Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Higher neutrino mass allowed if Cold Dark Matter and Dark Energy are coupled

G. La Vacca, S. A. Bonometto, L. P. L. Colombo

TL;DR

The paper investigates whether a coupling between Cold Dark Matter (CDM) and Dark Energy (DE) can relax cosmological neutrino-mass bounds. It adopts a dynamical DE model with a scalar field $\phi$ and a SUGRA-type potential $V(\phi)$, introducing a coupling parameter $\beta$ that transfers energy between CDM and DE, yielding an effective potential $\bar{V}$ that can mimic phantom-like evolution without exotic physics. Using CAMB to compute spectra and a Fisher-matrix framework, the authors map how $\sum m_\nu$ and $\beta$ trade off against CMB and large-scale-structure observables under two experimental scenarios (WMAP+2dF and Planck+SDSS). They find that under W-like data the bound is $\sum m_\nu < \sim 1.05$ eV and $\beta < \sim 0.22$, while Planck+SDSS tightens to $\sum m_\nu < \sim 0.40$ eV and $\beta < \sim 0.07$, indicating substantial potential to ease neutrino-mass limits when CDM-DE coupling is allowed; they also stress the need for MCMC analyses to obtain robust likelihoods.

Abstract

Cosmological limits on neutrino masses are softened, by more than a factor 2, if Cold Dark Matter (CDM) and Dark Energy (DE) are coupled. In turn, a neutrino mass yielding $Ω_ν$ up to $\sim0.20$ allows coupling levels $β\simeq 0.15, $ or more, already easing the coincidence problem. The coupling, in fact, displaces both $P(k)$ and $C_l$ spectra in a fashion opposite to neutrino mass. Estimates are obtained through a Fisher--matrix technique.

Higher neutrino mass allowed if Cold Dark Matter and Dark Energy are coupled

TL;DR

The paper investigates whether a coupling between Cold Dark Matter (CDM) and Dark Energy (DE) can relax cosmological neutrino-mass bounds. It adopts a dynamical DE model with a scalar field and a SUGRA-type potential , introducing a coupling parameter that transfers energy between CDM and DE, yielding an effective potential that can mimic phantom-like evolution without exotic physics. Using CAMB to compute spectra and a Fisher-matrix framework, the authors map how and trade off against CMB and large-scale-structure observables under two experimental scenarios (WMAP+2dF and Planck+SDSS). They find that under W-like data the bound is eV and , while Planck+SDSS tightens to eV and , indicating substantial potential to ease neutrino-mass limits when CDM-DE coupling is allowed; they also stress the need for MCMC analyses to obtain robust likelihoods.

Abstract

Cosmological limits on neutrino masses are softened, by more than a factor 2, if Cold Dark Matter (CDM) and Dark Energy (DE) are coupled. In turn, a neutrino mass yielding up to allows coupling levels or more, already easing the coincidence problem. The coupling, in fact, displaces both and spectra in a fashion opposite to neutrino mass. Estimates are obtained through a Fisher--matrix technique.

Paper Structure

This paper contains 8 sections, 31 equations, 9 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Coupled--DE models
  3. Some angular and linear spectra
  4. Fisher matrix (data and technique)
  5. Fisher matrix (results)
  6. Exploring the parameter space
  7. Conclusions
  8. Fluctuation evolution in models with dynamical and coupled DE

Figures (9)

  • Figure 1: Transfer functions in cosmologies with/without coupling and with/without 2 massive neutrinos. Coupling and mass are selected so to yield an approximate balance. The functions are multiplied by $k^{1.5}$, to help the reader to distinguish different cases.
  • Figure 2: Angular anisotropy spectra for the same models of the previous figure. Due to intrinsic $C_l$ oscillations, this Figure is slightly harder to read. In the lower frame we also give the spectral differences between 00-- and CM--models. Large $l$ oscillations could be further damped by a shift by 1 or 2 units along $l$. The dotted lines represent the cosmic variance interval.
  • Figure 3: 1-- and 2--$\sigma$ confidence levels for a 2--massive--neutrino model, assuming that the true cosmology is a SUGRA model with $\log(\Lambda/{\rm GeV})=1.1$, while $\beta = 0$ and $\Omega_\nu \simeq 0$. Thick (thin) curves show the constraints deriving from CMB and deep sample data (from CMB data only). Solid curves refer to the (i) case (WMAP+2dF). Dashed curves refer to the (ii) case (PLANCK+SDSS). In the sequel we shall examine in detail models corresponding to the points labeled a, b, c, d, e and others. The location of the CM--model of Figs. \ref{['t2n']} and \ref{['c2n']} is indicated by an open box. The two locations indicated by an open circle and a cross will also be considered in detail below. This Figure is somehow analogous to Fig. 2 in Hannestad, 2005.
  • Figure 4: Correlation between $\beta$ and the other model parameters for the W case (WMAP+2dF); dashed lines refer to CMB data only.
  • Figure 5: Correlation between $\beta$ and the other model parameters for the P case (PLANCK+SDSS); dashed lines refer to CMB data only.
  • ...and 4 more figures