arXiv subjects

Cheng-Wei Chiang

Publications and source records attributed to Cheng-Wei Chiang.

At least 181 records · Page 10Linked to original sources

arXiv2006

A minimal supersymmetric scenario with only μat the weak scale

Inspired by split supersymmetry, we study a minimal supersymmetric scenario with only the Higgsino mass parameter $μ$ below the TeV scale. The motivation is to satisfy the gauge coupling unification and dark matter constraints with the minimal particle contents at the electroweak scale in supersymmetric models. With the neutral Higgsino as the lightest supersymmetric particle, we discuss the dark matter signals in both direct and indirect detection. We also discuss collider phenomenology associated with the two lightest neutralinos and the lightest chargino, which are almost degenerate in mass even after taking into account radiative corrections. Unfortunately, the collider signals may be very difficult for identifying such a scenario because the pions or leptons in the final state are too soft.

hep-ph↗

arXiv2005

Constraining gamma from K* pi and rho K Decays

We show that information on the weak phase gamma can be extracted from the K* pi and rho K decays. Less hadronic uncertainty is involved when the observables of four of these modes are combined together. We further point out two approximate relations in these decay modes can help determine whether there are new physics contributions in Delta I = 1 transitions, as hinted in the K pi modes.

hep-ph↗

arXiv2005

Splitting the split supersymmetry

In split supersymmetry, the supersymmetric scalar particles are all very heavy, at least at the order of 10^9 GeV, but the gauginos, Higgsinos, and one of the neutral Higgs bosons remain below a TeV. Here we further split the split supersymmetry by taking the Higgsino mass parameter μto be very large. In this case, the μproblem is avoided and we keep the wino as a dark matter candidate. A crude gauge coupling unification is still preserved. Dark matter signals and collider phenomenology are discussed in this μ-split SUSY scenario. The most interesting dark matter signal is the annihilation into monochromatic photons. In colliders, chargino-pair and the associated chargino-neutralino production cross sections have a certain ratio due to gauge couplings, and the chargino has long decays.

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arXiv2004

Axion Models with High-Scale Supersymmetry Breaking

Inspired by the possibility of high-scale supersymmetry breaking in the string landscape where the cosmological constant problem and the gauge hierarchy problem can be solved while the strong CP problem is still a challenge for naturalness, we propose a supersymmetric KSVZ axion model with an approximate universal intermediate-scale ($\sim 10^{11}$ GeV) supersymmetry breaking. To protect the global Peccei--Quinn (PQ) symmetry against quantum gravitational violation, we consider the gauged discrete $Z_N$ PQ symmetry. In our model the axion can be a cold dark matter candidate, and the intermediate supersymmetry breaking scale is directly related to the PQ symmetry breaking scale. Gauge coupling unification can be achieved at about $2.7\times 10^{16}$ GeV. The Higgs mass range is 130 GeV to 160 GeV. We briefly discuss other axion models with high-scale supersymmetry breaking where the stabilization of the axion solution is similar.

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arXiv2004

Solution to the B -> pi K Puzzle in a Flavor-Changing Z' Model

Recent experiments suggest that certain B -> pi K branching ratios are inconsistent with the standard model expectations. We show that a flavor-changing Z' provides a solution to the problem. Electroweak penguin amplitudes are enhanced by the Z' boson for select parameters. We discuss implications for the Z' mass and its couplings to the standard model fermions. We also show that the solution is consistent with constraints from the CP asymmetries of the B -> phi K_S decay.

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arXiv2004

B_s-anti-B_s Mixing in Z' Models with Flavor-Changing Neutral Currents

In models with an extra U(1)' gauge boson family non-universal couplings to the weak eigenstates of the standard model fermions generally induce flavor-changing neutral currents. This phenomenon leads to interesting results in various B meson decays, for which recent data indicate hints of new physics involving significant contributions from b -> s transitions. We analyze the B_s system, emphasizing the effects of a Z' on the mass difference and CP asymmetries.

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arXiv2004

Charmless $B \to PP$ decays using flavor SU(3) symmetry

The decays of $B$ mesons to a pair of charmless pseudoscalar ($P$) mesons are analyzed within a framework of flavor SU(3). Symmetry breaking is taken into account in tree ($T$) amplitudes through ratios of decay constants; exact SU(3) is assumed elsewhere. Acceptable fits to $B \to ππ$ and $B \to K π$ branching ratios and CP asymmetries are obtained with tree, color-suppressed ($C$), penguin ($P$), and electroweak penguin ($P_{EW}$) amplitudes. Crucial additional terms for describing processes involving $η$ and $η'$ include a large flavor-singlet penguin amplitude ($S$) as proposed earlier and a penguin amplitude $P_{tu}$ associated with intermediate $t$ and $u$ quarks. For the $B^+ \to π^+ η'$ mode a term $S_{tu}$ associated with intermediate $t$ and $u$ quarks also may be needed. Values of the weak phase $γ$ are obtained consistent with an earlier analysis of $B \to VP$ decays, where $V$ denotes a vector meson, and with other analyses of CKM parameters.

hep-ph↗

arXiv2003

Z' Mediated Flavor Changing Neutral Currents in B Meson Decays

We study the effects of an extra U(1)' gauge boson with flavor changing couplings with fermion mass eigenstates on certain B meson decays that are sensitive to such new physics contributions. In particular, we examine to what extent the current data on B_d -> ϕK, B_d -> η' K and B_s -> μ^+ μ^- decays may be explained in such models, concentrating on the example in which the flavor changing couplings are left-chiral. We find that within reasonable ranges of parameters, the Z' contribution can readily account for the anomaly in S_{ϕK_S} but is not sufficient to explain large branching ratio of B_d -> η' K with the same parameter value. S_{ϕK_S} and S_{η' K_S} are seen to be the dominant observables that constrain the extra weak phase in the model.

