98 research outputs found

    Generically large nongaussianity in small multifield inflation

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    If forthcoming measurements of cosmic photon polarization restrict the primordial tensor-to-scalar ratio to r<0.01r < 0.01, small field inflation will be a principal candidate for the origin of the universe. Here we show that small multifield inflation, without the hybrid mechanism, typically results in large squeezed nongaussianity. Small multifield potentials contain multiple flat field directions, often identified with the gauge invariant field directions in supersymmetric potentials. We find that unless these field directions have equal slopes, large nongaussianity arises. After identifying relevant differences between large and small two-field potentials, we demonstrate that the latter naturally fulfill the Byrnes-Choi-Hall large nongaussianity conditions. Computations of the primordial power spectrum, spectral index, and squeezed bispectrum, reveal that small two-field models which otherwise match observed primordial perturbations, produce excludably large nongaussianity if the inflatons' field directions have unequal slopes.Comment: 19 pages, 3 figures, factor of 2 corrected in section 3A (thanks to C. Byrnes

    Dark matter ignition of type Ia supernovae

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    Recent studies of low redshift type Ia supernovae (SNIa) indicate that half explode from less than Chandrasekhar mass white dwarfs, implying ignition must proceed from something besides the canonical criticality of Chandrasekhar mass SNIa progenitors. We show that 1βˆ’1001-100 PeV mass asymmetric dark matter, with imminently detectable nucleon scattering interactions, can accumulate to the point of self-gravitation in a white dwarf and collapse, shedding gravitational potential energy by scattering off nuclei, thereby heating the white dwarf and igniting the flame front that precedes SNIa. We combine data on SNIa masses with data on the ages of SNIa-adjacent stars. This combination reveals a 2.8Οƒ2.8 \sigma inverse correlation between SNIa masses and ignition ages, which could result from increased capture of dark matter in 1.4 versus 1.1 solar mass white dwarfs. Future studies of SNIa in galactic centers will provide additional tests of dark-matter-induced type Ia ignition. Remarkably, both bosonic and fermionic SNIa-igniting dark matter also resolve the missing pulsar problem by forming black holes in ≳10\gtrsim 10 Myr old pulsars at the center of the Milky Way.Comment: 6 pages, 2 figures, PRL version considers hotter, denser white dwarfs, references adde

    Beyond the Hubble scale: Super cosmic variance and nongaussianity as a portal to the superhorizon

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    If cosmological perturbations in our Hubble sized volume are nongaussian, then they will be coupled to any larger perturbation modes outside our Hubble volume. This has important consequences for modeling inflation: the scalar power spectrum and spectral index measured in our Hubble volume would depend on an adjacent background of super Hubble perturbations. In other words, a detection of nongaussianity implies a possible portal to the superhorizon. By the same token, ruling out nongaussianity would rule out the possibility that the power spectrum's size and running are accidents of super cosmic variance. In this note, we provide a compact derivation of super cosmic variance, survey recent results, and show how experimental limits on nongaussianity help to rule it out.Comment: 6 pages, 4 figures, to appear in the proceedings of The 10th International Symposium on Cosmology and Particle Astrophysics (CosPA2013

    On the R-Process Enrichment of Dwarf Spheroidal Galaxies

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    Recent observations of Reticulum II have uncovered an overabundance of r-process elements, compared to similar ultra-faint dwarf spheroidal galaxies (UFDs). Because the metallicity and star formation history of Reticulum II appear consistent with all known UFDs, the high r-process abundance of Reticulum II suggests enrichment through a single, rare event, such as a double neutron star (NS) merger. However, we note that this scenario is extremely unlikely, as binary stellar evolution models require significant supernova natal kicks to produce NS-NS or NS-black hole mergers, and these kicks would efficiently remove compact binary systems from the weak gravitational potentials of UFDs. We examine alternative mechanisms for the production of r-process elements in UFDs, including a novel mechanism wherein NSs in regions of high dark matter density implode after accumulating a black-hole-forming mass of dark matter. We find that r-process proto-material ejection by tidal forces, when a single neutron star implodes into a black hole, can occur at a rate matching the r-process abundance of both Reticulum II and the Milky Way. Remarkably, dark matter models which collapse a single neutron star in observed UFDs also solve the missing pulsar problem in the Milky Way Galactic center. We propose tests specific to dark matter r-process production which may uncover, or rule out, this model.Comment: 6 pages, 2 figures, published versio

    Higgs portals to pulsar collapse

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    Pulsars apparently missing from the galactic center could have been destroyed by asymmetric fermionic dark matter (mX=1βˆ’100m_X = 1-100 GeV) coupled to a light scalar (mΟ•=5βˆ’20m_{\phi}= 5-20 MeV), which mixes with the Higgs boson. We point out that this pulsar-collapsing dark sector can resolve the core-cusp problem and will either be excluded or discovered by upcoming direct detection experiments. Another implication is a maximum pulsar age curve that increases with distance from the galactic center, with a normalization that depends on the couplings and masses of dark sector particles. In addition, we use old pulsars outside the galactic center to place bounds on asymmetric Higgs portal models.Comment: 12 pages, 3 figure

