arXiv subjects

Qing-Guo Huang

Publications and source records attributed to Qing-Guo Huang.

At least 127 records · Page 7Linked to original sources

arXiv2015

No evidence for the blue-tilted power spectrum of relic gravitational waves

In this paper, we constrain the tilt of the power spectrum of relic gravitational waves by combining the data from BICEP2/Keck array and Planck (BKP) and the Laser Interferometer Gravitational-Waves Observatory (LIGO). From the data of BKP B-modes, the constraint on the tensor tilt is $n_t=0.66^{+1.83}_{-1.44}$ at the $68%$ confidence level. By further adding the LIGO upper limit on the energy density of gravitational waves, the constraint becomes $n_t=-0.76^{+1.37}_{-0.52}$ at the $68%$ confidence level. We conclude that there is no evidence for a blue-tilted power spectrum of relic gravitational waves and either sign of the index of tensor power spectrum is compatible with the data.

astro-ph.CO↗

arXiv2014

Constraint on the primordial gravitational waves from the joint analysis of BICEP2 and Planck HFI 353 GHz dust polarization data

We make a joint analysis of BICEP2 and recently released Planck HFI 353 GHz dust polarization data, and find that there is no evidence for the primordial gravitational waves and the bound on the tensor-to-scalar ratio becomes $r<0.083$ at $95%$ confidence level in the base $Λ$CDM + tensor model. Extending to the model with running of scalar spectral index, the bound is a little bit relaxed to $r<0.116$ at $95%$ confidence level. Our results imply that the inflation model with a single monomial potential is marginally disfavored at around $95%$ confidence level. Especially, the $m^2ϕ^2/2$ inflation model is disfavored at more than $2σ$ level. However, the Starobinsky inflation model gives a nice fit.

astro-ph.CO↗

arXiv2014

Constraints on the cosmological parameters from BICEP2, Planck and WMAP

In this paper we constrain the cosmological parameters, in particular the tilt of tensor power spectrum, by adopting Background Imaging of Cosmic Extragalactic Polarization (B2), Planck released in 2013 (P13) and Wilkinson Microwaves Anisotropy Probe 9-year Polarization (WP) data. We find that a blue tilted tensor power spectrum is preferred at more than $3σ$ confidence level if the data from B2 are assumed to be totally interpreted as the relic gravitational waves, but a scale invariant tensor power spectrum is consistent with the data once the polarized dust is taken into account. The recent Planck 353 GHz HFI dust polarization data imply that the B2 data are perfectly consistent with there being no gravitational wave signal.

astro-ph.CO↗

arXiv2014

An accurate determination of the Hubble constant from Baryon Acoustic Oscillation datasets

Even though the Hubble constant cannot be significantly determined by the low-redshift Baryon Acoustic Oscillation (BAO) data alone, it can be tightly constrained once the high-redshift BAO data are combined. Combining BAO data from 6dFGS, BOSS DR11 clustering of galaxies, WiggleZ and $z=2.34$ from BOSS DR11 quasar Lyman-$α$ forest lines, we get $H_0=68.17^{+1.55}_{-1.56}$ km s$^{-1}$ Mpc$^{-1}$. In addition, adopting the the simultaneous measurements of $H(z)$ and $D_A(z)$ from the two-dimensional two-point correlation function from BOSS DR9 CMASS sample and two-dimensional matter power spectrum from SDSS DR7 sample, we obtain $H_0=68.11\pm1.69$ km s$^{-1}$ Mpc$^{-1}$. Finally, combining all of the BAO datasets, we conclude $H_0=68.11\pm 0.86$ km s$^{-1}$ Mpc$^{-1}$, a 1.3% determination.

astro-ph.CO↗

arXiv2014

The (p,q) inflation model

In this paper we propose a new inflation model named (p,q) inflation model in which the inflaton potential contains both positive and negative powers of inflaton field in the polynomial form. We will show that such a simple model can easily generate a large amplitude of tensor perturbation and a negative running of spectral index with large absolute value.

