arXiv subjects

M. Orito

Publications and source records attributed to M. Orito.

9 recordsLinked to original sources

arXiv2004

Constraints on Resonant Particle Production during Inflation from the Matter and CMB Power Spectra

We analyze the limits on resonant particle production during inflation based upon the power spectrum of fluctuations in matter and the cosmic microwave background. We show that such a model is consistent with features observed in the matter power spectrum deduced from galaxy surveys and damped Lyman-alpha systems at high redshift. It also provides an alternative explanation for the excess power observed in the power spectrum of the cosmic microwave background fluctuations in the range of 1000 < l < 3500. For our best-fit models, epochs of resonant particle creation reenter the horizon at wave numbers ~ 0.4 and/or 0.2 (h/Mpc). The amplitude and location of these features correspond to the creation of fermion species of mass ~ 1-2 Mpl during inflation with a coupling constant between the inflaton field and the created fermion species of near unity. Although the evidence is marginal, if this interpretation is correct, this could be one of the first observational hints of new physics at the Planck scale.

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arXiv2003

New Classes of Cosmic Energy and Primordial Black-Hole Formation

It has recently been suggested that the formation of horizon-size primordial black hole (PBH) from pre-existing density fluctuations is effective during the cosmic QCD phase transition. In this Letter we discuss the dependence of PBH formation on effective relativistic degrees of freedom, $g_{\rm eff}$ during the cosmic QCD phase transition. Our finding is important in the light of recent cosmological arguments of several new classes of cosmic energy that appear from universal neutrino degeneracy, quintessential inflation, and dark radiation in brane world cosmology. Extra-energy component from the standard value in these new cosmological theories is represented as an effective radiation in terms of $g_{\rm eff}$. We conclude that the PBH formation during QCD phase transition becomes more efficient if negative extra-component of the cosmic energy is allowed because of the increase of the duration of the QCD phase transition, which leads to smaller mass scale of PBHs. This suggests larger probability of finding more PBHs if the dark radiation exists as allowed in the brane world cosmology.

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arXiv2002

Observational Constraints on Dark Radiation in Brane Cosmology

We analyze the observational constraints on brane-world cosmology whereby the universe is described as a three-brane embedded in a five-dimensional anti-de Sitter space. In this brane-universe cosmology, the Friedmann equation is modified by the appearance of extra terms which derive from existence of the extra dimensions. In the present work we concentrate on the ``dark radiation'' term which diminishes with cosmic scale factor as $a^{-4}$. We show that, although the observational constraints from primordial abundances allow only a small contribution when this term is positive, a much wider range of negative values is allowed. Furthermore, such a negative contribution can reconcile the tension between the observed primordial $\he4$ and D abundances. We also discuss the possible constraints on this term from the power spectrum of CMB anisotropies in the limit of negligible cosmological perturbation on the brane world. We show that BBN limits the possible contribution from dark radiation just before the nucleosynthesis epoch to lie between -65% and $+5%$ of the background photon energy density. Combining this with the CMB constraint reduces this range to between -24% and $+3.5%$ at the $2σ$ confidence level.

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arXiv2002

Constraints on Neutrino Degeneracy from the Cosmic Microwave Background and Primordial Nucleosynthesis

We reanalyze the cosmological constraints on the existence of a net universal lepton asymmetry and neutrino degeneracy based upon the latest high resolution CMB sky maps from BOOMERANG, DASI, and MAXIMA-1. We generate likelihood functions by marginalizing over $(\omegab h^2,\xinumt, \xinue, Ω_Λ,h,n)$ plus the calibaration uncertainties. We consider flat $Ω_M + Ω_Λ= 1$ cosmological models with two identical degenerate neutrino species, $\xinumt \equiv \vert \xinum \vert = \vert \xinut \vert$ and a small $\xinue$. We assign weak top-hat priors on the electron-neutrino degeneracy parameter $\xinue$ and $Ω_b h^2$ based upon allowed values consistent with the nucleosynthesis constraints as a function of $\xinumt$. The change in the background neutrino temperature with degeneracy is also explicitly included, and Gaussian priors for $h = 0.72 \pm 0.08$ and the experimental calibration uncertainties are adopted. The marginalized likelihood functions show a slight (0.5$σ$) preference for neutrino degeneracy. Optimum values with two equally degenerate $μ$ and $τ$ neutrinos imply $\xinumt = 1.0^{+0.8 (1σ)}_{-1.0 (0.5σ)}$, from which we deduce $ξ_{ν_e} = 0.09^{+0.15}_{-0.09}$, and $Ω_b h^2 = 0.021^{+0.06}_{- 0.002}$. The $2σ$ upper limit becomes $ \xinumt \le 2.1$, which implies $ξ_{ν_e} \le 0.30$, and $Ω_b h^2 \le 0.030$. For only a single large-degeneracy species the optimal value is $\vert \xinum \vert$ or $\vert \xinut \vert = 1.4$ with a $2σ$ upper limit of $\vert \xinum \vert$ or $\vert \xinut \vert \le 2.5$

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arXiv2002

Constrainting Cosmic Quintessence

A generic feature of cosmic quintessence models is the possibility of significant energy density in the scalar field during the radiation dominated epoch. This possibility is even greater if the quintessence field begins in a kinetic-dominated regime, for example as might be generated at the end of "quintessential inflation." As such, these models can be constrained by primordial nucleosynthesis and the epoch of photon decoupling. Here, we analyze both kinetic dominated and power-law quintessence fields (with and without a supergravity correction). We quantify the allowed initial conditions and effective-potential parameters. We also deduce constraints on the epoch of matter creation at the end of quintessential inflation.

