0000000000020962
AUTHOR
Wan-il Park
showing 17 related works from this author
Impact of CP-violation on neutrino lepton number asymmetries revisited
2017
We revisit the effect of the (Dirac) CP-violating phase on neutrino lepton number asymmetries in both mass- and flavor-basis. We found that, even if there are sizable effects on muon- and tau-neutrino asymmetries, the effect on the asymmetry of electron-neutrinos is at most similar to the upper bound set by BBN for initial neutrino degeneracy parameters smaller than order unity. We also found that, for the asymmetries in mass-basis, the changes caused by CP-violation is of sub-\% level which is unlikely to be accesible neither in the current nor in the forthcoming experiments.
The (relative) size does not matter in inflation
2015
We show that a tiny correction to the inflaton potential can make critical changes in the inflationary observables for some types of inflation models.
Peccei–Quinn field for inflation, baryogenesis, dark matter, and much more
2016
We propose a scenario of brane cosmology in which the Peccei-Quinn field plays the role of the inflaton and solves simultaneously many cosmological and phenomenological issues such as the generation of a heavy Majorana mass for the right-handed neutrinos needed for seesaw mechanism, MSSM $\mu$-parameter, the right amount of baryon number asymmetry and dark matter relic density at the present universe, together with an axion solution to the strong CP problem without the domain wall obstacle. Interestingly, the scales of the soft SUSY-breaking mass parameter and that of the breaking of $U(1)_{\rm PQ}$ symmetry are lower bounded at $\mathcal{O}(10) {\mathrm TeV}$ and $\mathcal{O}(10^{11}) {\ma…
Lepton number asymmetries and the lower bound on the reheating temperature
2017
We show that the reheating temperature of a matter-domination era in the early universe can be pushed down to the neutrino decoupling temperature at around $2 \ {\rm MeV}$ if the reheating takes place through non-hadronic decays of the dominant matter and neutrino-antineutrino asymmetries are still large enough, $|L| \gtrsim \mathcal{O}(10^{-2})$ (depending on the neutrino flavor) at the end of reheating.
A full picture of large lepton number asymmetries of the Universe
2017
A large lepton number asymmetry of (0.1−1) at present Universe might not only be allowed but also necessary for consistency among cosmological data. We show that, if a sizeable lepton number asymmetry were produced before the electroweak phase transition, the requirement for not producing too much baryon number asymmetry through sphalerons processes, forces the high scale lepton number asymmetry to be larger than about 03. Therefore a mild entropy release causing (10-100) suppression of pre-existing particle density should take place, when the background temperature of the Universe is around T = (10−2-102) GeV for a large but experimentally consistent asymmetry to be present today. We also …
On large lepton number asymmetries of the Universe
2017
A large lepton number asymmetry of $\mathcal{O}(0.1-1)$ at present universe might not only be allowed but also necessary for consistency among cosmological data. We show that, if a sizeable lepton number asymmetry were produced before the electroweak phase transition, the requirement for not producing too much baryon number asymmetry through sphalerons processes, forces the high scale lepton number asymmetry to be larger than about $30$. Therefore a mild entropy release causing $\mathcal{O}(10-100)$ suppression of pre-existing particle density should take place, when the background temperature of the universe is around $T = \mathcal{O}(10^{-2} - 10^2) {\rm GeV}$ for a large but experimental…
Eternal hilltop inflation
2016
We consider eternal inflation in hilltop-type inflation models, favored by current data, in which the scalar field in inflation rolls off of a local maximum of the potential. Unlike chaotic or plateau-type inflation models, in hilltop inflation the region of field space which supports eternal inflation is finite, and the expansion rate $H_{EI}$ during eternal inflation is almost exactly the same as the expansion rate $H_*$ during slow roll inflation. Therefore, in any given Hubble volume, there is a finite and calculable expectation value for the lifetime of the "eternal" inflation phase, during which quantum flucutations dominate over classical field evolution. We show that despite this, i…
Spiral Inflation
2015
We propose a novel scenario of primordial inflation in which the inflaton goes through a spiral motion starting from around the top of a symmetry breaking potential. We show that, even though inflation takes place for a field value much smaller than Planck scale, it is possible to obtain relatively large tensor to scalar ratio ($r \sim 0.1$) without fine tuning. The inflationary observables perfectly match Planck data.
