542 research outputs found
Constraints on CPT violation from WMAP three year polarization data: a wavelet analysis
We perform a wavelet analysis of the temperature and polarization maps of the
Cosmic Microwave Background (CMB) delivered by the WMAP experiment in search
for a parity violating signal. Such a signal could be seeded by new physics
beyond the standard model, for which the Lorentz and CPT symmetries may not
hold. Under these circumstances, the linear polarization direction of a CMB
photon may get rotated during its cosmological journey, a phenomenon also
called cosmological birefringence. Recently, Feng et al. have analyzed a subset
the WMAP and BOOMERanG 2003 angular power spectra of the CMB, deriving a
constraint that mildly favors a non zero rotation. By using wavelet transforms
we set a tighter limit on the CMB photon rotation angle \Delta\alpha= -2.5 \pm
3.0 (\Delta\alpha= -2.5 \pm 6.0) at the one (two) \sigma level, consistent with
a null detection.Comment: 7 pages, 4 figures, some modifications to match accepted (PRD)
version, results unchange
Constraints on secret neutrino interactions after Planck
(Abridged) Neutrino interactions beyond the standard model may affect the
cosmological evolution and can be constrained through observations. We consider
the possibility that neutrinos possess secret scalar or pseudoscalar
interactions mediated by the Nambu-Goldstone boson of a still unknown
spontaneously broken global symmetry, as in, e.g. , Majoron models. In
such scenarios, neutrinos still decouple at MeV, but become tightly
coupled again ('recouple') at later stages of the cosmological evolution. We
use available observations of CMB anisotropies, including Planck 2013 and the
joint BICEP2/Planck 2015 data, to derive constraints on the quantity
, parameterizing the neutrino collision rate due to
(pseudo)scalar interactions. We consider both a minimal extension of the
standard CDM model, and scenarios with extra relativistic species or
non-vanishing tensors. We find a typical constraint (95% C.L.), implying an upper limit on the redshift
of neutrino recoupling . In the framework of Majoron models,
the upper limit on roughly translates on a constraint on the Majoron-neutrino coupling constant . In general,
the data show a weak () but intriguing preference for non-zero
values of , with best fits in the range , depending on the particular dataset. This is
more evident when either observations from ACT and SPT are included, or the
possibility of non-vanishing tensor modes is considered. In particular, for the
minimal model CDM + and including the Planck 2013,
ACT and SPT data, we report () at 68% confidence level.Comment: 19 pages, 7 figures, 3 tables. Replaced to match version accepted for
pubblication in JCA
A note on the birefringence angle estimation in CMB data analysis
Parity violating physics beyond the standard model of particle physics
induces a rotation of the linear polarization of photons. This effect, also
known as cosmological birefringence (CB), can be tested with the observations
of the cosmic microwave background (CMB) anisotropies which are linearly
polarized at the level of . In particular CB produces non-null CMB
cross correlations between temperature and B mode-polarization, and between E-
and B-mode polarization. Here we study the properties of the so called
D-estimators, often used to constrain such an effect. After deriving the
framework of both frequentist and Bayesian analysis, we discuss the interplay
between birefringence and weak-lensing, which, albeit parity conserving,
modifies pre-existing TB and EB cross correlation.Comment: 12 pages. Accepted for publication in JCA
Testing chirality of primordial gravitational waves with Planck and future CMB data: no hope from angular power spectra
We use the 2015 Planck likelihood in combination with the Bicep2/Keck
likelihood (BKP and BK14) to constrain the chirality, , of primordial
gravitational waves in a scale-invariant scenario. In this framework, the
parameter enters theory always coupled to the tensor-to-scalar ratio,
, e.g. in combination of the form . Thus, the capability to
detect critically depends on the value of . We find that with present
data set is \textit{de facto}unconstrained. We also provide forecasts
for from future CMB experiments, including COrE+, exploring several
fiducial values of . We find that the current limit on is tight enough
to disfavor a neat detection of . For example, in the unlikely case in
which , the maximal chirality case, i.e. , could
be detected with a significance of at best. We conclude
that the two-point statistics at the basis of CMB likelihood functions is
currently unable to constrain chirality and may only provide weak limits on
in the most optimistic scenarios. Hence, it is crucial to investigate
the use of other observables, e.g. provided by higher order statistics, to
constrain these kind of parity violating theories with the CMB.Comment: 15 pages, 3 figures. Updated to match published versio
Cosmic microwave background constraints on secret interactions among sterile neutrinos
Secret contact interactions among eV sterile neutrinos, mediated by a massive
gauge boson (with ), and characterized by a gauge coupling
, have been proposed as a mean to reconcile cosmological observations and
short-baseline laboratory anomalies. We constrain this scenario using the
latest Planck data on Cosmic Microwave Background anisotropies, and
measurements of baryon acoustic oscillations (BAO). We consistently include the
effect of secret interactions on cosmological perturbations, namely the
increased density and pressure fluctuations in the neutrino fluid, and still
find a severe tension between the secret interaction framework and cosmology.