astro-ph.CO↗

arXiv2014

An analytic calculation of the growth index for $f(R)$ dark energy model

We derive the analytic formula of the growth index for $f(R)$ dark energy model where the effect on the growth of matter density perturbation $δ_m$ from modified gravity (MG) is encoded in the effective Newton coupling constant $G_{\rm eff}$ in MG (or equivalently $g\equiv {G_{\rm eff}/ G}$). Based on the analytic formula, we propose that the parameter $g$ can be directly figured out by comparing the observed growth rate $f_g\equiv d\lnδ_m/d\ln a$ to the prediction of $f_g$ in general relativity.

astro-ph.CO↗

arXiv2014

Constraints on the extensions to the base $Λ$CDM model from BICEP2, Planck and WMAP

Recently Background Imaging of Cosmic Extragalactic Polarization (B2) discovered the relic gravitational waves at $7.0σ$ confidence level. However, the other cosmic microwave background (CMB) data, for example Planck data released in 2013 (P13), prefer a much smaller amplitude of the primordial gravitational waves spectrum if a power-law spectrum of adiabatic scalar perturbations is assumed in the six-parameter $Λ$CDM cosmology. In this paper, we explore whether the $w$CDM model and the running spectral index can relax the tension between B2 and other CMB data. In particular, we find that a positive running of running of spectral index is preferred at $1.7σ$ level from the combination of B2, P13 and WMAP Polarization data.

astro-ph.CO↗

arXiv2014

Probing the primordial Universe from the low-multipole CMB data

Since the temperature fluctuations in cosmic microwave background (CMB) on large-angular scales probe length scales that were super-horizon sized at photon decoupling and hence insensitive to microphysical processes, the low-multipole CMB data are supposed to be a good probe to the physics of the primordial Universe. In this letter we will constrain the cosmological parameters in the base $Λ$CDM model with tensor perturbations by only using low-multipole CMB data, including Background Imaging of Cosmic Extragalactic Polarization (B2), Planck released in 2013 (P13) and Wilkinson Microwaves Anisotropy Probe 9-year data (W9). We find that a red tilted power spectrum of relic gravitational waves is compatible with the data, but a blue tilted power spectrum of scalar perturbations on the large scales is preferred at around $2σ$ confidence level.

astro-ph.CO↗

arXiv2014

Constraint on inflation model from BICEP2 and WMAP 9-year data

Even though Planck data released in 2013 (P13) is not compatible with Background Imaging of Cosmic Extragalactic Polarization (B2) and some local cosmological observations, including Supernova Legacy Survey (SNLS) samples and $H_0$ prior from Hubble Space Telescope (HST) etc, Wilkinson Microwaves Anisotropy Probe 9-year data (W9) is consistent with all of them in the base six-parameter $Λ$CDM+tensor cosmology quite well. In this letter, we adopt the combinations of B2+W9 and B2+W9+SNLS+BAO+HST to constrain the cosmological parameters in the base six-parameter $Λ$CDM+tensor model with $n_t=-r/8$, where r and $n_t$ are the tensor-to-scalar ratio and the tilt of relic gravitational wave spectrum, and BAO denotes Baryon Acoustic Oscillation. We find that the Harrison-Zel'dovich (HZ) scale invariant scalar power spectrum is consistent with both data combinations, chaotic inflation is marginally disfavored by the data at around $2σ$ level, but the power-law inflation model and the inflation model with inverse power-law potential can fit the data nicely.

