627 research outputs found
Ultrahigh energy cosmic rays from dark matter annihilation
Annihilation of clumped superheavy dark matter provides an interesting
explanation for the origin of ultrahigh energy cosmic rays.
The predicted anisotropy signal provides a unique signature for this
scenario.Comment: 4 pages, 2 figures, to appear in the proceedings of Dark Matter 2002:
Sources and Detection of Dark Matter and Dark Energy in the Univers
Ultra-High Energy Cosmic Rays: The Annihilation of Super-Heavy Relics
We investigate the possibility that ultra-high energy cosmic rays (UHECRs)
originate from the annihilation of relic superheavy (SH) dark matter in the
Galactic halo. In order to fit the data on UHECRs, a cross section of
is
required if the SH dark matter follows a Navarro--Frenk--White (NFW) density
profile. This would require extremely large- contributions to the
annihilation cross section. An interesting finding of our calculation is that
the annihilation in sub-galactic clumps of dark matter dominates over the
annihilations in the smooth dark matter halo, thus implying much smaller values
of the cross section needed to explain the observed fluxes of UHECRs.Comment: To appear in the proceedings of the TAUP conference, September 8-12,
2001 - Gran Sasso Laboratory, Ital
Superheavy dark matter and ultrahigh energy cosmic rays
The phase of inflationary expansion in the early universe produces superheavy
relics in a mass window between 10^{12} GeV and 10^{14} GeV. Decay or
annihilation of these superheavy relics can explain the observed ultrahigh
energy cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff. We emphasize that
the pattern of cosmic ray arrival directions with energies beyond 20 EeV will
decide between the different proposals for the origin of ultrahigh energy
cosmic rays.Comment: Based on an invited talk given by RD at Theory Canada 1, Vancouver,
June 2-5, 200
Incidence and Kinetics of CMV Infection After T-Cell Depleted and Unmodified Allogeneic Hematopoietic Stem Cell Transplantation: A 10-Year Experience at Memorial Sloan-Kettering Cancer Center
Ultra-high energy cosmic rays from annihilation of superheavy dark matter
We consider the possibility that ultra-high energy cosmic rays originate from
the annihilation of relic superheavy dark-matter particles. We find that a
cross section of ~ 10^{-26}cm^2 (M_X/10^{12}GeV)^{3/2} is required
to account for the observed rate of super-GZK events if the superheavy dark
matter follows a Navarro-Frenk-White density profile. This would require
extremely large-l contributions to the annihilation cross section. We also
calculate the possible signature from annihilation in sub-galactic clumps of
dark matter and find that the signal from sub-clumps dominates and may explain
the observed flux with a much smaller cross section than if the superheavy dark
matter is smoothly distributed. Finally, we discuss the expected anisotropy in
the arrival directions of the cosmic rays, which is a characteristic signature
of this scenario.Comment: 13 pages, 4 figures, to appear in Astropart. Phy
Magnesium isotopic composition of the oceanic mantle and oceanic Mg cycling
© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 206 (2017): 151-165, doi:10.1016/j.gca.2017.02.016.To constrain the Mg isotopic composition of the oceanic mantle, investigate Mg isotope fractionation of abyssal peridotites during seafloor alteration, and assess Mg budget in the oceans, a suite of 32 abyssal peridotite samples from the Gakkel Ridge and Southwest Indian Ridge (SWIR) was, for the first time, selected for high-precision Mg isotope analyses. Although most of these samples are extensively altered, largely by serpentinization and weathering, primary olivine, diopside and enstatite grains are preserved in some samples. Olivine grains from the least altered samples have ÎŽ26Mg varying from â0.30 to â0.12â° (n = 7), whereas enstatite and diopside have ÎŽ26Mg varying from â0.27 to â0.16â° (n = 7), and from â0.23 to â0.09â° (n = 6), respectively. Whole-rock ÎŽ26Mg values range from â0.24 to 0.03â° with an average of â0.12 ± 0.13â° (2SD, n = 32). Strongly serpentinized peridotites have lower average ÎŽ26Mg values (ÎŽ26Mg = â0.19 ± 0.07â°, 2SD, n = 7) than weathering-dominated ones (ÎŽ26Mg = â0.10 ± 0.12â°, 2SD, n = 25). Calculated Mg isotopic compositions of fresh mantle peridotites vary from â0.29 to â0.13â°, beyond the previously reported range of the subcontinental lithospheric mantle (â0.25 ± 0.04â°) and the analytical uncertainty (±0.07â°, 2SD). Our study therefore indicates that the oceanic mantle may have similar but slightly heterogeneous Mg isotopic compositions to that of subcontinental lithospheric mantle. Secondary serpentinization does not fractionate Mg isotopes of abyssal peridotites, whereas low-T weathering and formation of clay can result in the enrichment of heavy Mg isotopes in abyssal peridotites. This study also demonstrates that fluid-rock interaction does not necessarily produce rocks with intermediate Mg isotopic compositions. Magnesium isotopes of the rocks thereafter are dependent on the secondary minerals formed. We also conclude that the release of light Mg isotopes into the ocean during alteration of abyssal peridotites can be an important influx of Mg for the seawater Mg budget. Abyssal peridotites with a heavy Mg isotopic signature can be recycled into the mantle in subduction zones and may thus result in heterogeneous Mg isotopic compositions of the oceanic mantle and heavy Mg isotopic compositions of arc magmas.This study was supported by
grants from the National Science Foundation of China (grants 41473038 and
41503010), China Postdoctoral Science Foundation (2015M570145), National
Science Foundation (EAR-1056713 and EAR-1340160) and project MOST104
-2745-M-002-001-ASP granted to SLC. Partial support for HJBD was provided by the
US National Science Foundation (OCE-1434452)
Perturbative and Nonperturbative Contributions to a Simple Model for Baryogenesis
Single field baryogenesis, a scenario for Dirac leptogenesis sourced by a
time-dependent scalar condensate, is studied. We compare the creation of the
charge asymmetry by the perturbative decay of the condensate with the
nonperturbative decay, a process of particle production commonly known in the
context of inflation as preheating. The nonperturbative channel dominates when
the coupling of the scalar field to leptons is sufficiently large.Comment: 11 pages, 3 figure
Dynamical CP Violation in the Early Universe
Following earlier ideas of Dolgov, we show that the asymmetrical dynamical
evolution of fields in the early Universe provides a new source for CP
violation. This can lead to baryogenesis without any additional CP-violating
interactions. The magnitude of this CP violation is time-dependent. In
particular, it vanishes (or is very small) in the late Universe after the
fields have relaxed (or are in their final approach) to their vacuum values. We
provide an explicit example in which our mechanism is realized.Comment: 9 pages, latex, 1 figure (enclosed). The idea of the previous version
was correct, but there were errors in its implementation. This has now been
corrected -- some text modified, references added. Also, one author has been
adde
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