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Yeo-Yie Charng

Publications and source records attributed to Yeo-Yie Charng.

13 recordsLinked to original sources
arXiv2011

Photon production from non-equilibrium disoriented chiral condensates in a longitudinal expansion : A theoretic framework

A theoretical framework is developed for treating the quantization of the photons in a spacetime with a longitudinal expansion. This can be used to study the production of the photons through the non-equilibrium relaxation of a disoriented chiral condensate presumably formed in the expanding hot central region in ultra-relativistic heavy-ion collisions. These photons can be a signature of the formation of disoriented chiral condensates in the direct photon measurements of heavy-ion collisions.

hep-ph↗
arXiv2009

Affleck-Dine Baryogenesis, Split Supersymmetry, and Inflation

It is shown that, in the context of split supersymmetry, a simple model with a single complex scalar field can produce chaotic inflation and generate the observed amount of baryon asymmetry via the Affleck-Dine mechanism. While the inflaton quantum fluctuations give rise to curvature perturbation, we show that quantum fluctuations of the phase of the scalar field can produce baryonic isocurvature perturbation. Combining with constraints from WMAP data, all parameters in the model can be determined to within a narrow range.

hep-ph↗
arXiv2008

Okubo-Zweig-Iizuka-rule violation and B\to η^{(\prime)}K branching ratios

We show that few-percent Okubo-Zweig-Iizuka-rule violating effects in the quark-flavor basis for the $η$-$η'$ mixing can enhance the chiral scale associated with the $η_q$ meson few times. This enhancement is sufficient for accommodating the dramatically different data of the $B\toη^{\prime} K$ and $B\toηK$ branching ratios. We comment on other proposals for resolving this problem, including flavor-singlet contributions, axial U(1) anomaly, and nonperturbative charming penguins. Discrimination of the above proposals by means of the $B\toη^{(\prime)}\ellν$ and $B_s\toη^{(\prime)}\ell\ell$ data is suggested.

hep-ph↗
arXiv2007

Quantum noise and large-scale cosmic microwave background anisotropy

We propose a new source for the cosmological density perturbation which is passive fluctuations of the inflaton driven dynamically by a colored quantum noise as a result of its coupling to other massive quantum fields. The created fluctuations grow with time during inflation before horizon-crossing. However, the larger-scale modes cross out the horizon earlier, thus resulting in a suppression of their density perturbation as compared with those on small scales. By using current observed CMB data to constrain the parameters introudced, we find that a significant contribution from the noise-driven perturbation to the density perturbation is still allowed. It in turn gives rise to a suppression of the large-scale CMB anisotropy that may be relevant to the observed low quadrupole in the WMAP CMB anisotropy data. We also briefly discuss the implications to the energy scale of inflation and the spectral index and non-Gaussianity of the density perturbation.

astro-ph↗
arXiv2007

Gluonic contribution to $B\to η^{(\prime)}$ form factors

We calculate the flavor-singlet contribution to the $B\toη^{(\prime)}$ transition form factors from the gluonic content of the $η^{(\prime)}$ meson in the large-recoil region using the perturbative QCD approach. The formulation for the $η$-$η'$ mixing in the quark-flavor and singlet-octet schemes is compared, and employed to determine the chiral enhancement scales associated with the two-parton twist-3 $η^{(\prime)}$ meson distribution amplitudes. It is found that the gluonic contribution is negligible in the $B\toη$ form factors, and reaches few percents in the $B\toη'$ ones. Its impact on the accommodation of the measured $B\toη^{(\prime)} K$ branching ratios in the perturbative QCD and QCD-improved factorization approaches is elaborated.

hep-ph↗
arXiv2005

Nonequilibrium Effects and Baryogenesis

Possible effects due to nonequilibrium dynamics in the Affleck-Dine mechanism of baryogenesis are examined. Using the closed-time-path formalism, the quantum fluctuation and the back reaction of the Affleck-Dine scalar field are incorporated self-consistently into the dynamical equations of the system. It is found that such nonequilibrium effects can significantly affect the amount of baryon asymmetry that can be generated. In particular, it is possible to generate the observed baryon asymmetry with suitable initial conditions. The methodology described in this paper as well as some of the results obtained are quite general, and can be applied to any complex scalar field in a cosmological background.

hep-ph↗
arXiv2005

B meson wave function from the $B\toγlν$ decay

We show that the leading-power $B$ meson wave function can be extracted reliably from the photon energy spectrum of the $B\toγlν$ decay up to $O(1/m_b^2)$ and $O(α_s^2)$ uncertainty, $m_b$ being the $b$ quark mass and $α_s$ the strong coupling constant. The $O(1/m_b)$ corrections from heavy-quark expansion can be absorbed into a redefined leading-power $B$ meson wave function. The two-parton $O(1/m_b)$ corrections cancel exactly, and the three-parton $B$ meson wave functions turn out to contribute at $O(1/m_b^2)$. The constructive long-distance contribution through the $B\to V\toγ$ transition, $V$ being a vector meson, almost cancels the destructive $O(α_s)$ radiative correction. Using models of the leading-power $B$ meson wave function available in the literature, we obtain the photon energy spectrum in the perturbative QCD framework, which is then compared with those from other approaches.