astro-ph.CO↗

arXiv2014

The Tilt of Primordial Gravitational Waves Spectra from BICEP2

In this paper we constrain the tilt of the spectra of primordial gravitational waves from Background Imaging of Cosmic Extragalactic Polarization (BICEP2) data only. We find $r=0.21_{-0.10}^{+0.04}$ and $n_t=-0.06_{-0.23}^{+0.25}$ (at $68\%$ C.L.) which implies that a scale-invariant primordial gravitational waves spectra is consistent with BICEP2 nicely. Our results provide strong evidence for supporting inflation model, and the alternative models, for example the ekpyrotic model which predicts $n_t=2$, are ruled out at more than $5σ$ significance.

astro-ph.CO↗

arXiv2014

Hint of relic gravitational waves in the Planck and WMAP data

Relic gravitational waves (RGWs) leave well-understood imprints on the anisotropies in the temperature and polarization of cosmic microwave background (CMB) radiation. In the TT and TE information channels, which have been well observed by WMAP and Planck missions, RGWs compete with density perturbations mainly at low multipoles. It is dangerous to include high-multipole CMB data in the search for gravitational waves, as the spectral indices may not be constants. In this paper, we repeat our previous work [W.Zhao & L.P.Grishchuk, Phys.Rev.D {\bf 82}, 123008 (2010)] by utilizing the Planck TT and WMAP TE data in the low-multipole range $\ell\le100$. We find that our previous result is confirmed {with higher confidence}. The constraint on the tensor-to-scalar ratio from Planck TT and WMAP TE data is $r\in [0.06,~0.60]$ (68% C.L.) with the maximum likelihood at around $r\sim 0.2$. Correspondingly, the spectral index at the pivot wavenumber $k_*=0.002$Mpc$^{-1}$ is $n_s=1.13^{+0.07}_{-0.08}$, which is larger than 1 at more than $1σ$ level. So, we conclude that the new released CMB data indicate a stronger hint for the RGWs with the amplitude $r\sim 0.2$, which is hopeful to be confirmed by the imminent BICEP and Planck polarization data.

astro-ph.CO↗

arXiv2014

The Dark Side of the Universe after Planck

Recently released Planck data implies a smaller Hubble constant $H_0$ than that from Hubble Space Telescope project (HST) and a larger percentage of the matter components $Ω_m$ compared to Supernova Legacy Survey (SNLS) in $Λ$CDM model. In this paper we found that even though the tension on $H_0$ between Planck and HST can be relaxed if the dark radiation is introduced ($ΔN_{\rm eff}=0.536_{-0.224}^{+0.229}$ at $68\%$ CL from the datasets of Planck+WMAP Polarization (WP)+baryon acoustic oscillation (BAO)+the combination of supernova Union2.1 compilation of 580 SNe (Union2.1)+HST), $Ω_m$ from Planck is still not nicely compatible with that from SNLS. The tensions between Planck and other astrophysical datasets can be significantly relaxed in $w$CDM model, and the combination of these datasets prefers a phantom-like dark energy at more than $95\%$ CL: $w=-1.15\pm 0.07$ and $w=-1.16\pm 0.06$ at $68\%$ CL from Planck+WP+BAO+Union2.1+HST and Planck+WP+BAO+SNLS+HST respectively. From the statistical point of view, there is no evidence for a time-evolving equation of state ($Δχ^2=-0.3$ compared to a constant equation of state for the combination of Planck+WP+BAO+SNLS+HST).

astro-ph.CO↗

arXiv2014

A polynomial f(R) inflation model

Motivated by the ultraviolet complete theory of quantum gravity, for example the string theory, we investigate a polynomial $f(R )$ inflation model in detail. We calculate the spectral index and tensor-to-scalar ratio in the $f(R )$ inflation model with the form of $f(R )=R+{R^2\over 6M^2}+{λ_n\over 2n}{R^n\over (3M^2)^{n-1}}$. Compared to Planck 2013, we find that $R^n$ term should be exponentially suppressed, i.e. $|λ_n|\lesssim 10^{-2n+2.6}$.

