479 research outputs found
Impact of polarization on the intrinsic cosmic microwave background bispectrum
We compute the cosmic microwave background (CMB) bispectrum induced by the evolution of the primordial density perturbations, including for the first time both temperature and polarization using a second-order Boltzmann code. We show that including polarization can increase the signal-to-noise by a factor 4 with respect to temperature alone. We find the expected signal-to-noise for this intrinsic bispectrum of S=N ¼ 3.8; 2.9; 1.6 and 0.5 for an ideal experiment with an angular resolution of lmax ¼ 3000, the proposed CMB surveys PRISM and COrE, and Planck’s polarized data, respectively; the bulk of this signal comes from E-mode polarization and from squeezed configurations. We discuss how CMB lensing is expected to reduce these estimates as it suppresses the bispectrum for squeezed configurations and contributes to the noise in the estimator. We find that the presence of the intrinsic bispectrum will bias a measurement of primordial non-Gaussianity of local type by fintr NL ¼ 0.66 for an ideal experiment with lmax ¼ 3000. Finally, we verify the robustness of our results by recovering the analytic approximation for the squeezed-limit bispectrum in the general polarized case
The Intrinsic Matter Bispectrum in CDM
We present a fully relativistic calculation of the matter bispectrum at
second order in cosmological perturbation theory assuming a Gaussian primordial
curvature perturbation. For the first time we perform a full numerical
integration of the bispectrum for both baryons and cold dark matter using the
second-order Einstein-Boltzmann code, SONG. We review previous analytical
results and provide an improved analytic approximation for the second-order
kernel in Poisson gauge which incorporates Newtonian nonlinear evolution,
relativistic initial conditions, the effect of radiation at early times and the
cosmological constant at late times. Our improved kernel provides a percent
level fit to the full numerical result at late times for most configurations,
including both equilateral shapes and the squeezed limit. We show that baryon
acoustic oscillations leave an imprint in the matter bispectrum, making a
significant impact on squeezed shapes.Comment: Accepted for publication in JCAP. 17 pages + appendices, 6 figures.
Code available at GitHub: http://github.com/coccoinomane/son
Non-linear Evolution of Matter Power Spectrum in Modified Theory of Gravity
We present a formalism to calculate the non-linear matter power spectrum in
modified gravity models that explain the late-time acceleration of the Universe
without dark energy. Any successful modified gravity models should contain a
mechanism to recover General Relativity (GR) on small scales in order to avoid
the stringent constrains on deviations from GR at solar system scales. Based on
our formalism, the quasi non-linear power spectrum in the
Dvali-Gabadadze-Porratti (DGP) braneworld models and gravity models are
derived by taking into account the mechanism to recover GR properly. We also
extrapolate our predictions to fully non-linear scales using the Parametrized
Post Friedmann (PPF) framework. In gravity models, the predicted
non-linear power spectrum is shown to reproduce N-body results. We find that
the mechanism to recover GR suppresses the difference between the modified
gravity models and dark energy models with the same expansion history, but the
difference remains large at weakly non-linear regime in these models. Our
formalism is applicable to a wide variety of modified gravity models and it is
ready to use once consistent models for modified gravity are developed.Comment: 25 pages, 8 figures, comparison to N-body simulations in DGP added,
published in PR
Characterising Vainshtein Solutions in Massive Gravity
We study static, spherically symmetric solutions in a recently proposed
ghost-free model of non-linear massive gravity. We focus on a branch of
solutions where the helicity-0 mode can be strongly coupled within certain
radial regions, giving rise to the Vainshtein effect. We truncate the analysis
to scales below the gravitational Compton wavelength, and consider the weak
field limit for the gravitational potentials, while keeping all non-linearities
of the helicity-0 mode. We determine analytically the number and properties of
local solutions which exist asymptotically on large scales, and of local
(inner) solutions which exist on small scales. We find two kinds of asymptotic
solutions, one of which is asymptotically flat, while the other one is not, and
also two types of inner solutions, one of which displays the Vainshtein
mechanism, while the other exhibits a self-shielding behaviour of the
gravitational field. We analyse in detail in which cases the solutions match in
an intermediate region. The asymptotically flat solutions connect only to inner
configurations displaying the Vainshtein mechanism, while the non
asymptotically flat solutions can connect with both kinds of inner solutions.
