Search results for " dar"
showing 10 items of 1907 documents
Unifying leptogenesis, dark matter and high-energy neutrinos with right-handed neutrino mixing via Higgs portal
2016
We revisit a model in which neutrino masses and mixing are described by a two right-handed (RH) neutrino seesaw scenario, implying a strictly hierarchical light neutrino spectrum. A third decoupled RH neutrino, $N_{\rm DM}$ with mass $M_{\rm DM}$, plays the role of cold dark matter (DM) and is produced by the mixing with a source RH neutrino, $N_{\rm S}$ with mass $M_{\rm S}$, induced by Higgs portal interactions. The same interactions are also responsible for $N_{\rm DM}$ decays. We discuss in detail the constraints coming from DM abundance and stability conditions, showing that in the hierarchical case ($M_{\rm DM} \gg M_{\rm S}$) there is an allowed window on $M_{\rm DM}$, which necessar…
Axionic and nonaxionic electrodynamics in plane and circular geometry
2023
Various aspects of axion electrodynamics in the presence of a homogeneous and isotropic dielectric medium are discussed. 1. We consider first the "antenna-like" property of a planar dielectric surface in axion electrodynamics, elaborating on the treatment given earlier on this topic by Millar {\it et al.} (2017). We calculate the electromagnetic energy transmission coefficient for a dielectric plate, and compare with the conventional expression in ordinary electrodynamics. 2. We consider the situation where the medium exterior to the plate, assumed elastic, is "bent back" and glued together, so that we obtain a circular dielectric string in which the waves can propagate clockwise or counter…
Implications for dark matter direct detection in the presence of LIGO-motivated primordial black holes
2019
We discuss formation of dark matter (DM) mini-halos around primordial black holes (PBHs) and its implication on DM direct detection experiments, including axion searches. Motivated by LIGO observations, we consider $f_{\textrm{DM}} \simeq 0.01$ as the fraction of DM in PBHs with masses $10 M_{\odot} - 70 M_{\odot}$. In this case, we expect the presence of dressed PBHs after Milky Way halo formation with mini-halo masses peaked around $M_{\textrm{halo}} \sim (50-55) M_{\textrm{PBH}}$. We analyze the effect of tidal forces acting on dressed PBHs within the Milky Way galaxy. In the solar neighborhood, the mini-halos are resistant against tidal disruption from the mean-field potential of the ga…
Einstein, Planck and Vera Rubin: Relevant Encounters Between the Cosmological and the Quantum Worlds
2021
In Cosmology and in Fundamental Physics there is a crucial question like: where the elusive substance that we call Dark Matter is hidden in the Universe and what is it made of? that, even after 40 years from the Vera Rubin seminal discovery [1] does not have a proper answer. Actually, the more we have investigated, the more this issue has become strongly entangled with aspects that go beyond the established Quantum Physics, the Standard Model of Elementary particles and the General Relativity and related to processes like the Inflation, the accelerated expansion of the Universe and High Energy Phenomena around compact objects. Even Quantum Gravity and very exotic Dark Matter particle candid…
Planck-scale effects on WIMP dark matter
2014
There exists a widely known conjecture that gravitational effects violate global symmetries. We study the effect of global-symmetry violating higher-dimension operators induced by Planck-scale physics on the properties of WIMP dark matter. Using an effective description, we show that the lifetime of the WIMP dark matter candidate can satisfy cosmological bounds under reasonable assumptions regarding the strength of the dimension-five operators. On the other hand, the indirect WIMP dark matter detection signal is significantly enhanced due to new decay channels.
Limits on the parameters of the equation of state for interacting dark energy
2010
Under the assumption that cold dark matter and dark energy interact with each other through a small coupling term, $Q$, we constrain the parameter space of the equation of state $w$ of those dark energy fields whose variation of the field since last scattering do not exceed Planck's mass. We use three parameterizations of $w$ and two different expressions for $Q$. Our work extends previous ones.
Light sterile neutrino from extra dimensions and four-neutrino solutions to neutrino anomalies
1999
We propose a four-neutrino model which can reconcile the existing data coming from underground experiments in terms of neutrino oscillations, together with the hint from the LSND experiment and a possible neutrino contribution to the hot dark matter of the Universe. It applies the idea that extra compact dimensions, probed only by gravity and possibly gauge-singlet fields, can lower the fundamental scales such as the Planck, string or unification scales. Our fourth light neutrino $\nu_s$ ($s$ for sterile) is identified with the zero mode of the Kaluza-Klein states. To first approximation \nu_sterile combines with the nu_mu in order to form a Dirac neutrino with mass in the eV range leaving …
Dark matter, dark photon and superfluid He-4 from effective field theory
2020
We consider a model of sub-GeV dark matter whose interaction with the Standard Model is mediated by a new vector boson (the dark photon) which couples kinetically to the photon. We describe the possibility of constraining such a model using a superfluid He-4 detector, by means of an effective theory for the description of the superfluid phonon. We find that such a detector could provide bounds that are competitive with other direct detection experiments only for ultralight vector mediator, in agreement with previous studies. As a byproduct we also present, for the first time, the low-energy effective field theory for the interaction between photons and phonons.
Sociālpedagoģiskā darbība homofobijas mazināšanā 10.-12. klasēs.
2022
Par Titas Ļitvinovas diplomdarba tēmu tika izvēlēta “Sociālpedagoģiskā darbība homofobijas mazināšanai 10.-12.klasēs”. Pētījuma mērķis ir raksturot homofobiju un tās izpausmes veidus skolā, kā arī izstrādāt un aprobēt sociālpedagoģisko programmu homofobijas mazināšanā 10.-12.klasēs. Teorētiskajā daļā ir aprakstīts homofobijas vispārējais raksturojums un tās izpausmes, homofobijas vēsturiskais aspekts, homofobija kā vardarbība, atstumtība un diskriminācija un homofobija skolā. Praktiskā daļa sastāv no pētījuma par homofobiju skolā, kā arī tajā ir iekļauta sociālpedagoģiskā darbības programma un tās aprobācija homofobijas mazināšanai vidusskolas klasēs. Sociālpedagoģiskā programma tika izveid…
Māsu darba organizācija hemodinamiski nestabilu pacientu aprūpē intensīvās terapijas nodaļā
2017
Bakalaura darba tēma ir „Māsu darba organizācija hemodinamiski nestabilu pacientu aprūpē intensīvās terapijas nodaļā”. Tēmas aktualitāti nosaka tas, ka intensīvās terapijas nodaļā hemodinamiski nestabilu pacientu aprūpē, laikam mainoties, māsām ir nepieciešamas aizvien lielākas profesionālas zināšanas veicot darba organizāciju. Darba mērķis ir noskaidrot māsu darba organizāciju hemodinamiski nestabilu pacientu aprūpē intensīvās terapijas nodaļā. Uzsākot darbu tiek izvirzīts pētījuma jautājums: „Kāda ir māsu darba organizācija hemodinamiski nestabilu pacientu aprūpē intensīvās terapijas nodaļā?” Bakalaura darbā tiek pielietota kvalitatīvā pētniecības metode. Kā pētniecības instruments tiek i…