13,894 research outputs found
Vevacious: A Tool For Finding The Global Minima Of One-Loop Effective Potentials With Many Scalars
Several extensions of the Standard Model of particle physics contain
additional scalars implying a more complex scalar potential compared to that of
the Standard Model. In general these potentials allow for charge and/or color
breaking minima besides the desired one with correctly broken SU(2)_L times
U(1)_Y . Even if one assumes that a metastable local minimum is realized, one
has to ensure that its lifetime exceeds that of our universe. We introduce a
new program called Vevacious which takes a generic expression for a one-loop
effective potential energy function and finds all the tree-level extrema, which
are then used as the starting points for gradient-based minimization of the
one-loop effective potential. The tunneling time from a given input vacuum to
the deepest minimum, if different from the input vacuum, can be calculated. The
parameter points are given as files in the SLHA format (though is not
restricted to supersymmetric models), and new model files can be easily
generated automatically by the Mathematica package SARAH. This code uses
HOM4PS2 to find all the minima of the tree-level potential, PyMinuit to follow
gradients to the minima of the one-loop potential, and CosmoTransitions to
calculate tunneling times.Comment: 44 pages, 1 figure, manual for publicly available software, v2
corresponds to version accepted for publication in EPJC [clearer explanation
of scale dependence and region of validity, explicit mention that SLHA files
should have blocks matching those expected by model files, updated
references
Constraining the Natural MSSM through tunneling to color-breaking vacua at zero and non-zero temperature
We re-evaluate the constraints on the parameter space of the minimal
supersymmetric standard model from tunneling to charge- and/or color-breaking
minima, taking into account thermal corrections. We pay particular attention to
the region known as the Natural MSSM, where the masses of the scalar partners
of the top quarks are within an order of magnitude or so of the electroweak
scale. These constraints arise from the interaction between these scalar tops
and the Higgs fields, which allows the possibility of parameter points having
deep charge- and color-breaking true vacua. In addition to requiring that our
electro-weak-symmetry-breaking, yet QCD- and electromagnetism-preserving vacuum
has a sufficiently long lifetime at zero temperature, also demanding stability
against thermal tunneling further restricts the allowed parameter space.Comment: 7 pages, 2 figures, software available from
http://vevacious.hepforge.org/ - version 2 matches that accepted for
publication in Phys. Lett.
Microbial Activity Response to Solar Radiation across Contrasting Environmental Conditions in Salar de Huasco, Northern Chilean Altiplano
Indexación: Web of Science; Scopus.In high altitude environments, extreme levels of solar radiation and important differences of ionic concentrations over narrow spatial scales may modulate microbial activity. In Salar de Huasco, a high-altitude wetland in the Andean mountains, the high diversity of microbial communities has been characterized and associated with strong environmental variability. Communities that differed in light history and environmental conditions, such as nutrient concentrations and salinity from different spatial locations, were assessed for bacterial secondary production (BSP, H-3-leucine incorporation) response from short-term exposures to solar radiation. We sampled during austral spring seven stations categorized as: (a) source stations, with recently emerged groundwater (no-previous solar exposure); (b) stream running water stations; (c) stations connected to source waters but far downstream from source points; and (d) isolated ponds disconnected from ground sources or streams with a longer isolation and solar exposure history. Very high values of 0.25 mu E m(-2) s(-1), 72 W m(-2) and 12 W m(-2) were measured for PAR, UVA, and UVB incident solar radiation, respectively. The environmental factors measured formed two groups of stations reflected by principal component analyses (near to groundwater sources and isolated systems) where isolated ponds had the highest BSP and microbial abundance (35 microalgae taxa, picoeukaryotes, nanoflagellates, and bacteria) plus higher salinities and PO43- concentrations. BSP short-term response (4 h) to solar radiation was measured by H-3-leucine incorporation under four different solar conditions: full sun, no UVB, PAR, and dark. Microbial communities established in waters with the longest surface exposure (e.g., isolated ponds) had the lowest BSP response to solar radiation treatments, and thus were likely best adapted to solar radiation exposure contrary to ground source waters. These results support our light history (solar exposure) hypothesis where the more isolated the community is from ground water sources, the better adapted it is to solar radiation. We suggest that factors other than solar radiation (e.g., salinity, PO43-, NO3-) are also important in determining microbial productivity in heterogeneous environments such as the Salar de Huasco.http://journal.frontiersin.org/article/10.3389/fmicb.2016.01857/ful
A to Z of the Muon anomalous magnetic moment in the MSSM with Pati-Salam at the GUT scale
We analyse the low energy predictions of the minimal supersymmetric standard model (MSSM) arising from a GUT scale Pati-Salam gauge group further constrained by an A4 × Z5 family symmetry, resulting in four soft scalar masses at the GUT scale: one left-handed soft mass m0 and three right-handed soft masses m1, m2, m3, one for each generation. We demonstrate that this model, which was initially developed to describe the neutrino sector, can explain collider and non-collider measurements such as the dark matter relic density, the Higgs boson mass and, in particular, the anomalous magnetic moment of the muon (g − 2)μ. Since about two decades, (g − 2)μ suffers a puzzling about 3σ excessoftheexperimentallymeasuredvalueoverthetheoreticalprediction,whichour model is able to fully resolve. As the consequence of this resolution, our model predicts specific regions of the parameter space with the specific properties including light smuons and neutralinos, which could also potentially explain di-lepton excesses observed by CMS and ATLAS
The , , , , and as dynamically generated states from vector meson - vector meson interaction
We report on some recent developments in understanding the nature of the
low-lying mesonic resonances , , ,
, and . In particular we show that these five
resonances can be dynamically generated from vector meson--vector meson
interaction in a coupled-channel unitary approach, which utilizes the
phenomenologically very successful hidden-gauge Lagrangians to produce the
interaction kernel between two vector mesons, which is then unitarized by the
Bethe-Salpeter-equation method. The data on the strong decay branching ratios,
total decay widths, and radiative decay widths of these five states, and on
related decay processes can all be well described by such an approach.
We also make predictions, compare them with the results of earlier studies, and
highlight observables that if measured can be used to distinguish different
pictures of these resonances.Comment: 9 pages; Invited talk at workshop CHIRAL'10, Valencia (Spain), June
21-24, 201
The decay in the molecular picture
From a picture of the X(3872) where the resonance is a bound state of
, we evaluate the decay width into the
channel, which is sensitive to the internal structure of this state.
For this purpose we evaluate the loops through which the X(3872) decays into
its components, and the and the photon are radiated from these
components. We use the local hidden gauge approach extrapolated to SU(4) with a
particular SU(4) breaking. The radiative decay involves anomalous couplings and
we obtain acceptable values which are compared to experiments and results of
other calculations.
Simultaneusly, we evaluate the decay rate for the X(3872) into and , and the results obtained for the ratio of these
decay widths are compatible with the experiment.
We also show the grossly unacceptable results that come from taking only the
component.Comment: 17 pages, 2 figure
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