We show furthermore that there are some regions in the parameter space where
global solutions do not exist, and characterise precisely in which regions of
the phase space the Vainshtein mechanism takes place.Comment: 21 pages, 7 figures, published versio
New Host and Ocean Records for the Parasitic Copepod Bobkabata kabatabobbus (Lernaeosoleidae: Poecilostomatoida)
The parasitic copepod Bobkabata kabatabobbus Hogans & Benz is reported
for the first time from the Pacific Ocean and from the darkfin sculpin,
Malacocottus zonurus (Psychrolutidae: Scorpaeniformes). Based on five specimens,
several morphological features are reported for the first time for B. kabatabobbus,
including a second protuberance on the cephalothorax, a pair of vestigial
legs on the neck, and two dark-staining sclerites on the trunk that may represent
body segment boundaries or interpodal bars
Gravitational backreaction of anti-D branes in the warped compactification
We derive a low-energy effective theory for gravity with anti-D branes, which
are essential to get de Sitter solutions in the type IIB string warped
compactification, by taking account of gravitational backreactions of anti-D
branes. In order to see the effects of the self-gravity of anti-D branes, a
simplified model is studied where a 5-dimensional anti-de Sitter ({\it AdS})
spacetime is realized by the bulk cosmological constant and the 5-form flux,
and anti-D branes are coupled to the 5-form field by Chern-Simon terms. The
{\it AdS} spacetime is truncated by introducing UV and IR cut-off branes like
the Randall-Sundrum model. We derive an effective theory for gravity on the UV
brane and reproduce the familiar result that the tensions of the anti-D branes
give potentials suppressed by the forth-power of the warp factor at the
location of the anti-D branes. However, in this simplified model, the potential
energy never inflates the UV brane, although the anti-D-branes are inflating.
The UV brane is dominated by dark radiation coming from the projection of the
5-dimensional Weyl tensor, unless the moduli fields for the anti-D branes are
stabilized. We comment on the possibility of avoiding this problem in a
realistic string theory compactification.Comment: typos corrected, 11 pages, 3 figure
Testing Higgs models via the vertex by a recoil method at the International Linear Collider
In general, charged Higgs bosons appear in non-minimal Higgs models.
The vertex is known to be related to the violation of the
global symmetry (custodial symmetry) in the Higgs sector. Its magnitude
strongly depends on the structure of the exotic Higgs models which contain
higher isospin representations such as triplet Higgs bosons. We study
the possibility of measuring the vertex via single charged
Higgs boson production associated with the boson at the International
Linear Collider (ILC) by using the recoil method. The feasibility of the signal
is analyzed assuming the polarized
electron and positron beams and the expected detector performance for the
resolution of the two-jet system at the ILC. The background events can be
reduced to a considerable extent by imposing the kinematic cuts even if we take
into account the initial state radiation. For a relatively light charged Higgs
boson whose mass is in the region of 120-130 GeV , the vertex would be precisely testable especially
when the decay of is lepton specific. The exoticness of the extended
Higgs sector can be explored by using combined information for this vertex and
the rho parameter.Comment: 22 pages, 23 figure
Appearance of classical Mixmaster Universe from the No-Boundary Quantum State
We investigate the appearance of the classical anisotropic universe from the
no-boundary quantum state according to the prescription proposed by Hartle,
Hawking and Hertog. Our model is homogeneous, anisotropic, closed universes
with a minimally coupled scalar field and cosmological constant. We found that
there are an ensemble of classical Lorentzian histories with anisotropies and
experience inflationary expansion at late time, and the probability of
histories with anisotropies are lower than isotropic histories. Thus the
no-boundary condition may be able to explain the emergence of our universe. If
the classical late time histories are extended back, some become singular by
the existence of initial anisotropies with large accelerations. However we do
not find any chaotic behavior of anisotropies near the initial singularity.Comment: 14 pages, 14 figure
Probing Cooper Pairs with Franson Interferometry
A setup based on the Franson optical interferometer is analyzed, which allows
us to detect the coherence properties of Cooper pairs emerging via tunneling
from a superconductor in contact with two one-dimensional channels. By tuning
the system parameters we show that both the internal coherence of the emitted
Cooper pairs, which is proportional to Pippard's length, and the de Broglie
wavelength of their center-of-mass motion can be measured via current-current
correlation measurements.Comment: 9 pages, 3 figure
Strong ice-ocean interaction beneath Shirase Glacier Tongue in East Antarctica
Mass loss from the Antarctic ice sheet, Earth’s largest freshwater reservoir, results directly in global sea-level rise and Southern Ocean freshening. Observational and modeling studies have demonstrated that ice shelf basal melting, resulting from the inflow of warm water onto the Antarctic continental shelf, plays a key role in the ice sheet’s mass balance. In recent decades, warm ocean-cryosphere interaction in the Amundsen and Bellingshausen seas has received a great deal of attention. However, except for Totten Ice Shelf, East Antarctic ice shelves typically have cold ice cavities with low basal melt rates. Here we present direct observational evidence of high basal melt rates (7–16 m yr−1) beneath an East Antarctic ice shelf, Shirase Glacier Tongue, driven by southward-flowing warm water guided by a deep continuous trough extending to the continental slope. The strength of the alongshore wind controls the thickness of the inflowing warm water layer and the rate of basal melting
- …