اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSub-percent constraints on cosmological temperature evolution
43
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The redshift dependence of the cosmic microwave background temperature is one of the key cosmological observables. In the standard cosmological model one has $T(z)=T_0(1+z)$, where $T_0$ is the present-day temperature. Deviations from this behavior would imply the presence of new physics. Here we discuss how the combination of all currently available direct and indirect measurements of $T(z)$ constrains the common phenomenological parametrization $T(z)=T_0(1+z)^{1-beta}$, and obtain the first sub-percent constraint on the $beta$ parameter, specifically $beta=(7.6pm8.0)times10^{-3}$ at the $68.3%$ confidence level.
قيم البحث
اقرأ أيضاً
We report strong cosmological constraints on the Brans-Dicke (BD) theory of gravity using Cosmic Microwave Background data from Planck.We consider two types of models. First, the initial condition of the scalar field is fixed to give the same effecti
ve gravitational strength $G_{eff}$ today as the one measured on the Earth, $G_N$. In this case the BD parameter $omega$ is constrained to $omega > 692$ at the $99%$ confidence level, an order of magnitude improvement over previous constraints.In the second type the initial condition for the scalar is a free parameter leading to a somewhat stronger constraint of $omega > 890$ while $G_{eff}$ is constrained to $0.981 <frac{G_{eff}}{G_N} <1.285$ at the same confidence level. We argue that these constraints have greater validity than for the BD theory and are valid for any Horndeski theory, the most general second-order scalar-tensor theory, which approximates BD on cosmological scales. In this sense, our constraints place strong limits on possible modifications of gravity that might explain cosmic acceleration.
We derive new constraints on the neutron lifetime based on the recent Planck 2015 observations of temperature and polarization anisotropies of the CMB. Under the assumption of standard Big Bang Nucleosynthesis, we show that Planck data constrains the
neutron lifetime to $tau_n=(907 pm 69) , [text{s}]$ at $68 %$ c.l.. Moreover, by including the direct measurements of primordial Helium abundance of Aver et al. (2015) and Izotov et al. (2014), we show that cosmological data provide the stringent constraints $tau_n=(875 pm 19) , [text{s}]$ and $tau_n=(921 pm 11) , [text{s}]$ respectively. The latter appears to be in tension with neutron lifetime value quoted by the Particle Data Group ($tau_n=(880.3 pm 1.1) , [text{s}]$). Future CMB surveys as COrE+, in combination with a weak lensing survey as EUCLID, could constrain the neutron lifetime up to a $sim 6 , [text{s}]$ precision.
We investigate a class of dark energy models in which the equation of state undergoes a rapid transition and for which the Hubble SN Ia diagram is known to be poorly discriminant. Interestingly enough, we find that transitions at high redshift can le
ad to distortion in the correlation function of dark matter at lower redshift. We therefore use a combination of the SN Ia Hubble diagram, Cosmic Microwave Background data and power spectrum from the Sloan Digital Sky Survey Luminous Red Galaxies (SDSS LRG) to constrain the redshift of a possible transition. We find that the fundamental cosmological parameters are well constrained independently of the presence of a transition. Acceptable transitions from an equation of state close to $w = 0$ to a value close to -1 are strongly rejected at redshifts much higher than those for which Large Scale Structure and SN Ia data are available: the transition redshift can be rejected up to a value as high as 10. We conclude that no preference for a transition appears from present-day data.
For a robust interpretation of upcoming observations from PLANCK and LHC experiments it is imperative to understand how the inflationary dynamics of a non-minimally coupled Higgs scalar field with gravity may affect the determination of the inflation
ary observables. We make a full proper analysis of the WMAP7+SN+BAO dataset in the context of the non-minimally coupled Higgs inflation field with gravity. For the central value of the top quark pole mass m_T=171.3 GeV, the fit of the inflation model with non-minimally coupled Higgs scalar field leads to the Higgs boson mass between 143.7 and 167 GeV (95% CL). We show that the inflation driven by a non-minimally coupled scalar field to the Einstein gravity leads to significant constraints on the scalar spectral index and tensor-to-scalar ratio when compared with the similar constraints tensor to from the standard inflation with minimally coupled scalar field. We also show that an accurate reconstruction of the Higgs potential in terms of inflationary observables requires an improved accuracy of other parameters of the Standard Model of particle physics as the top quark mass and the effective QCD coupling constant.
This paper aims to put constraints on the parameters of the Scalar Field Dark Matter (SFDM) model, when dark matter is described by a free real scalar field filling the whole Universe, plus a cosmological constant term. By using a compilation of 51 $
H(z)$ data and 1048 Supernovae data from Panteon, a lower limit for the mass of the scalar field was obtained, $m geq 5.1times 10^{-34} $eV and $H_0=69.5^{+2.0}_{-2.1}text{ km s}^{-1}text{Mpc}^{-1}$. Also, the present dark matter density parameter was obtained as $Omega_phi = 0.230^{+0.033}_{-0.031}$ at $2sigma$ confidence level. The results are in good agreement to standard model of cosmology, showing that SFDM model is viable in describing the dark matter content of the universe.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