    Detecting Dark Matter with Imploding Pulsars in the Galactic Center

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    The paucity of old millisecond pulsars observed at the galactic center of the Milky Way could be the result of dark matter accumulating in and destroying neutron stars. In regions of high dark matter density, dark matter clumped in a pulsar can exceed the Schwarzschild limit and collapse into a natal black hole which destroys the pulsar. We examine what dark matter models are consistent with this hypothesis and find regions of parameter space where dark matter accumulation can significantly degrade the neutron star population within the galactic center while remaining consistent with observations of old millisecond pulsars in globular clusters and near the solar position. We identify what dark matter couplings and masses might cause a young pulsar at the galactic center to unexpectedly extinguish. Finally, we find that pulsar collapse age scales inversely with the dark matter density and linearly with the dark matter velocity dispersion. This implies that maximum pulsar age is spatially dependent on position within the dark matter halo of the Milky Way. In turn, this pulsar age spatial dependence will be dark matter model dependent.Comment: 5 pages, 3 figures, references added to PRL versio

    Supernovae Sparked By Dark Matter in White Dwarfs

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    It was recently demonstrated that asymmetric dark matter can ignite supernovae by collecting and collapsing inside lone sub-Chandrasekhar mass white dwarfs, and that this may be the cause of Type Ia supernovae. A ball of asymmetric dark matter accumulated inside a white dwarf and collapsing under its own weight, sheds enough gravitational potential energy through scattering with nuclei, to spark the fusion reactions that precede a Type Ia supernova explosion. In this article we elaborate on this mechanism and use it to place new bounds on interactions between nucleons and asymmetric dark matter for masses mX=106βˆ’1016m_{X} = 10^{6}-10^{16} GeV. Interestingly, we find that for dark matter more massive than 101110^{11} GeV, Type Ia supernova ignition can proceed through the Hawking evaporation of a small black hole formed by the collapsed dark matter. We also identify how a cold white dwarf's Coulomb crystal structure substantially suppresses dark matter-nuclear scattering at low momentum transfers, which is crucial for calculating the time it takes dark matter to form a black hole. Higgs and vector portal dark matter models that ignite Type Ia supernovae are explored.Comment: 41 pages, 5 figures, PRD versio

    Proton annihilation at hadron colliders and Kamioka: high-energy versus high-luminosity

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    We examine models and prospects for proton annihilation to dileptons, a process which violates baryon and lepton number each by two. We determine that currently Super-Kamiokande would place the most draconian bound on ppβ†’β„“+β„“+pp \rightarrow \ell^+ \ell^+, ruling out new physics below a scale of ∼1.6\sim 1.6 TeV. We also find present and future hadron collider sensitivity to these processes. While 8 TeV LHC data excludes new physics at a scale below ∼800\sim 800 GeV, the reach of a 14 TeV LHC run is ∼1.8\sim 1.8 TeV, putting it on par with the sensitivity of Super-Kamiokande. On the other hand, a 100 TeV proton-proton collider would be sensitive to proton annihilation at a scale up to 10 TeV, allowing it to far exceed the reach of both Super-Kamiokande and the projected 2 TeV reach of Hyper-Kamiokande. Constraints from neutron star observation and cosmological evolution are not competitive. Therefore, although high-luminosity water Cherenkov experiments currently place the leading bounds on baryon and lepton number violation, next generation high-energy hadron colliders will begin surpassing them in sensitivity to some B/LB/L-violating processes.Comment: 21 pages, 3 figure

    Multiscatter stellar capture of dark matter

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    Dark matter may be discovered through its capture in stars and subsequent annihilation. It is usually assumed that dark matter is captured after a single scattering event in the star, however this assumption breaks down for heavy dark matter, which requires multiple collisions with the star to lose enough kinetic energy to become captured. We analytically compute how multiple scatters alter the capture rate of dark matter and identify the parameter space where the affect is largest. Using these results, we then show how multiscatter capture of dark matter on compact stars can be used to probe heavy (mX>m_X > TeV) dark matter with remarkably small dark matter-nucleon scattering cross-sections. As one example, it is demonstrated how measuring the temperature of old neutron stars in the Milky Way's center provides sensitivity to high mass dark matter with dark matter-nucleon scattering cross-sections smaller than the xenon direct detection neutrino floor.Comment: 20 pages, 4 figures, corrected typos and numerical error in Fig. 2, note adde

    Constraints on Bosonic Dark Matter From Observations of Old Neutron Stars

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    Baryon interactions with bosonic dark matter are constrained by the potential for dark matter-rich neutron stars to collapse into black holes. We consider the effect of dark matter self-interactions and dark matter annihilation on these bounds, and treat the evolution of the black hole after formation. We show that, for non-annihilating dark matter, these bounds extend up to mX∼105βˆ’7m_X \sim 10^{5-7} GeV, depending on the strength of self-interactions. However, these bounds are completely unconstraining for annihilating bosonic dark matter with an annihilation cross-section of ≳10βˆ’38cm3/s \gtrsim 10^{-38} {\rm cm^3 /s}. Dark matter decay does not significantly affect these bounds. We thus show that bosonic dark matter accessible to near-future direct detection experiments must participate in an annihilation or self-interaction process to avoid black hole collapse constraints from very old neutron stars.Comment: 22 pages, 4 figures, some comments adde
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