In fact, taking into account neutrino scattering via secret interactions, we
derive our own mass bound on sterile neutrinos and find (at 95% CL) eV or eV from Planck alone or in combination with BAO,
respectively. These limits confirm the discrepancy with the laboratory
anomalies. Moreover, we constrain, in the limit of contact interaction, the
effective strength to be from Planck
(Planck+BAO). This result, together with the mass bound, strongly disfavours
the region with MeV and relatively large coupling , previously indicated as a possible solution to the small scale dark
matter problem.Comment: 15 pages, 3 figures, 4 table
CMB Polarization Systematics, Cosmological Birefringence and the Gravitational Waves Background
Cosmic Microwave Background experiments must achieve very accurate
calibration of their polarization reference frame to avoid biasing the
cosmological parameters. In particular, a wrong or inaccurate calibration might
mimic the presence of a gravitational wave background, or a signal from
cosmological birefringence, a phenomenon characteristic of several
non-standard, symmetry breaking theories of electrodynamics that allow for
\textit{in vacuo} rotation if the polarization direction of the photon.
Noteworthly, several authors have claimed that the BOOMERanG 2003 (B2K)
published polarized power spectra of the CMB may hint at cosmological
birefringence. Such analyses, however, do not take into account the reported
calibration uncertainties of the BOOMERanG focal plane. We develop a formalism
to include this effect and apply it to the BOOMERanG dataset, finding a
cosmological rotation angle . We also
investigate the expected performances of future space borne experiment, finding
that an overall miscalibration larger then for Planck and
for EPIC, if not properly taken into account, will produce a bias on the
constraints on the cosmological parameters and could misleadingly suggest the
presence of a GW background.Comment: 10 pages, 3 figure
Tickling the CMB damping tail: scrutinizing the tension between the ACT and SPT experiments
The Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) have
recently provided new, very precise measurements of the cosmic microwave
background (CMB) anisotropy damping tail. The values of the cosmological
parameters inferred from these measurements, while broadly consistent with the
expectations of the standard cosmological model, are providing interesting
possible indications for new physics that are definitely worth of
investigation. The ACT results, while compatible with the standard expectation
of three neutrino families, indicate a level of CMB lensing, parametrized by
the lensing amplitude parameter A_L, that is about 70% higher than expected. If
not a systematic, this anomalous lensing amplitude could be produced by
modifications of general relativity or coupled dark energy. Vice-versa, the SPT
experiment, while compatible with a standard level of CMB lensing, prefers an
excess of dark radiation, parametrized by the effective number of relativistic
degrees of freedom N_eff. Here we perform a new analysis of these experiments
allowing simultaneous variations in both these, non-standard, parameters. We
also combine these experiments, for the first time in the literature, with the
recent WMAP9 data, one at a time. Including the Hubble Space Telescope (HST)
prior on the Hubble constant and information from baryon acoustic oscillations
(BAO) surveys provides the following constraints from ACT: N_eff=3.23\pm0.47,
A_L=1.65\pm0.33 at 68% c.l., while for SPT we have N_eff=3.76\pm0.34,
A_L=0.81\pm0.12 at 68% c.l.. In particular, the A_L estimates from the two
experiments, even when a variation in N_eff is allowed, are in tension at more
than 95% c.l..Comment: 7 pages, 7 figures, v.2. some typos and sentences correcte
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