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arXiv2002

Universal Lepton Asymmetry: New Constraints from the Cosmic Microwave Background and Primordial Nucleosynthesis

We study the primordial nucleosynthesis and cosmic age in the presence of a net lepton asymmetry as well as baryon asymmetry. We explore a previously unnoted region of the parameter space in which very large baryon densities $0.1 \le Ω_b \le 1$ can be accommodated within the light-element constraints from primordial nucleosynthesis. This parameter space consists of $ν_μ$ and $ν_τ$ degeneracies with a small $ν_e$ degeneracy. Constraints from cosmic microwave background fluctuations are also discussed (orito00).

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arXiv2002

Constraints on Cosmic Quintessence and Quintessential Inflation

Recently, attempts have been made to understand the apparent near coincidence of the present dark energy and matter energy in terms of a dynamical attractor-like solution for the evolution of a scalar field. In these models the field couples with the dominant constituent and only acts like a cosmological constant after the onset of the matter-diminated epoch. A generic feature of such solutions, however, is the possibility of significant energy density in the scalar field during the radiation-dominated epoch. This possibility is even greater if the quintessence field begins in a kinetic-dominated regime generated at the end of quintessential inflation. As such, these models can affect and be constrained by primordial nucleosynthesis and the epoch of of photon decoupling. Here, we analyze one popular form of the quintessence field (with and without a supergravity correction) and quantify constraints on the allowed initial conditions and parameters for the effective potential. We also deduce constraints on the epoch of matter creation at the end of quintessential inflation.

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arXiv2001

Neutrino Degeneracy and Decoupling: New Limits from Primordial Nucleosynthesis and the Cosmic Microwave Background

We reanalyze the cosmological constraints on the existence of a net universal lepton asymmetry and neutrino degeneracy. We show that neutrinos can begin to decouple at higher temperatures than previous estimates due to several corrections which diminish the neutrino reaction rate. These decoupled neutrinos are therefore not heated as the particle degrees of freedom change. The resultant ratio of the relic neutrino-to-photon temperatures after $e^\pm$ annihilation can then be significantly reduced by more than a factor of two from that of the standard nondegenerate ratio. This changes the expansion rate and subsequent primordial nucleosynthesis, photon decoupling, and structure formation. In particular we analyze physically plausible lepton-asymmetric models with large $ν_μ$ and $ν_τ$ degeneracies together with a moderate $ν_e$ degeneracy. We show that the nucleosynthesis by itself permits very large neutrino degeneracies $0 \le \xinum$, $\xinut \le 40$, $0 \le \xinue \le 1.4$ together with large baryon densities $0.1 \le Ω_b \h502 \le 1$ as long as some destruction of primordial lithium has occurred. We also show that structure formation and the power spectrum of the cosmic microwave background allows for the possibility of an $Ω= 1$, $Ω_Λ= 0.4$, cosmological model for which there is both significant lepton asymmetry ($| \xinum | = | \xinut | \approx 11$) and a relatively large baryon density ($Ω_b \h502 \approx 0.2$). Our best-fit neutrino-degenerate, high-baryon-content models are mainly distinguished by a suppression of the second peak in the microwave background power spectrum. This is consistent with the recent high resolution data from BOOMERANG and MAXIMA-1.

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arXiv1996

Geometrical Effects of Baryon Density Inhomogeneities on Primordial Nucleosynthesis

We discuss effects of fluctuation geometry on primordial nucleosynthesis. For the first time we consider condensed cylinder and cylindrical-shell fluctuation geometries in addition to condensed spheres and spherical shells. We find that a cylindrical shell geometry allows for an appreciably higher baryonic contribution to be the closure density ($Ω_b h_{50}^2 \la 0.2$) than that allowed in spherical inhomogeneous or standard homogeneous big bang models. This result, which is contrary to some other recent studies, is due to both geometry and recently revised estimates of the uncertainties in the observationally inferred primordial light-element abundances. We also find that inhomogeneous primordial nucleosynthesis in the cylindrical shell geometry can lead to significant Be and B production. In particular, a primordial beryllium abundance as high as [Be] = 12 + log(Be/H) $\approx -3$ is possible while still satisfying all of the light-element abundance constraints.

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