18 research outputs found
Canny Algorithm: A New Estimator for Primordial Non-Gaussianities
We utilize the Canny edge detection algorithm as an estimator for primordial
non-Gaussianities. In preliminary tests on simulated sky patches with a window
size of 57 degrees and multipole moments up to 1024, we find a
distinction between maps with local non-Gaussianity (or
) and Gaussian maps. We present evidence that high resolution CMB
studies will strongly enhance the sensitivity of the Canny algorithm to
non-Gaussianity, making it a promising technique to estimate primordial
non-Gaussianity.Comment: 4 pages, 4 figures; v2. 5pp, as submitted to PRD; v3. 5pp, minor
clarifications and added discussion of negative fNL value
A Signature of Cosmic Strings Wakes in the CMB Polarization
We calculate a signature of cosmic strings in the polarization of the cosmic
microwave background (CMB). We find that ionization in the wakes behind moving
strings gives rise to extra polarization in a set of rectangular patches in the
sky whose length distribution is scale-invariant. The length of an individual
patch is set by the co-moving Hubble radius at the time the string is
perturbing the CMB. The polarization signal is largest for string wakes
produced at the earliest post-recombination time, and for an alignment in which
the photons cross the wake close to the time the wake is created. The maximal
amplitude of the polarization relative to the temperature quadrupole is set by
the overdensity of free electrons inside a wake which depends on the ionization
fraction inside the wake. The signal can be as high as
in degree scale polarization for a string at high redshift (near recombination)
and a string tension given by .Comment: 8 pages, 3 figure
Searching for Signatures of Cosmic Superstrings in the CMB
Because cosmic superstrings generically form junctions and gauge theoretic
strings typically do not, junctions may provide a signature to distinguish
between cosmic superstrings and gauge theoretic cosmic strings. In cosmic
microwave background anisotropy maps, cosmic strings lead to distinctive line
discontinuities. String junctions lead to junctions in these line
discontinuities. In turn, edge detection algorithms such as the Canny algorithm
can be used to search for signatures of strings in anisotropy maps. We apply
the Canny algorithm to simulated maps which contain the effects of cosmic
strings with and without string junctions. The Canny algorithm produces edge
maps. To distinguish between edge maps from string simulations with and without
junctions, we examine the density distribution of edges and pixels crossed by
edges. We find that in string simulations without Gaussian noise (such as
produced by the dominant inflationary fluctuations) our analysis of the output
data from the Canny algorithm can clearly distinguish between simulations with
and without string junctions. In the presence of Gaussian noise at the level
expected from the current bounds on the contribution of cosmic strings to the
total power spectrum of density fluctuations, the distinction between models
with and without junctions is more difficult. However, by carefully analyzing
the data the models can still be differentiated.Comment: 15 page
Interaction Rates in String Gas Cosmology
We study string interaction rates in the Brandenberger-Vafa scenario, the
very early universe cosmology of a gas of strings. This cosmology starts with
the assumption that all spatial dimensions are compact and initially have
string scale radii; some dimensions grow due to some thermal or quantum
fluctuation which acts as an initial expansion velocity. Based on simple
arguments from the low energy equations of motion and string thermodynamics, we
demonstrate that the interaction rates of strings are negligible, so the common
assumption of thermal equilibrium cannot apply. We also present a new analysis
of the cosmological evolution of strings on compact manifolds of large radius.
Then we discuss modifications that should be considered to the usual
Brandenberger-Vafa scenario. To confirm our simple arguments, we give a
numerical calculation of the annihilation rate of winding strings. In
calculating the rate, we also show that the quantum mechanics of strings in
small spaces is important.Comment: 28pp, 3 figures, RevTeX
The 21 cm Signature of Cosmic String Wakes
We discuss the signature of a cosmic string wake in 21cm redshift surveys.
Since 21cm surveys probe higher redshifts than optical large-scale structure
surveys, the signatures of cosmic strings are more manifest in 21cm maps than
they are in optical galaxy surveys. We find that, provided the tension of the
cosmic string exceeds a critical value (which depends on both the redshift when
the string wake is created and the redshift of observation), a cosmic string
wake will generate an emission signal with a brightness temperature which
approaches a limiting value which at a redshift of is close to 400
mK in the limit of large string tension. The signal will have a specific
signature in position space: the excess 21cm radiation will be confined to a
wedge-shaped region whose tip corresponds to the position of the string, whose
planar dimensions are set by the planar dimensions of the string wake, and
whose thickness (in redshift direction) depends on the string tension. For
wakes created at , then at a redshift of the
critical value of the string tension is , and
it decreases linearly with redshift (for wakes created at the time of equal
matter and radiation, the critical value is a factor of two lower at the same
redshift). For smaller tensions, cosmic strings lead to an observable
absorption signal with the same wedge geometry.Comment: 11 pages, 4 figures; a couple of comments added in the discussion
sectio
Canny Algorithm, Cosmic Strings and the Cosmic Microwave Background
We describe a new code to search for signatures of cosmic strings in cosmic
microwave anisotropy maps. The code implements the Canny Algorithm, an edge
detection algorithm designed to search for the lines of large gradients in
maps. Such a gradient signature which is coherent in position space is produced
by cosmic strings via the Kaiser-Stebbins effect. We test the power of our new
code to set limits on the tension of the cosmic strings by analyzing simulated
data with and without cosmic strings. We compare maps with a pure Gaussian
scale-invariant power spectrum with maps which have a contribution of a
distribution of cosmic strings obeying a scaling solution. The maps have
angular scale and angular resolution comparable to what current and future
ground-based small-scale cosmic microwave anisotropy experiments will achieve.