Higgs-portal assisted Higgs inflation with a sizeable tensor-to-scalar ratio
2014
We show that the Higgs portal interactions involving extra dark Higgs field can save generically the original Higgs inflation of the standard model (SM) from the problem of a deep non-SM vacuum in the SM Higgs potential. Specifically, we show that such interactions disconnect the top quark pole mass from inflationary observables and allow multi-dimensional parameter space to save the Higgs inflation, thanks to the additional parameters (the dark Higgs boson mass $m_{\phi}$, the mixing angle $\alpha$ between the SM Higgs $H$ and dark Higgs $\Phi$, and the mixed quartic coupling) affecting RG-running of the Higgs quartic coupling. The effect of Higgs portal interactions may lead to a larger t…
Gravitational waves from first order phase transitions as a probe of an early matter domination era and its inverse problem
2016
We investigate the gravitational wave background from a first order phase transition in a matter-dominated universe, and show that it has a unique feature from which important information about the properties of the phase transition and thermal history of the universe can be easily extracted. Also, we discuss the inverse problem of such a gravitational wave background in view of the degeneracy among macroscopic parameters governing the signal.
On the tensor-to-scalar ratio in large single-field inflation models
2015
We show that generically the tensor-to-scalar ratio in large single-field inflation scenarios is bounded to be larger than $\mathcal{O}(10^{-3})$ for the spectral index in the range favored by observations.
Resurrection of large lepton number asymmetries from neutrino flavor oscillations
2016
We numerically solve the evolution equations of neutrino three-flavor density matrices, and show that, even if neutrino oscillations mix neutrino flavors, large lepton number asymmetries are still allowed in certain limits by Big Bang Nucleosynthesis (BBN).
New- vs. chaotic- inflations
2015
We show that "spiralized" models of new-inflation can be experimentally identified mostly by their positive spectral running in direct contrast with most chaotic-inflation models which have negative runnings typically in the range of $\mathcal{O}(10^{-4}-10^{-3})$.
Flavor versus mass eigenstates in neutrino asymmetries: implications for cosmology
2017
We show that, if they exist, lepton number asymmetries ($L_\alpha$) of neutrino flavors should be distinguished from the ones ($L_i$) of mass eigenstates, since Big Bang Nucleosynthesis (BBN) bounds on the flavor eigenstates cannot be directly applied to the mass eigenstates. Similarly, Cosmic Microwave Background (CMB) constraints on mass eigenstates do not directly constrain flavor asymmetries. Due to the difference of mass and flavor eigenstates, the cosmological constraint on the asymmetries of neutrino flavors can be much stronger than conventional expectation, but not uniquely determined unless at least the asymmetry of the heaviest neutrino is well constrained. Cosmological constrain…
Beyond the dark matter effective field theory and a simplified model approach at colliders
2016
Direct detection of and LHC search for the singlet fermion dark matter (SFDM) model with Higgs portal interaction are considered in a renormalizable model where the full Standard Model (SM) gauge symmetry is imposed by introducing a singlet scalar messenger. In this model, direct detection is described by an effective operator m_q \bar{q} q \bar{\chi} \chi as usual, but the full amplitude for monojet + \not E_T involves two intermediate scalar propagators, which cannot be seen within the effective field theory (EFT) or in the simplified model without the full SM gauge symmetry. We derive the collider bounds from the ATLAS monojet + \not E_T as well as the CMS t\bar{t} + \not E_T data, findi…
Spiral Inflation with Coleman-Weinberg Potential
2015
We apply the idea of spiral inflation to Coleman-Weinberg potential, and show that inflation matching well observations is allowed for a symmetry-breaking scale ranging from an intermediate scale to GUT scale even if the quartic coupling $\lambda$ is of $\mathcal{O}(0.1)$. The tensor-to-scalar ratio can be of $\mathcal{O}(0.01)$ in case of GUT scale symmetry-breaking.
Spontaneous baryogenesis in spiral inflation
2019
We examined the possibility of spontaneous baryogenesis driven by the inflaton in the scenario of spiral inflation, and found the parametric dependence of the late-time baryon number asymmetry. As a result, it is shown that, depending on the effective coupling of baryon/lepton number violating operators, it is possible to obtain the right amount of asymmetry even in the presence of a matter-domination era as long as such era is relatively short. In a part of the parameter space, the required expansion rate during inflation is close to the current upper-bound, and hence can be probed in the near future experiments.