hep-ph↗
arXiv2005

Weak phases from the $B\to ππ$, $Kπ$ decays

Recent data of two-body nonleptonic $B$ meson decays allow a topological-amplitude analysis up to the $O(λ^2)$ accuracy, where $λ$ denotes the Wolfenstein parameter. We find a solution from the $B\toππ$ data and a solution from the $B\to Kπ$ data, which satisfy the approximate SU(3) flavor symmetry. These solutions indicate that the color-suppressed tree amplitude is large, all other amplitudes can be understood within the standard model, and the weak phases $ϕ_2\approx 90^o$ and $ϕ_3\approx 60^o$ are consistent with the global unitarity triangle fit.

hep-ph↗
arXiv2004

Weak phases from topological-amplitude parametrization

We propose a parametrization for two-body nonleptonic $B$ meson decays, in which the various topologies of amplitudes are counted in terms of powers of the Wolfenstein parameter $λ\sim 0.22$. The weak phases and the amplitudes are determined by comparing this parametrization with available measurements. It is possible to obtain the phase $ϕ_3$ from the $B\to Kπ$ data up to theoretical uncertainty of $O(λ^3)\sim 1%$. The recently measured $B_d^0\toπ^0π^0$ branching ratio implies a large color-suppressed or penguin amplitude, and that the extraction of the phase $ϕ_2$ from the $B\toππ$ data may suffer theoretical uncertainty more than the expected one of $O(λ^2)\sim 5%$.

hep-ph↗
arXiv2004

Off-equilibrium dynamics of the primordial perturbations in the inflationary universe: the O(N) model

Using the O(N) model as an example, we investigate the self-interaction effects of inflaton on the dynamics of the primordial perturbations. When taking interactions into account, it is essential to employ a self-consistent off-equilibrium formalism to study the evolution of the inflationary background field and its fluctuations with the back-reaction effects. Within the Hartree factorization scheme, we show that the O(N) model has at least two observable remains left behind the off-equilibrium processes: the running spectral index of primordial density perturbations and the correlations between perturbation modes in phase space. We find that the running of the spectral index is fully determined by the rate of the energy transfer from the inflationary background field to its fluctuations via particle creation processes as well as the dynamics of the background field itself. Furthermore, the amplitude of the field fluctuations turns out to be scale-dependent due to the off-equilibrium evolution. As a consequence, the scale-dependence of fluctuations yields a correlation between the phase space modes of energy density perturbations, while the one-point function of the fluctuations in each Hartree mode is still Gaussian. More importantly, the mode-mode correlation of the primordial perturbations depends upon the dynamics of the self-interaction {\it as well as} the initial conditions of the inflation. Hence, we propose that the running spectral index and the correlation between phase-space modes would be two observable fossils to probe the epoch of inflation, even beyond.

astro-ph↗
arXiv2004

Running spectral index and mode-mode correlation of inflationary perturbations from off-equilibrium effects

We study the off-equilibrium effects of inflaton on the dynamics of primordial perturbations in the O(N) model. A self-consistent off-equilibrium formalism is employed to investigate the evolution of the inflationary background field and its fluctuations with the back-reaction effects. We find two observable remains left behind the off-equilibrium processes: the running spectral index of primordial density perturbations and the correlations between perturbation modes in phase space, which would serve as the imprints to probe the epoch of inflation, even beyond.

astro-ph↗
arXiv2002

Photon Production from Nonequilibrium Disoriented Chiral Condensates in a Spherical Expansion

We study the production of photons through the non-equilibrium relaxation of a disoriented chiral condensate formed in the expanding hot central region in ultra-relativistic heavy-ion collisions. It is found that the expansion smoothes out the resonances in the process of parametric amplification such that the non-equilibrium photons are dominant to the thermal photons over the range 0.2-2 GeV. We propose that to search for non-equilibrium photons in the direct photon measurements of heavy-ion collisions can be a potential test of the formation of disoriented chiral condensates.

hep-ph↗
arXiv2001

Nonperturbative Lattice Simulation of High Multiplicity Cross Section Bound in $ϕ^4_3$ on Beowulf Supercomputer

In this thesis, we have investigated the possibility of large cross sections at large multiplicity in weakly coupled three dimensional $ϕ^4$ theory using Monte Carlo Simulation methods. We have built a Beowulf Supercomputer for this purpose. We use spectral function sum rules to derive a bound on the total cross section where the quantity determining the bound can be measured by Monte Carlo simulation in Euclidean space. We determine the critical threshold energy for large high multiplicity cross section according to the analysis of M.B. Volosion and E.N. Argyres, R.M.P. Kleiss, and C.G. Papadopoulos. We compare the simulation results with the perturbation results and see no evidence for large cross section in the range where tree diagram estimates suggest they should exist.

hep-lat↗