25 research outputs found
Freeze-in at stronger coupling
Predictivity of many non-thermal dark matter (DM) models is marred by the
gravitational production background. This problem is ameliorated in models with
lower reheating temperature , which allows for dilution of gravitationally
produced relics. We study the freeze-in dark matter production mechanism in the
thermal bath with the electroweak scale temperature. The process is
Boltzmann-suppressed if the dark matter mass is above . In this case, the
coupling to the thermal bath has to be significant to account for the observed
dark matter relic density. As a result, the direct DM detection experiments
already probe such freeze-in models, excluding significant parts of parameter
space. The forthcoming experiments will explore this framework further,
extending to lower couplings and higher reheating temperatures.Comment: 10 page
Scalar field dark matter and the Higgs field
We discuss the possibility that dark matter corresponds to an oscillating scalar field coupled to the Higgs boson. We argue that the initial field amplitude should generically be of the order of the Hubble parameter during inflation, as a result of its quasi-de Sitter fluctuations. This implies that such a field may account for the present dark matter abundance for masses in the range 10^-6 - 10^-4 eV, if the tensor-to-scalar ratio is within the range of planned CMB experiments. We show that such mass values can naturally be obtained through either Planck-suppressed non-renormalizable interactions with the Higgs boson or, alternatively, through renormalizable interactions within the Randall–Sundrum scenario, where the dark matter scalar resides in the bulk of the warped extra-dimension and the Higgs is confined to the infrared brane
Testing freeze-in with axial and vector Z′ bosons
The freeze-in production of Feebly Interacting Massive Particle (FIMP) dark matter in the early universe is an appealing alternative to the well-known and constrained Weakly Interacting Massive Particle (WIMP) paradigm. Although challenging, the phenomenology of FIMP dark matter has been receiving growing attention and is possible in a few scenarios. In this work, we contribute to this endeavor by considering a Z′ portal to fermionic dark matter, with the Z′ having both vector and axial couplings and a mass ranging from MeV up to PeV. We evaluate the bounds on both freeze-in and freeze-out from direct detection, atomic parity violation, leptonic anomalous magnetic moments, neutrino-electron scattering, collider, and beam dump experiments. We show that FIMPs can already be tested by most of these experiments in a complementary way, whereas WIMPs are especially viable in the Z′ low mass regime, in addition to the Z′ resonance region. We also discuss the role of the axial couplings of Z′ in our results. We therefore hope to motivate specific realizations of this model in the context of FIMPs, as well as searches for these elusive dark matter candidates
Mercados municipais : estruturas decadentes ou polos de animação
Presentes em praticamente todo o território nacional, os Mercados Municipais são geralmente reconhecidos como estruturas tradicionais de comércio retalhista de proximidade, funcionando como posto de abastecimento das populações. Estes espaços apresentaram também ao longo dos tempos uma vertente socioeconómica, cultural e urbana muito forte, revelando-se como uma mais-valia para a evolução e dinamização dos centros dos aglomerados em que se inserem, sejam eles de cariz urbano ou rural.
Apesar disso, os Mercados Municipais têm perdido algum destaque como lugar de sucesso, se comparado com o que acontecia noutros tempos. Por esse motivo, defende-se que tais estruturas precisam de ser reinterpretadas, preservadas e animadas, sendo esse o caminho a seguir na ótica da Reabilitação Urbana. Só assim se podem manter como relevantes e, desse modo, projetarem-se para o futuro.
A resposta à pergunta base que está na origem deste trabalho (“Mercados Municipais: Estruturas decadentes ou polos de animação?”) começa por uma resenha histórica sobre a origem e evolução do Mercado ao longo dos tempos, debruçando-se depois sobre a caracterização e principais funções de referência dos Mercados Municipais no quotidiano. Uma análise sobre os cenários possíveis de evolução e as hipóteses de desenvolvimento futuro concluem num conjunto de formas possíveis de intervenção de modo a garantir que os Mercados se reinventem e garantam a sua continuidade. E, deste modo, continuarem a ser também polos dinamizadores das comunidades.
Para ilustrar a importância deste equipamento coletivo na vida e identidade da comunidade, é desenvolvido um estudo sobre o Mercado de Febres, localizado no centro da vila de Febres, situado no concelho de Cantanhede
Scale-invariant scalar field dark matter through the Higgs portal
We discuss the dynamics and phenomenology of an oscillating scalar field
coupled to the Higgs boson that accounts for the dark matter in the Universe.
The model assumes an underlying scale invariance such that the scalar field
only acquires mass after the electroweak phase transition, behaving as dark
radiation before the latter takes place. While for a positive coupling to the
Higgs field the dark scalar is stable, for a negative coupling it acquires a
vacuum expectation value after the electroweak phase transition and may decay
into photon pairs, albeit with a mean lifetime much larger than the age of the
Universe. We explore possible astrophysical and laboratory signatures of such a
dark matter candidate in both cases, including annihilation and decay into
photons, Higgs decay, photon-dark scalar oscillations and induced oscillations
of fundamental constants. We find that dark matter within this scenario will be
generically difficult to detect in the near future, except for the promising
case of a 7 keV dark scalar decaying into photons, which naturally explains the
observed galactic and extra-galactic 3.5 keV X-ray line.publishe