154 research outputs found
Relaxion Dark Matter
We highlight a new connection between the Standard Model hierarchy problem
and the dark matter sector. The key piece is the relaxion field, which besides
scanning the Higgs mass and setting the electroweak scale, also constitutes the
observed dark matter abundance of the universe. The relaxation mechanism is
realized during inflation, and the necessary friction is provided by particle
production. Using this framework we show that the relaxion is a
phenomenologically viable dark matter candidate in the keV mass range.Comment: 11 pages, 2 figures, 1 table; v2: extended discussion, parameter
space includes larger masses and higher reheating temperatures than in v1,
matches version accepted by PRD; v3: numerical error corrected, table and
figures updated, conclusions unchange
Dark Matter, Shared Asymmetries, and Galactic Gamma Ray Signals
We introduce a novel dark matter scenario where the visible sector and the
dark sector share a common asymmetry. The two sectors are connected through an
unstable mediator with baryon number one, allowing the standard model baryon
asymmetry to be shared with dark matter via semi-annihilation. The present-day
abundance of dark matter is then set by thermal freeze-out of this
semi-annihilation process, yielding an asymmetric version of the WIMP miracle
as well as promising signals for indirect detection experiments. As a proof of
concept, we find a viable region of parameter space consistent with the
observed Fermi excess of GeV gamma rays from the galactic center.Comment: 20+12 pages, 11 figures, 1 table; v2: references added, minor
corrections to CMB bounds; v3: footnotes added for clarification, updated
appendix A, conclusions unchanged, version to appear in JCA
Dark Matter Constraints on Composite Higgs Models
In composite Higgs models the pseudo-Nambu-Goldstone Boson (pNGB) nature of
the Higgs field is an interesting alternative for explaning the smallness of
the electroweak scale with respect to the beyond the Standard Model scale. In
non-minimal models additional pNGB states are present and can be a Dark Matter
(DM) candidate, if there is an approximate symmetry suppressing their decay.
Here we assume that the low energy effective theory (for scales much below the
compositeness scale) corresponds to the Standard Model with a pNGB Higgs
doublet and a pNGB DM multiplet. We derive general effective DM Lagrangians for
several possible DM representations (under the SM gauge group), including the
singlet, doublet and triplet cases. Within this framework we discuss how the DM
observables (relic abundance, direct and indirect detection) constrain the
dimension-6 operators induced by the strong sector assuming that DM behaves as
a Weakly Interacting Particle (WIMP) and that the relic abundance is settled
through the freeze-out mechanism. We also apply our general results to two
specific cosets: and , which contain a
singlet and doublet DM candidate, respectively. In particular we show that if
compositeness is a solution to the little hierarchy problem, representations
larger than the triplet are strongly disfavored. Furthermore, we find that
composite models can have viable DM candidates with much smaller direct
detection cross-sections than their non-composite counterparts, making DM
detection much more challenging.Comment: version accepted by JHE
N-Relaxion: Large Field Excursions from a Few Site Relaxion Model
Relaxion models are an interesting new avenue to explain the radiative
stability of the Standard Model scalar sector. They require very large field
excursions, which are difficult to generate in a consistent UV completion and
to reconcile with the compact field space of the relaxion. We propose an N-site
model which naturally generates the large decay constant needed to address
these issues. Our model offers distinct advantages with respect to previous
proposals: the construction involves non-abelian fields, allowing for
controlled high energy behaviour and more model building possibilities, both in
particle physics and inflationary models, and also admits a continuum limit
when the number of sites is large, which may be interpreted as a warped extra
dimension.Comment: 7 pages, 2 figures; v2: version to appear in PR
Higgs relaxation after inflation
We show that the mechanism of cosmological relaxation of the electroweak
scale can take place independently of the inflation mechanism, thus relieving
burdens from the original relaxion proposal. What eventually stops the
(fast-rolling) relaxion field during its cosmological evolution is the
production of particles whose mass is controlled by the Higgs vacuum
expectation value. We first show that Higgs particle production does not work
for that purpose as the Higgs field does not track the minimum of its potential
in the regime where Higgs particles get efficiently produced through their
coupling to the relaxion. We then focus on gauge boson production. We provide a
detailed analysis of the scanning and stopping mechanism and determine the
parameter space for which the relaxion mechanism can take place after
inflation, while being compatible with cosmological constraints, such as the
relaxion dark matter overabundance and Big Bang Nucleosynthesis. We find that
the cutoff scale can be as high as two hundreds of TeV. In this approach, the
relaxion sector is responsible for reheating the visible sector. The stopping
barriers of the periodic potential are large and Higgs-independent,
facilitating model-building. The allowed relaxion mass ranges from 200 MeV up
to the weak scale. In this scenario, the relaxion field excursion is
subplanckian, and is thus many orders of magnitude smaller than in the original
relaxion proposal.Comment: 51 pages, 16 figures. v3: Minor revisions, version published in JHE
Probing optimisation in physics-informed neural networks
A novel comparison is presented of the effect of optimiser choice on the
accuracy of physics-informed neural networks (PINNs). To give insight into why
some optimisers are better, a new approach is proposed that tracks the training
trajectory curvature and can be evaluated on the fly at a low computational
cost. The linear advection equation is studied for several advective
velocities, and we show that the optimiser choice substantially impacts PINNs
model performance and accuracy. Furthermore, using the curvature measure, we
found a negative correlation between the convergence error and the curvature in
the optimiser local reference frame. It is concluded that, in this case, larger
local curvature values result in better solutions. Consequently, optimisation
of PINNs is made more difficult as minima are in highly curved regions.Comment: Accepted at the ICLR 2023 Workshop on Physics for Machine Learnin
Atividades Ligadas ao Programa Nacional de Erradicação da Febre Aftosa.
