http://arxiv.org/abs/2205.11559
We estimate the viable parameter regions for the model parameters in the degenerate higher-order scalar-tensor (DHOST) theories from Planck 2018 likelihoods with the Markov-Chain Monte-Carlo (MCMC) simulation. In our previous paper, we developed a Boltzmann solver incorporating the effective field theory (EFT) approach parameterised by the six kinds of functions of time, $\alpha_i$ $(i={\rm B},{\rm K},{\rm T},{\rm M},{\rm H})$ and $\beta_1$, which can describe the DHOST theories. Performing the MCMC simulations with the Boltzmann solver, we obtain the confidence ranges of the model parameters in the DHOST theories. We consider a simple model with $\alpha_{\rm B}=\alpha_{\rm T}=\alpha_{\rm M}=\alpha_{\rm H}=0$ and $\alpha_{\rm K},\beta_1\ne 0$, in the $\Lambda$CDM background, and then obtain $\beta_1=0.032_{-0.016}^{+0.013}$ (68\% c.l.) at the present time. Next, we consider the model proposed by Crisostomi and Koyama in which the arbitrary functions of the scalar field in the original action of the DHOST theories are fixed to be $\mathcal{L}{\rm DHOST} = X + c_3X\Box\phi/\Lambda^3+ (M{\rm pl}^2/2+c_4X^2/\Lambda^6)R$ so that the background self-accelerating solution exists. In this model, we consistently treat the background and the perturbations, and obtain $c_3 = 1.59^{+0.26}_{-0.28}$ and $c_4<0.0088$ (68\% c.l.).
T. Hiramatsu
Wed, 25 May 22
8/56
Comments: 11 pages, 4 figures, 1 table
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