Bumpy power spectra and  T/T

Abstract

With the recent publication of the measurements of the radiation angular power spectrum from the BOOMERanG‐98 Antarctic flight, it has become apparent that the currently favoured spatially flat cold dark matter model (matter density parameter Ωm=0.3, flatness being restored by a cosmological constant ΩΛ=0.7, Hubble parameter h=0.65, baryon density parameter Ωbh2=0.02) no longer provides a good fit to the data. We describe a phenomenological approach to resurrecting this paradigm. We consider a primordial power spectrum which incorporates a bump, arbitrarily placed at kb and characterized by a Gaussian in log k of standard deviation σb and amplitude Ab, which is superimposed on to a scale‐invariant power spectrum. We generate a range of theoretical models that include a bump at scales consistent with cosmic microwave background (CMB) and large‐scale structure observations, and perform a simple χ2 test to compare our models with the COBE Differential Microwave Radiometer (DMR) data and the recently published BOOMERanG‐98 and MAXIMA‐1 data. Unlike models that include a high baryon content, our models predict a low third acoustic peak. We find that low ℓ observations (20<ℓ<200) are a critical discriminant of the bumps because the transfer function has a sharp cut‐off on the high ℓ side of the first acoustic peak. Current galaxy redshift survey data suggest that excess power is required at a scale around 100 Mpc, corresponding to kb∼0.05 h Mpc−1. For the concordance model, use of a bump‐like feature to account for this excess is not consistent with the constraints imposed by recent CMB data. We note that models with an appropriately chosen break in the power spectrum provide an alternative model that can give distortions similar to those reported in the automated plate measurement (APM) survey as well as consistency with the CMB data. We prefer, however, to discount the APM data in favour of the less biased decorrelated linear power spectrum recently constructed from the Point Source Catalogue Redshift (PSCz) redshift survey. We show that the concordance cosmology can be resurrected using our phenomenological approach and that our best‐fitting model is in agreement with the PSCz observations.

Single field inflation and non-Gaussianity

“…To make the connection with the literature, note that we are not taking a 0 = 1 today. Rather, a 0 = 2ℓ H ≈ 6000 h −1 Mpc which implies that a preferred scale located at 0.004 h Mpc −1 [32] corresponds to a comoving k b = 24 in our case, while a preferred scale located at 0.052 h Mpc −1 [27] yields k b = 312 in our units. In order to illustrate the different forms of the initial spectrum, the functionh(k) is represented in Fig.…”

“…Using the CMBFAST code it was found [29] that this spike in the spectrum is seen at a ≥ 25 per cent smaller wavenumber than the second acoustic peak, while higher values of the baryon contribution Ω b may be needed to fit the amplitude of this feature. If we interpret this feature as originating from the primordial spectrum then, in order to be consistent with observations, the preferred scale k b must lie way below the horizon today, possibly at a scale corresponding to the turn of the power spectrum [27] or at the scale matching the first acoustic peak of the CMB temperature anisotropies [32]. One then sees that the presently available data already restricts the parameter space for the quantities k b and n [33].…”

“…The argument of the hyperbolic tangent is expressed in terms of the logarithm of the wave-number in order to guarantee that k ∈ [0, +∞[, see, e.g., Ref. [32]. A and B are two coefficients that we are going to fix now.…”

Features in the dark energy equation of state and modulations in the Hubble diagram

“…Such features have been invoked to explain the previously observed feature at k ∼ 0.05 Mpc −1 [36,37,38,39], or even to solve the small scale problem of the CDM model [40] 1 . Moreover Ref.…”

Untitled

“…A similar matter spectrum was studied in Barriga et al (2001), which resulted from another kind of inÑationary model with a fast phase transition during inÑation. In contrast, Griffiths, Silk, & Zaroubi (2001) and, most recently, Hannestad, Hansen, & Villante (2000) advocated the existence of a bump in the matter spectrum on signiÐcantly larger scales (k B 0.004 h Mpc~1) based on purely phenomenological grounds. Einasto (2000) analyzed the CMB spectrum resulting from a matter power spectrum with a bump at k \ 0.05 h Mpc~1 as suggested by Chung et al (2000).…”