is an electron or first generation quark. We
assume these operators are generated at dimension , so the related
vertices involving charged leptons, obtained by an SU(2) transformation
, do not appear at tree level. These related
vertices necessarily arise at one loop, via exchange. We catalogue current
constraints from measurements in neutrino scattering, from
atmospheric neutrino observations, from LEP, and from bounds on the related
charged lepton operators. We estimate future bounds from comparing KamLAND and
solar neutrino data, and from measuring at the near detector
of a neutrino factory. Operators constructed with and should
not confuse the determination of oscillation parameters at a factory,
because the processes we consider are more sensitive than oscillations at the
far detector. For operators involving , we estimate similar
sensitivities at the near and far detector.Comment: Erratum added at the end of the documen
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