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Chia-Min Lin

Publications and source records attributed to Chia-Min Lin.

At least 55 records · Page 3Linked to original sources
arXiv2013

Delta-N Formalism for Curvaton with Modulated Decay

In this paper, the curvature perturbation generated by the modulated curvaton decay is studied by a direct application of $δN$-formalism. Our method has a sharp contrast with the {\it non-linear formalism} which may be regarded as an indirect usage of $δN$-formalism. We first show that our method can readily reproduce results in previous works of modulation of curvaton. Then we move on to calculate the case where the curvaton mass (and hence also the decay rate) is modulated. The method can be applied to the calculation of the modulation in the freezeout model, in which the heavy species are considered instead of the curvaton. Our method explains curvaton and various modulation on an equal footing.

astro-ph.CO↗
arXiv2013

Primordial Black Holes from the inflating curvaton

The primordial black hole (PBH) formation is studied in light of the inflating curvaton. The typical scale of the PBH formation is determined by curvaton inflation, which may generate PBH with $10^{14}\mathrm{g}\le M_\mathrm{PBH}\le 10^{38}\mathrm{g}$ when curvaton inflation gives the number of e-foldings $5\leq N_2\leq 38$. The non-Gaussianity of the inflating curvaton does not prevent the PBH formation.

hep-ph↗
arXiv2013

Primordial Black Holes from Passive Density Fluctuations

In this paper, we show that if passive fluctuations are considered, primordial black holes (PBHs) can be easily produced in the framework of single-field, slow-roll inflation models. The formation of PBHs is due to the blue spectrum of passive fluctuations and an enhancement of the spectral range which exits horizon near the end of inflation. Therefore the PBHs are light with masses $\lesssim 10^{15}g$ depending on the number of e-folds when the scale of our observable universe leaves horizon. These PBHs are likely to have evaporated and cannot be a candidate for dark matter but they may still affect the early universe.

hep-ph↗
arXiv2012

Non-Gaussianity from two right-handed sneutrino curvaton decays

In this paper, we consider the effect of two right-handed sneutrino curvaton decays and investigate the parameter space. We compare the difference of the result between single- and two-curvaton cases. We find one Yukawa coupling of the right-handed snetrinos can be as large as $λ\sim 0.1$ while the other one is much smaller which is consistent with the idea that only one generation of the neutrino mass may be much smaller than others. When the curvatons decay, we assume both of them subdominate the energy density of the universe. We find that, unlike a single curvaton case, here a small or negative, as well as a large $f_{NL}$ can be generated.

hep-ph↗
arXiv2012

Affleck-Dine baryogenesis in inflating curvaton scenario with O($10-10^2$TeV) mass moduli curvaton

We study the Affleck-Dine (AD) baryogenesis in the inflating curvaton scenario, when the curvaton is a moduli field with O($10-10^2$TeV) mass. A moduli field with such mass is known to be free from the Polonyi problem, and furthermore its decay products can explain the present cold dark matter abundance. In our scenario, it further explains the primordial curvature perturbation and the present baryon density all together. The current observational bound on the baryon isocurvature perturbation, which severely constrains the AD baryogenesis with the original oscillating moduli curvaton scenario, is shown to put practically negligible constraint if we replace the oscillating curvaton with the inflating curvaton.

hep-ph↗
arXiv2011

Kinematically Blocked Curvaton

In this paper, we investigate the idea that the decay of a curvaton is kinematically blocked and show that the coupling constant for curvaton decay can be as large as ${\cal O}(1)$. We also find in this case the lower bound of the Hubble parameter at horizon exit from big bang nucleosynthesis (BBN) is $H_\ast \gae 7.2 \times 10^{-9}M_P \sim 10^{10} {GeV}$. Similar to conventional curvaton scenario, the nonlinear parameter can be as large as $f_{NL}=100$.

astro-ph.CO↗
arXiv2011

Cosmon as the Modulon: Non-Gaussianity from Dark Energy

In this paper, we show that the idea of growing neutrino can result in a modulated reheating effect and produce detectable non-Gaussianity in the model where the Higgs triplet from type II seesaw mechanism plays the role of the inflaton in chaotic inflation.

hep-ph↗
arXiv2011

Bimodal/Schizophrenic Neutrino As a Bridge between Inflation and Dark Energy

We consider the possibility to combine inflection point inflation and growing neutrino dark energy in a particular setup of bimodal/schizophrenic neutrino model in the framework of MSSM$\otimes U(1)_{B-L}$. In order to obtain a varying neutrino mass, we make an assumption that a soft mass of $\tilde{Z'}_{BL}$ depends on a scalar field which plays the role of a cosmon field. We also investigate the possible effects of the cosmon field in the early universe such as modulated reheating and found that the induced density perturbation is negligible.

