اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe CMB flexes its BICEPs while walking the Planck
100
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Recent microwave polarization measurements from the BICEP2 experiment may reveal a long-sought signature of inflation. However, these new results appear inconsistent with the best-fit model from the Planck satellite. We suggest a particularly simple idea for reconciling these data-sets, and for explaining a wide range of phenomena on the cosmic microwave sky.
قيم البحث
اقرأ أيضاً
The recent BICEP2 detection of, what is claimed to be primordial $B$-modes, opens up the possibility of constraining not only the energy scale of inflation but also the detailed acceleration history that occurred during inflation. In turn this can be
used to determine the shape of the inflaton potential $V(phi)$ for the first time - if a single, scalar inflaton is assumed to be driving the acceleration. We carry out a Monte Carlo exploration of inflationary trajectories given the current data. Using this method we obtain a posterior distribution of possible acceleration profiles $epsilon(N)$ as a function of $e$-fold $N$ and derived posterior distributions of the primordial power spectrum $P(k)$ and potential $V(phi)$. We find that the BICEP2 result, in combination with Planck measurements of total intensity Cosmic Microwave Background (CMB) anisotropies, induces a significant feature in the scalar primordial spectrum at scales $ksim 10^{-3}$ Mpc$^{-1}$. This is in agreement with a previous detection of a suppression in the scalar power.
The simplest interpretation of the Bicep2 result is that the scalar primordial power spectrum is slightly suppressed at large scales. These models result in a large tensor-to-scalar ratio $r$. In this work we show that the type of inflationary trajec
tory favoured by Bicep2 also leads to a larger non-Gaussian signal at large scales, roughly an order of magnitude larger than a standard slow-roll trajectory.
Several unexpected features have been observed in the microwave sky at large angular scales, both by WMAP an by Planck. Among those features is a lack of both variance and correlation on the largest angular scales, alignment of the lowest multipole m
oments with one another and with the motion and geometry of the Solar System, a hemispherical power asymmetry or dipolar power modulation, a preference for odd parity modes and an unexpectedly large cold spot in the Southern hemisphere. The individual p-values of the significance of these features are in the per mille to per cent level, when compared to the expectations of the best-fit inflationary $Lambda$CDM model. Some pairs of those features are demonstrably uncorrelated, increasing their combined statistical significance and indicating a significant detection of CMB features at angular scales larger than a few degrees on top of the standard model. Despite numerous detailed investigations, we still lack a clear understanding of these large-scale features, which seem to imply a violation of statistical isotropy and scale invariance of inflationary perturbations. In this contribution we present a critical analysis of our current understanding and discuss several ideas of how to make further progress.
We examine the internal consistency of the Planck 2015 cosmic microwave background (CMB) temperature anisotropy power spectrum. We show that tension exists between cosmological constant cold dark matter (LCDM) model parameters inferred from multipole
s l<1000 (roughly those accessible to Wilkinson Microwave Anisotropy Probe), and from l>=1000, particularly the CDM density, Omega_ch^2, which is discrepant at 2.5 sigma for a Planck-motivated prior on the optical depth, tau=0.07+/-0.02. We find some parameter tensions to be larger than previously reported because of inaccuracy in the code used by the Planck Collaboration to generate model spectra. The Planck l>=1000 constraints are also in tension with low-redshift data sets, including Plancks own measurement of the CMB lensing power spectrum (2.4 sigma), and the most precise baryon acoustic oscillation (BAO) scale determination (2.5 sigma). The Hubble constant predicted by Planck from l>=1000, H_0=64.1+/-1.7 km/s/Mpc, disagrees with the most precise local distance ladder measurement of 73.0+/-2.4 km/s/Mpc at the 3.0 sigma level, while the Planck value from l<1000, 69.7+/-1.7 km/s/Mpc, is consistent within 1 sigma. A discrepancy between the Planck and South Pole Telescope (SPT) high-multipole CMB spectra disfavors interpreting these tensions as evidence for new physics. We conclude that the parameters from the Planck high-multipole spectrum probably differ from the underlying values due to either an unlikely statistical fluctuation or unaccounted-for systematics persisting in the Planck data.
Parity-violating extensions of standard electromagnetism produce cosmic birefringence, the in vacuo rotation of the linear polarisation direction of a photon during propagation. We employ {it Planck} 2018 CMB polarised data to constrain anisotropic b
irefringence, modeled by its angular power spectrum $C_{ell}^{alpha alpha}$, and the cross-correlation with CMB temperature maps, $C_{ell}^{alpha T}$, at scales larger than $sim$15 degrees. We present joint limits on the scale invariant quantity, $A^{alpha alpha} equiv ell (ell +1) , C_{ell}^{alpha alpha} / 2 pi$, and on the analogous amplitude for the cross-correlation, $A^{alpha T} equiv ell (ell +1) , C_{ell}^{alpha T} / 2 pi$. We find no evidence of birefringence within the error budget and obtain $A^{alpha alpha} < 0.104 , mbox{[deg$^2$]}$ and $A^{alpha T}=1.50^{+2.41}_{-4.10} , mbox{[$mu$K$cdot$deg] both at } 95 % mbox{ C.L.}$. The latter bound appears competitive in constraining a few early dark energy models recently proposed to alleviate the $H_{0}$ tension. Slicing the joint likelihood at $A^{alpha T}=0$, the bound on $A^{alpha alpha}$ becomes tighter at $A^{alpha alpha} < 0.085 , mbox{[deg$^2$]}$ at 95$% mbox{ C.L.}$. In addition we recast the constraints on $A^{alpha alpha}$ as a bound on the amplitude of primordial magnetic fields responsible for Faraday rotation, finding $B_{1 {tiny mbox{Mpc}}} < 26.9$ nG and $B_{1 {tiny mbox{Mpc}}} < 24.3$ nG at 95$%$ C.L. for the marginalised and sliced case respectively.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