We present tests of the codes, indicate the limits on the string tension which
could be set with the current code, and describe various ways to refine the
analysis. Our results indicate that when applied to the data of ongoing cosmic
microwave experiments such as the South Pole Telescope project, the sensitivity
of our method to the presence of cosmic strings will be more than an order of
magnitude better than the limits from existing analyses.Comment: 19 pp, 14 figures; v4. minor corrections, as appears in journa
Warped Kaluza-Klein Dark Matter
Warped compactifications of type IIB string theory contain natural dark
matter candidates: Kaluza-Klein modes along approximate isometry directions of
long warped throats. These isometries are broken by the full compactification,
including moduli stabilization; we present a thorough survey of Kaluza-Klein
mode decay rates into light supergravity modes and Standard Model particles. We
find that these dark matter candidates typically have lifetimes longer than the
age of the universe. Interestingly, some choices for embedding the Standard
Model in the compactification lead to decay rates large enough to be observed,
so this dark matter sector may provide constraints on the parameter space of
the compactification.Comment: 37pp; v2. references, minor clarificatio
Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK.
BACKGROUND: A safe and efficacious vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), if deployed with high coverage, could contribute to the control of the COVID-19 pandemic. We evaluated the safety and efficacy of the ChAdOx1 nCoV-19 vaccine in a pooled interim analysis of four trials. METHODS: This analysis includes data from four ongoing blinded, randomised, controlled trials done across the UK, Brazil, and South Africa. Participants aged 18 years and older were randomly assigned (1:1) to ChAdOx1 nCoV-19 vaccine or control (meningococcal group A, C, W, and Y conjugate vaccine or saline). Participants in the ChAdOx1 nCoV-19 group received two doses containing 5 × 1010 viral particles (standard dose; SD/SD cohort); a subset in the UK trial received a half dose as their first dose (low dose) and a standard dose as their second dose (LD/SD cohort). The primary efficacy analysis included symptomatic COVID-19 in seronegative participants with a nucleic acid amplification test-positive swab more than 14 days after a second dose of vaccine. Participants were analysed according to treatment received, with data cutoff on Nov 4, 2020. Vaccine efficacy was calculated as 1 - relative risk derived from a robust Poisson regression model adjusted for age. Studies are registered at ISRCTN89951424 and ClinicalTrials.gov, NCT04324606, NCT04400838, and NCT04444674. FINDINGS: Between April 23 and Nov 4, 2020, 23 848 participants were enrolled and 11 636 participants (7548 in the UK, 4088 in Brazil) were included in the interim primary efficacy analysis. In participants who received two standard doses, vaccine efficacy was 62·1% (95% CI 41·0-75·7; 27 [0·6%] of 4440 in the ChAdOx1 nCoV-19 group vs71 [1·6%] of 4455 in the control group) and in participants who received a low dose followed by a standard dose, efficacy was 90·0% (67·4-97·0; three [0·2%] of 1367 vs 30 [2·2%] of 1374; pinteraction=0·010). Overall vaccine efficacy across both groups was 70·4% (95·8% CI 54·8-80·6; 30 [0·5%] of 5807 vs 101 [1·7%] of 5829). From 21 days after the first dose, there were ten cases hospitalised for COVID-19, all in the control arm; two were classified as severe COVID-19, including one death. There were 74 341 person-months of safety follow-up (median 3·4 months, IQR 1·3-4·8): 175 severe adverse events occurred in 168 participants, 84 events in the ChAdOx1 nCoV-19 group and 91 in the control group. Three events were classified as possibly related to a vaccine: one in the ChAdOx1 nCoV-19 group, one in the control group, and one in a participant who remains masked to group allocation. INTERPRETATION: ChAdOx1 nCoV-19 has an acceptable safety profile and has been found to be efficacious against symptomatic COVID-19 in this interim analysis of ongoing clinical trials. FUNDING: UK Research and Innovation, National Institutes for Health Research (NIHR), Coalition for Epidemic Preparedness Innovations, Bill & Melinda Gates Foundation, Lemann Foundation, Rede D'Or, Brava and Telles Foundation, NIHR Oxford Biomedical Research Centre, Thames Valley and South Midland's NIHR Clinical Research Network, and AstraZeneca