81 research outputs found
BFBrain: Scalar Bounded-From-Below Conditions from Bayesian Active Learning
We present a procedure leveraging Bayesian deep active learning to rapidly
produce highly accurate approximate bounded-from-below conditions for arbitrary
renormalizable scalar potentials, in the form of a neural network which may be
saved and exported for use in arbitrary parameter space scans. We explore the
performance of our procedure on three different scalar potentials with either
highly nontrivial or unknown symbolic bounded-from-below conditions (the
two-Higgs doublet model, the three-Higgs doublet model, and a version of the
Georgi-Machacek model without custodial symmetry). We find that we can produce
fast and highly accurate binary classifiers for all three potentials.
Furthermore, for the potentials for which no known symbolic necessary and
sufficient conditions on boundedness-from-below exist, our classifiers
substantially outperform some common approximate analytical methods, such as
producing tractable sufficient but not necessary conditions or evaluating
boundedness-from-below conditions for scenarios in which only a subset of the
theory's fields achieve vev's. Our methodology can be readily adapted to any
renormalizable scalar field theory. For the community's use, we have developed
a Python package, BFBrain, which allows for the rapid implementation of our
analysis procedure on user-specified scalar potentials with a high degree of
customizability.Comment: 33 pages and 13 figures, plus appendices. BFBrain package available
at https://github.com/Gwojci03/BFBrai
Variant Nelson-Barr Mechanism with Minimal Flavor Violation
Within the general framework of using spontaneous CP violation to solve the
strong CP problem, we construct a variant Nelson-Barr model in which the
Standard Model (SM) quark contribution to the strong CP phase is cancelled by
new heavy QCD-charged fermions. This cancellation is ensured by choosing
conjugate representations for the new colored states under the same global
flavor symmetry of SM quarks. Choosing the global flavor symmetry to be that of
minimal flavor violation, we suppress higher-order corrections to the strong CP
phase to well below current experimental constraints. More than two dozen
massless Goldstone bosons emerge from spontaneous flavor symmetry breaking,
which yield strong astrophysical constraints on the symmetry breaking scale. In
the early universe, the Goldstone bosons can be thermally produced from their
interactions with the heavy colored fermions and contribute to at a measurable level. As a function of reheating temperature, the
predicted shows an interesting plateau behavior we dub the
``flavor stairway", which encodes information about the SM quark flavor
structure.Comment: 20 pages + appendices, 3 figures, v2: References and some discussion
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Ghosts- and Tachyon-Free Regions of the Randall-Sundrum Model Parameter Space
Model building within the Randall-Sundrum (RS) framework generally involves
placing the Standard Model fields in the bulk. Such fields may possess non-zero
values for their associated brane-localized kinetic terms (BLKTs) in addition
to possible bulk mass parameters. In this paper we clearly identify the regions
of the RS model parameter space where the presence of bulk mass terms and BLKTs
yield a setup which is free from both ghost and tachyon instabilities. Such
physically acceptable parameter space regions can then be used to construct
realistic and phenomenologically viable RS models.Comment: Latex, 30 pages, 2 figure
Should the poultry red mite Dermanyssus gallinae be of wider concern for veterinary and medical science?