hep-th↗

arXiv2014

Mass-Varying Massive Gravity

It has recently been shown that the graviton can consistently gain a constant mass without introducing the Boulware-Deser ghost. We propose a gravity model where the graviton mass is set by a scalar field and prove that this model is free of the Boulware-Deser ghost by analyzing its constraint system and showing that two constraints arise. We also initiate the study of the model's cosmic background evolution and tentatively discuss possible cosmological implications of this model. In particular, we consider a simple scenario where the scalar field setting the graviton mass is identified with the inflaton and the graviton mass evolves from a high to a low energy scale, giving rise to the current cosmic acceleration.

hep-th↗

arXiv2013

Generalized massive gravity in arbitrary dimensions and its Hamiltonian formulation

We extend the four-dimensional de Rham-Gabadadze-Tolley (dRGT) massive gravity model to a general scalar massive-tensor theory in arbitrary dimensions, coupling a dRGT massive graviton to multiple scalars and allowing for generic kinetic and mass matrix mixing between the massive graviton and the scalars, and derive its Hamiltonian formulation and associated constraint system. When passing to the Hamiltonian formulation, two different sectors arise: a general sector and a special sector. Although obtained via different ways, there are two second class constraints in either of the two sectors, eliminating the BD ghost. However, for the special sector, there are still ghost instabilities except for the case of two dimensions. In particular, for the special sector with one scalar, there is a "second BD ghost".

hep-th↗

arXiv2013

Constraints on single-field inflation with WMAP, SPT and ACT data -- A last-minute stand before Planck

We constrain models of single field inflation with the pre-\textit{Planck} CMB data. The data used here is the 9-year Wilkinson Microwave Anisotropy Probe (\textit{WMAP}) data, South Pole Telescope (SPT) data and Atacama Cosmology Telescope (ACT) data. By adding in running of spectral index parameter, we find that the $χ^2$ is improved by a factor of $Δχ^2=8.44$, which strongly indicates the preference of this parameter from current data. In addition, we find that the running of spectral index $α_s$ does not change very much even if we switch to different pivot scales, which suggests that the power law expansion of power spectrum is accurate enough till the 1st order term. Furthermore, we find that the joint constraints on $r-n_{s}$ give very tight constraints on single-field inflation models, and the models with power law potential $ϕ^{p}$ can only survive if $0.9 \lesssim p \lesssim 2.1$, so a large class of inflation models have already been ruled out before \textit{Planck} data. Finally, we use the $f_{NL}$ data to constrain the non-trivial sound speed $c_s$. We find that the current constraint is dominated by the power spectrum constraints which have some inconsistency with the constraints from $f_{NL}$. This poses important questions of consistency between power spectrum and bispectrum of \textit{WMAP} data.

astro-ph.CO↗

arXiv2013

Confronting brane inflation with Planck and pre-Planck data

In this paper, we compare brane inflation models with the Planck data and the pre-Planck data (which combines WMAP, ACT, SPT, BAO and H0 data). The Planck data prefer a spectral index less than unity at more than 5σconfidence level, and a running of the spectral index at around 2σconfidence level. We find that the KKLMMT model can survive at the level of 2σonly if the parameter $β$ (the conformal coupling between the Hubble parameter and the inflaton) is less than $\mathcal{O}(10^{-3})$, which indicates a certain level of fine-tuning. The IR DBI model can provide a slightly larger negative running of spectral index and red tilt, but in order to be consistent with the non-Gaussianity constraints from Planck, its parameter also needs fine-tuning at some level.

astro-ph.CO↗

arXiv2013

$g_{\rm NL}$ in the curvaton model constrained by PLANCK

As a simplest extension to the mass-term curvaton model, the curvaton model with a polynomial potential can relax the restricted constraint from PLANCK due to the non-linear dynamics of curvaton field before it decays. We find that there is still a big room for producing a large negative $g_{\rm NL}$, but not positive $g_{\rm NL}$. For example, we only need around 10% "tuning" for $-g_{\rm NL}>10^4$.

astro-ph.CO↗