17,925 research outputs found
Icelandic Rivers of Light, by Sergio Díaz Ruiz, Spain
No full textSecond place in the 2021 IAU OAE Astrophotography Contest, category Aurorae (time-lapses)
This video shows how aurorae evolve slowly over timescales of a few minutes. Note the clouds being illuminated from behind in the last two shots. Aurorae are caused by interactions between the charged particles blown out in huge explosions from the Sun and the Earth's magnetic field. The changes over time are caused by huge waves of particles pushing the Earth's magnetic field into strange shapes before it snaps back into place.
Credit: Sergio Díaz Ruiz/IAU OA
Testing MeV dark matter with neutrino detectors
No full textMeV particles have been advocated as dark matter (DM) candidates in different contexts. This hypothesis can be tested indirectly by searching for the standard model (SM) products of DM self-annihilations. As the signal from DM self-annihilations depends on the square of the DM density, we might expect a sizable flux of annihilation products from our galaxy. Neutrinos are the least detectable particles in the SM and a null signal in this channel would allow to set the most conservative bound on the total annihilation cross section. Here, we show that neutrino detectors with good energy resolution and low energy thresholds can not only set bounds on the annihilation cross section but actually test the hypothesis of the possible existence of MeV DM, i.e. test the values of the cross section required to explain the observed DM density. At present, the data in the (positron) energy interval [18-82] MeV of the Super-Kamiokande experiment is already able to put a very stringent bound on the annihilation cross section for masses between similar to 15-130 MeV. Future large experiments, like megaton water-Cerenkov or large scintillator detectors, will improve the present limits and, if MeV DM exists, would be able to detect it
Unifying leptogenesis, dark matter and high-energy neutrinos with right-handed neutrino mixing via Higgs portal
No full textWe 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, NDM with mass MDM, plays the role of cold dark matter (DM) and is produced by the mixing with a source RH neutrino, NS with mass MS, induced by Higgs portal interactions. The same interactions are also responsible for NDM decays. We discuss in detail the constraints coming from DM abundance and stability conditions showing that in the hierarchical case, for MDM MS, there is an allowed window on MDM values necessarily implying a contribution, from DM decays, to the high-energy neutrino flux recently detected by IceCube. We also show how the model can explain the matter-antimatter asymmetry of the Universe via leptogenesis in the quasi-degenerate limit. In this case, the DM mass should be within the range 300 GeV MS < MDM 10 PeV. We discuss the specific properties of this high-energy neutrino flux and show the predicted event spectrum for two exemplary cases. Although DM decays, with a relatively hard spectrum, cannot account for all the IceCube high-energy data, we illustrate how this extra source of high-energy neutrinos could reasonably explain some potential features in the observed spectrum. In this way, this represents a unified scenario for leptogenesis and DM that could be tested during the next years with more high-energy neutrino events
Reconstructing WIMP properties with neutrino detectors
No full textif the dark matter of the Universe is constituted by weakly interacting massive particles (WIMP), they would accumulate in the core of astrophysical objects as the Sun and annihilate into particles of the Standard Model. High-energy neutrinos would be produced in the annihilations, both directly and via the subsequent decay of leptons, quarks and bosons. While Cerenkov neutrino detectors/telescopes can only count the number of neutrinos above some threshold energy, we study how, by exploiting their energy resolution, large magnetized iron calorimeter and, possibly, liquid argon and totally active scintillator detectors, planned for future long baseline neutrino experiments, have the capability of reconstructing the neutrino spectrum and might provide information on the dark matter properties. In particular, for a given value of the WIMP mass, we show that a future iron calorimeter could break the degeneracy between the WIMP-proton cross section and the annihilation branching ratios, present for Cerenkov detectors, and constrain their values with good accuracy
Atmospheric neutrino oscillations, theta (13) and neutrino mass hierarchy