The supervised curricular internship was conducted at the Agricultural Defense Agency
of Tocantins (ADAPEC), at the Local Veterinary Unit of the municipality of Araguaína.
The stage occurred from August 13 to November 20, 2018, totaling 402 hours under
the supervision of Veterinarian Alessandro José Ferreira dos Santos. During the
internship, several programs were followed, such as the National Program for the
Control and Eradication of Brucellosis and Tuberculosis (PNCEBT), the National
Program for Poultry Health (PNSA), the National Suicide Sanitation Program (PNSS)
and the National Program for Eradication of Foot- ), active surveillance, surveillance
and receipt of vaccines, and dairy supervision. For the effective participation in the
preparation and execution of the second phase of the campaign for the vaccination of
foot-and-mouth disease 2018, the present study discussed the main activities followed
during the internship, with emphasis on the actions carried out during the vaccination
campaign against this disease. It was verified the importance of the actions of the
Defense Agency in PNEFA, so that it could evolve and maintain Tocantins as a FMD free state with vaccination, also demonstrating the preparation of the veterinarians
involved for the next phase with the withdrawal of the vaccine and search to make
Brazil a country free of this disease without vaccination.O estágio curricular supervisionado foi realizado na Agência de Defesa Agropecuária
do Tocantins (ADAPEC), na Unidade Veterinária Local do município de Araguaína. O
estágio ocorreu no período de 13 de agosto a 20 de novembro de 2018, totalizando
402 horas, sob supervisão do Médico Veterinário Alessandro José Ferreira dos
Santos. Durante o estágio foram acompanhados diversos programas como o
Programa Nacional de Controle e Erradicação de Brucelose e Tuberculose (PNCEBT),
Programa Nacional de Sanidade Avícola (PNSA), Programa Nacional de Sanidade
Suídea (PNSS) e Programa Nacional de Erradicação da Febre Aftosa (PNEFA),
vigilâncias ativas, fiscalização e recebimento de vacinas e supervisão em lacticínio.
Pela participação efetiva na preparação e execução da segunda etapa da campanha
de vacinação de febre aftosa 2018, o presente trabalho discorreu sobre as principais
atividades acompanhadas durante o estágio, com ênfase nas ações realizadas
durante a campanha de vacinação contra esta enfermidade. Verificou-se a
importância das ações da Agência de Defesa no PNEFA, para que pudesse evoluir e
manter o Tocantins como estado livre de febre aftosa com vacinação, demonstrando
ainda a preparação dos médicos veterinários envolvidos para a próxima fase com a
retirada da vacina e a busca para fazer do Brasil um país livre desta doença sem
vacinação
Características morfofisiológicas de plantas jovens de Hevea brasiliensis (Willd. Ex Adr de Juss.) Muell. Arg.) submetidas a diferentes ambientes lumínicos e ao estresse hídrico
The rubber tree (Hevea brasiliensis) is Amazonian rainforest tree species. Its bark has laticiferous vessels from which latex are extracted. Currently production overcomes demand, so there is a need for plantation expansion and employment of more efficient management techniques. In order to achieve it, knowing the eco-physiological requirements regarding the availability of resources such as CO 2 , water, nutrients and light can contribute decisively to the global production of rubber plantations. However, it should be noted that climatic changes or even limitations of primary resources during planting almost always impose stressful conditions on plantations, in particular, problems related to the light environment (low or high irradiance) and the availability of water. The aims of this study was investigate morphophysiological and biochemical changes caused on rubber tree seedlings growing under different light intensities and water deficiency as well as analyze their rehydration capacity. The experiments were conducted at Laboratory of Plant Physiology and Biochemistry - INPA. The results showed that the variation of light availability affected the photosynthetic performance of rubber tree seedlings. Plants subjected to low irradiance (47.5 ± 8.2 μmol photon m -2 s -1 ) showed low photosynthetic rates, higher pigment contents, greater leaf area and specific leaf area. On the other hand, under higher irradiation conditions, moderate (257.5 ± 49.3 μmol photon m -2 s -1 ) or high irradiation (642.7 ± 116.9 μmol photon m -2 s -1 ) it was verified higher photosynthetic rates, smaller leaf area