hep-ph↗
arXiv2010

Inflaton versus Curvaton in Higher Dimensional Gauge Theories

We construct a model of cosmological inflation and perturbation based on the higher-dimensional gauge theory. The inflaton and curvaton are the scalar fields arising from the extra space components of the gauge field living in more than four dimensions. We take the six-dimensional (6D) Yang-Mills theory compactified on $T^2$ as a toy model, and apply the one-loop effective potential of the inflaton and the curvaton to the curvaton scenario. We have found that the curvaton is subdominant for the linear curvature perturbation, but that a significant non-Gaussianity and a sizable tensor to scalar ratio are generated.

hep-ph↗
arXiv2010

Hilltop Supernatural Inflation

In this talk, I will explain how to reduce the spectral index to be n_s=0.96 for supernatural inflation. I will also show the constraint to the reheating temperature from Big Bang Nucleosynthesis of both thermal and non-thermal gravitino production.

hep-ph↗
arXiv2010

Hilltop Supernatural Inflation and Gravitino Problem

In this paper, we explore the parameter space of hilltop supernatural inflation model and show the regime within which there is no gravitino problem even if we consider both thermal and nonthermal production mechanisms. We make plots for the allowed reheating temperature as a function of gravitino mass by constraints from big-bang nucleosynthesis. We also plot the constraint when gravitino is assumed to be stable and plays the role of dark matter.

hep-ph↗
arXiv2009

Comments on SUSY inflation models on the brane

In this paper we consider a class of inflation models on the brane where the dominant part of the inflaton scalar potential does not depend on the inflaton field value during inflation. In particular, we consider supernatural inflation, its hilltop version, A-term inflation, and supersymmetric (SUSY) D- and F-term hybrid inflation on the brane. We show that the parameter space can be broadened, the inflation scale generally can be lowered, and still possible to have the spectral index $n_s=0.96$.

hep-ph↗
arXiv2009

Right-Handed Sneutrino Curvaton and non-Gaussianity

In this paper, we explore the parameter space for a Right-Handed (RH) sneutrino curvaton that can generate large non-Gaussianity without assuming any particular inflation sector. The mass of the RH sneutrino is suggested from a discussion on the initial condition of the curvaton field. It is shown that a small Yukawa coupling is generally required for a successful RH sneutrino curvaton. However, the Yukawa coupling can be larger if we consider the braneworld scenario. Some general discussion about the spectral index in curvaton scenario is also provided.

hep-ph↗
arXiv2009

Large non-Gaussianity generated at the end of Extended D-term Hybrid Inflation

In this paper, we show that if we extend D-term hybrid inflation by adding a light scalar field which couples to a waterfall field, large non-Gaussianity can be generated at the end of inflation. Contribution of cosmic strings generated after D-term inflation to the Cosmic Microwave Background (CMB) angular power spectrum can be as low as 10% and this also evade the spectral index problem.

hep-ph↗
arXiv2009

Triple Unification of Inflation, Dark matter and Dark energy in Chaotic Braneworld Inflation

In this paper, we show that in the framework of chaotic braneworld inflation, after preheating, the remaining oscillating inflaton field can play the role of dark matter with the observed level. Augmented by a non-zero effective cosmological constant $Λ_4$ on the brane, triple unification of inflation, dark matter and dark energy by a single field is realized. Our model perhaps is the simplest one in the market of theories to achieve triple unification.

hep-ph↗
arXiv2009

Supernatural A-term Inflation

Following \cite{Lin:2009yt}, we explore the parameter space of the case when the supersymmetry (SUSY) breaking scale is lower, for example, in gauge mediated SUSY breaking model. During inflation, the form of the potential is $V_0$ plus MSSM (MSSM stands for Minimal Supersymmetric Standard Model) (or A term (It is called A-term inflation when the inflaton field is any direction (gauge or singlet) that generates an A-term.)) inflation. We show that the model works for a wide range of the potential $V_0$ with the soft SUSY breaking mass $m\sim O(1)$ TeV. The implication to MSSM (or A-term) inflation is that the flat directions which is lifted by the non-renormalizable terms described by the superpotential $W=λ_p ϕ^{p-1}/M^{p-3}_P$ with $p=4$ and $p=5$ are also suitable to be an inflaton field for $λ_p=O(1)$ provided there is an additional false vacuum term $V_0$ with appropriate magnitude. The flat directions corresponds to $p=6$ also works for $0 \lae V_0/M_P^4 \lae 10^{-40}$.

hep-ph↗
arXiv2009

Reducing the Spectral Index in Supernatural Inflation

Supernatural inflation is an attractive model based just on a flat direction with soft SUSY breaking mass terms in the framework of supersymmetry. The beauty of the model is inferred from its name that the model needs no fine-tuning. However, the prediction of the spectral index is $n_s \gae 1$, in contrast to experimental data. In this paper, we show that the beauty of supernatural inflation with the spectral index reduced to $n_s=0.96$ without any fine-tuning, by considering the general feature that a flat direction is lifted by a non-renormalizable term with an A-term.

hep-ph↗