No full textWe derive predictions for the Nadir angle (theta(n)) dependence of the ratio N(mu)/N(e) of the rates of the mu-like and e-like multi-GeV events measured in water-Cerenkov detectors in the case of 3-neutrino oscillations of the atmospheric nu(e) (antinu(e)) and nu(mu) (antinu(mu)), driven by one neutrino mass squared difference, |Delta m2(31)| ~ (2.5 - 3.0) x 10^(-3) eV^2 >> Delta m2(21). This ratio is particularly sensitive to the Earth matter effects in the atmospheric neutrino oscillations, and thus to the values of sin^2(theta(13)) and sin^2(theta(23)), theta(13) and theta(23) being the neutrino mixing angle limited by the CHOOZ and Palo Verde experiments and that responsible for the dominant atmospheric nu(mu) -> nu(tau) (antinu(mu) -> antinu(tau)) oscillations. It is also sensitive to the type of neutrino mass spectrum which can be with normal (Delta m2(31) > 0) or with inverted (Delta m2(31) 0.01, sin^2(theta(23)) > 0.5 and at cos(theta(n)) > 0.4, the Earth matter effects modify substantially the theta(n)-dependence of the ratio N(mu)/N(e) and in a way which cannot be reproduced with sin^2(theta(13)) = 0 and a different value of sin^2(theta(23)). For normal hierarchy the effects can be as large as ~ 25% for cos(theta(n)) ~ (0.5 - 0.8), can reach ~ 35% in the Earth core bin cos(theta(n)) ~ (0.84 - 1.0), and might be observable. They are typically by ~ 10% smaller in the inverted hierarchy case. An observation of the Earth matter effects in the Nadir angle distribution of the ratio N(mu)/N(e) would clearly indicate that sin^2(theta(13)) > 0.01 and sin^2(theta(23)) > 0.50
Sterile neutrinos in light of recent cosmological and oscillation data: a multi-flavor scheme approach
No full textLight sterile neutrinos might mix with the active ones and be copiously produced in the early Universe. In the present paper, a detailed multi-flavor analysis of sterile neutrino production is performed. Making some justified approximations allows us to consider not only neutrino interactions with the primeval medium and neutrino coherence breaking effects, but also oscillation effects arising from the presence of three light (mostly-active) neutrino states mixed with two heavier (mostly-sterile) states. First, we emphasize the underlying physics via an analytical description of sterile neutrino abundances that is valid for cases with small mixing between active and sterile neutrinos. Then, we study in detail the phenomenology of (3+2) sterile neutrino models in light of short-baseline oscillation data, including the LSND and MiniBooNE results. Finally, by using the information provided by this analysis, we obtain the expected sterile neutrino cosmological abundances and then contrast them with the most recet available data from Cosmic Microwave Background and Large Scale Structure observations. We conclude that (3+2) models are significantly more disfavored by the internal inconsistencies between sterile neutrino interpretations of appearance and disappearance short-baseline data themselves, rather than by the used cosmological data.OM is supported by a Ram´on y Cajal contract from the Spanish Government. SPR is supported by the Portuguese FCT through the projects POCI/FP/81919/2007 and CFTP-FCT UNIT 777, which are partially funded through POCTI (FEDER). SPR is also partially supported by the Spanish Grant FPA2005-01678 of the MCT. MS would like to acknowledge support by the Spanish Ministry of Science and Innovation via a CSIC JAE-DOC contract, and use of the computing cluster of the experimental neutrino group at IFIC for this work.Peer reviewe
Dynamics of prestressed concrete railway bridges
Get PDFThesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2001.Includes bibliographical references (leaves 80-81).by Sergio Ruiz Meléndez.M.Eng
An intermediate gamma beta-beam neutrino experiment with long baseline
No full textIn order to address some fundamental questions in neutrino physics a wide, future programme of neutrino oscillation experiments is currently under discussion. Among those, long baseline experiments will play a crucial role in providing information on the value of theta(13), the type of neutrino mass ordering and on the value of the CP-violating phase delta, which enters in 3-neutrino oscillations. Here, we consider a beta-beam setup with an intermediate Lorentz factor gamma = 450 and a baseline of 1050 km. This could be achieved in Europe with a beta-beam sourced at CERN to a detector located at the Boulby mine in the United Kingdom. We consider a neutrino run alone and show that, by exploiting the oscillatory pattern of the signal, a very good sensitivity to CP-violation and the type of hierarchy can be reached. We analyse the physics potential of this setup in detail and study two different exposures (1 x 10(21) and 5 x 10(21) ions-kton-years). In both cases, we find that the type of neutrino mass hierarchy could be determined at 99% CL, for all values of delta, for sin(2) 2 theta(13) > 0.03. In the high-exposure scenario, we find that the value of the CP-violating phase delta could be measured with a 99% CL error of similar to 20 degrees if sin(2) 2 theta(13) > 10(-3), with some sensitivity down to values of sin(2) 2 theta(13) similar or equal to 10(-4). The ability to determine the octant of theta(23) is also studied, and good prospects are found for the high-statistics scenario
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