and specific leaf area, lower performance indexes, as well as lower values of the quantum photosystem yield. The light capture related results indicate that may have happen photoinhibitory effects over moderate and high irradiance treatments. Although the intermediate irradiance treatment has suffered photoinhibition, it is possible that they were fully reversible, since this treatment had greater biomass accumulation, greater growth in height and higher survival. Farther, it was found that physiological mechanisms were former activated under different light intensities being the morphological ones activated later. So, it is indicated moderate shadowing over this species as soon as it is planted. It was verified that this specie tolerated until 32 days without irrigation, when photosynthesis got close to 0 μmol m -2 s - 1. There was neither alteration on performance index, on photosystem quantum yield, on photosynthetic pigment contents nor on the leaf area. But, an efficient osmotic control must be stressed, probably, influenced by soluble sugar and proline contents. The photosynthesis recovery occurred about 20 days after irrigation be re-established. We conclude that young plants of H.brasiliensis present moderate physiological plasticity in face of different light intensities and water deficiency.A seringueria (Hevea brasiliensis) é uma espécie arbórea, nativa da floresta tropical Amazônica. Sua casca apresenta vasos laticíferos onde se dá a extração de látex. Atualmente, a demanda por látex é maior que a produção, havendo necessidade de expandir e/ou empregar técnicas mais eficientes de manejo dos plantios. Para tanto, conhecer as exigências ecofisiológicas frente à variação na disponibilidade de recursos como CO2, água, nutrientes e luz pode contribuir decisivamente para a produção mundial dos seringais. No entanto, deve-se registrar que as mudanças climáticas ou mesmo limitações dos recursos primários durante o plantio quase sempre impõem condições estressantes ao cultivo, em particular, os problemas relacionados ao ambiente luz (baixa ou alta irradiância) e à disponibilidade de água. O objetivo deste trabalho foi investigar alterações morfofisiológicas e bioquímicas em plantas jovens de H. brasiliensis crescendo sob diferentes ambientes de luz e submetidas à deficiência hídrica, assim como analisar a reidratação. Os experimentos foram conduzidos no Laboratório de Fisiologia e Bioquímica Vegetal – INPA. Os resultados demonstraram que ambientes com diferentes disponibilidades de luz afetam o desempenho fotossintético de plantas jovens de H.brasiliensis. Plantas submetidas à baixa irradiância (47,5 ± 8,2 μmol photon m -2 s -1 ) exibiram menores taxas fotossintéticas, maiores teores de pigmentos, maior área foliar bem como maior área foliar especifica. Por outro lado, sob maiores irradiância, moderada (257,5 ± 49,3 μmol photon m -2 s -1 ) ou alta irradiância (642,7 ± 116,9 μmol photon m -2 s -1 ) apresentaram maiores taxas fotossintéticas, menor área foliar, área foliar especifica e menores índices de desempenho bem como menores valores do rendimento quântico do fotossistema II. Os resultados relacionados à captura de luz sugerem que podem ter ocorrido efeitos fotoinibitórios sob maiores irradiâncias (moderada e alta irradiância). Embora no tratamento intermediário de irradiancia, as plantas tenham sofrido fotoinibição, é possível que tenha sido danos plenamente reversíveis, na medida em que houve maior acúmulo de biomassa, maior crescimento em altura e também maior sobrevivência neste tratamento. Adicionalmente, verificou-se que os primeiros mecanismos acionados sob diferentes intensidades de luz, foram os fisiológicos e depois os morfológicos. Logo, no estabelecimento inicial do cultivo de H. brasiliensis sugere-se que haja sombreamento moderado. Sob deficiência hidrica verificou-se que a espécie tolerou até 32 dias sem irrigação, momento em que a taxa de fotossíntese esteve próximo de 0 μmol m -2 s -1 . Não houve alterações no índice de desempenho, rendimento quântico do fotossistema e nos teores de pigmentos fotossintéticos, assim como na área foliar. Mas, destaca-se eficiente controle osmótico, provavelmente, influenciados pelos teores de açúcar solúvel e de prolina. A recuperação da fotossíntese se deu após 20 dias a partir do retorno da irrigação. Conclui-se que plantas jovens de H. brasiliensis apresentam plasticidade fisiológica moderada frente a diferentes intensidades de luz e sob deficiência hídrica
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