The poultry red mite Dermanyssus gallinae is best known as a threat to the laying-hen industry; adversely affecting production and hen health and welfare throughout the globe, both directly and through its role as a disease vector. Nevertheless, D. gallinae is being increasingly implemented in dermatological complaints in non-avian hosts, suggesting that its significance may extend beyond poultry. The main objective of the current work was to review the potential of D. gallinae as a wider veterinary and medical threat. Results demonstrated that, as an avian mite, D. gallinae is unsurprisingly an occasional pest of pet birds. However, research also supports that these mites will feed from a range of other animals including: cats, dogs, rodents, rabbits, horses and man. We conclude that although reported cases of D. gallinae infesting mammals are relatively rare, when coupled with the reported genetic plasticity of this species and evidence of permanent infestations on non-avian hosts, potential for host-expansion may exist. The impact of, and mechanisms and risk factors for such expansion are discussed, and suggestions for further work made. Given the potential severity of any level of host-expansion in D. gallinae, we conclude that further research should be urgently conducted to confirm the full extent of the threat posed by D. gallinae to (non-avian) veterinary and medical sectors
Shattered pellet injection experiments at JET in support of the ITER disruption mitigation system design
A series of experiments have been executed at JET to assess the efficacy of the newly installed shattered pellet injection (SPI) system in mitigating the effects of disruptions. Issues, important for the ITER disruption mitigation system, such as thermal load mitigation, avoidance of runaway electron (RE) formation, radiation asymmetries during thermal quench mitigation, electromagnetic load control and RE energy dissipation have been addressed over a large parameter range. The efficiency of the mitigation has been examined for the various SPI injection strategies. The paper summarises the results from these JET SPI experiments and discusses their implications for the ITER disruption mitigation scheme
New H-mode regimes with small ELMs and high thermal confinement in the Joint European Torus
New H-mode regimes with high confinement, low core impurity accumulation, and small edge-localized mode perturbations have been obtained in magnetically confined plasmas at the Joint European Torus tokamak. Such regimes are achieved by means of optimized particle fueling conditions at high input power, current, and magnetic field, which lead to a self-organized state with a strong increase in rotation and ion temperature and a decrease in the edge density. An interplay between core and edge plasma regions leads to reduced turbulence levels and outward impurity convection. These results pave the way to an attractive alternative to the standard plasmas considered for fusion energy generation in a tokamak with a metallic wall environment such as the ones expected in ITER.& nbsp;Published under an exclusive license by AIP Publishing
Overview of JET results for optimising ITER operation
The JET 2019–2020 scientific and technological programme exploited the results of years of concerted scientific and engineering work, including the ITER-like wall (ILW: Be wall and W divertor) installed in 2010, improved diagnostic capabilities now fully available, a major neutral beam injection upgrade providing record power in 2019–2020, and tested the technical and procedural preparation for safe operation with tritium. Research along three complementary axes yielded a wealth of new results. Firstly, the JET plasma programme delivered scenarios suitable for high fusion power and alpha particle (α) physics in the coming D–T campaign (DTE2), with record sustained neutron rates, as well as plasmas for clarifying the impact of isotope mass on plasma core, edge and plasma-wall interactions, and for ITER pre-fusion power operation. The efficacy of the newly installed shattered pellet injector for mitigating disruption forces and runaway electrons was demonstrated. Secondly, research on the consequences of long-term exposure to JET-ILW plasma was completed, with emphasis on wall damage and fuel retention, and with analyses of wall materials and dust particles that will help validate assumptions and codes for design and operation of ITER and DEMO. Thirdly, the nuclear technology programme aiming to deliver maximum technological return from operations in D, T and D–T benefited from the highest D–D neutron yield in years, securing results for validating radiation transport and activation codes, and nuclear data for ITER
The role of ETG modes in JET-ILW pedestals with varying levels of power and fuelling
We present the results of GENE gyrokinetic calculations based on a series of JET-ITER-like-wall (ILW) type I ELMy H-mode discharges operating with similar experimental inputs but at different levels of power and gas fuelling. We show that turbulence due to electron-temperature-gradient (ETGs) modes produces a significant amount of heat flux in four JET-ILW discharges, and, when combined with neoclassical simulations, is able to reproduce the experimental heat flux for the two low gas pulses. The simulations plausibly reproduce the high-gas heat fluxes as well, although power balance analysis is complicated by short ELM cycles. By independently varying the normalised temperature gradients (omega(T)(e)) and normalised density gradients (omega(ne )) around their experimental values, we demonstrate that it is the ratio of these two quantities eta(e) = omega(Te)/omega(ne) that determines the location of the peak in the ETG growth rate and heat flux spectra. The heat flux increases rapidly as eta(e) increases above the experimental point, suggesting that ETGs limit the temperature gradient in these pulses. When quantities are normalised using the minor radius, only increases in omega(Te) produce appreciable increases in the ETG growth rates, as well as the largest increases in turbulent heat flux which follow scalings similar to that of critical balance theory. However, when the heat flux is normalised to the electron gyro-Bohm heat flux using the temperature gradient scale length L-Te, it follows a linear trend in correspondence with previous work by different authors
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