98 research outputs found
Generically large nongaussianity in small multifield inflation
If forthcoming measurements of cosmic photon polarization restrict the
primordial tensor-to-scalar ratio to , 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
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 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 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 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
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
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
Pulsars apparently missing from the galactic center could have been destroyed
by asymmetric fermionic dark matter ( GeV) coupled to a light
scalar ( 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
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
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 GeV. Interestingly, we find that for dark
matter more massive than 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
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 , ruling out new physics below a scale of
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 GeV, the reach of a 14 TeV LHC run is 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 -violating
processes.Comment: 21 pages, 3 figure
Multiscatter stellar capture of dark matter
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 (
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
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 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 . 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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