hep-ph↗

arXiv2003

Charmless $B \to VP$ Decays Using Flavor SU(3) Symmetry

The decays of $B$ mesons to a charmless vector ($V$) and pseudoscalar ($P$) meson are analyzed within a framework of flavor SU(3) in which symmetry breaking is taken into account through ratios of decay constants in tree ($T$) amplitudes. The magnitudes and relative phases of tree and penguin amplitudes are extracted from data; the symmetry assumption is tested; and predictions are made for rates and CP asymmetries in as-yet-unseen decay modes. A key assumption for which we perform some tests and suggest others is a relation between penguin amplitudes in which the spectator quark is incorporated into either a pseudoscalar meson or a vector meson. Values of $γ$ slightly restricting the range currently allowed by fits to other data are favored, but outside this range there remain acceptable solutions which cannot be excluded solely on the basis of present $B \to VP$ experiments.

hep-ph↗

arXiv2003

Two-Body Charmless B Decays Involving eta and eta'

We discuss implications of recent experimental data for B decays into two pseudoscalar mesons, with emphasis on those with $η$ and $η'$ in the final states. Applying a U-spin argument, we show that tree and penguin amplitudes, both in $B^+ \to π^+ η$ and in $B^+ \to π^+ η'$, are of comparable magnitudes. Nontrivial relative weak and strong phases between the tree-level amplitudes and penguin-loop amplitudes in the $B^{\pm} \to π^{\pm} η$ modes are extracted. We predict possible values for the averaged branching ratio and CP asymmetry of the $B^{\pm} \to π^{\pm} η'$ modes. We test the assumption of a singlet-penguin amplitude with the same weak and strong phases as the QCD penguin in explaining the large branching ratios of $η' K$ modes, and show that it is consistent with current branching ratio and CP asymmetry data of the $B^+ \to (π^0, η, η') K^+$ modes. We also show that the strong phases of the singlet-penguin and tree-level amplitudes can be extracted with further input of electroweak penguin contributions and a sufficiently well-known branching ratio of the $ηK^+$ mode. Using SU(3) flavor symmetry, we also estimate required data samples to detect modes that have not yet been seen.

hep-ph↗

arXiv2003

New Physics Contributions to The B -> phi K_S Decay

Recent measurements of the time-dependent CP asymmetry of the B -> phi K_S decay give results whose central values differ from standard model expectations. It is shown how such data can be used to identify new physics contributions in a model-independent manner. In general, a sizeable new amplitude with nontrivial weak and strong phases would be required to explain current data. Improvement in the quality of data will allow one to form a more definite conclusion.

hep-ph↗

arXiv2003

Final-State Phases in $B \to D π, D^* π$, and $D ρ$ Decays

The final-state phases in $\bar{B} \to D π, D^* π$, and $D ρ$ decays appear to follow a pattern similar to those in $D \to \bar{K} π$, $\bar{K}^* π$, and $\bar{K} ρ$ decays. Each set of processes is characterized by three charge states but only two independent amplitudes, so the amplitudes form triangles in the complex plane. For the first two sets the triangles appear to have non-zero area, while for the $D ρ$ or $\bar{K} ρ$ decays the areas of the triangles are consistent with zero. Following an earlier discussion of this behavior for $D$ decays, a similar analysis is performed for B decays, and the relative phases and magnitudes of contributing amplitudes are determined. The significance of recent results on $\ob \to D^{(*)0} \bar{K}^{(*)0}$ is noted. Open theoretical and experimental questions are indicated.

hep-ph↗

arXiv2002

Light Gluino and the Running of alpha_s

A gluino in the mass range 12--16 GeV combined with a light (2--5.5 GeV) bottom squark, as has been proposed recently to explain an excess of b quark hadroproduction, would affect the momentum-scale dependence (``running'') of the strong coupling constant alpha_s in such a way as to raise its value at M_Z by about 0.014 +/- 0.001. If one combines sources of uncertainty at low (m_b) and high (M_Z) mass scales, one can only distinguish such an effect at slightly more than the 2 sigma level. Prospects for improvement in this situation, which include better lattice QCD simulations and better measurements at M_Z, are discussed.

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arXiv2002

Two-Body Cabibbo-Suppressed Charmed Meson Decays

Singly-Cabibbo-suppressed decays of charmed particles governed by the quark subprocesses $c \to s u \bar s$ and $c \to d u \bar d$ are analyzed using a flavor-topology approach, based on a previous analysis of the Cabibbo-favored decays governed by $c \to s u \bar d$. Decays to $PP$ and $PV$, where $P$ is a pseudoscalar meson and $V$ is a vector meson, are considered. We include processes in which $η$ and $η'$ are produced.

hep-ph↗

arXiv2002

$B \to D_s π$ and the tree amplitude in $B \to π^+ π^-$

The recently-observed decay $B^0 \to D_s^+ π^-$ is expected to proceed mainly by means of a tree amplitude in the factorization limit: $B^0 \to π^- {(W^+)}^*$, ${(W^+)}^* \to D_s^+$. Under this assumption, we predict the corresponding contribution of the tree amplitude to $B^0 \to π^+ π^-$. We indicate the needed improvements in data that will allow a useful estimate of this amplitude with errors comparable to those accompanying other methods. Since the factorization hypothesis for this process goes beyond that proved in most approaches, we also discuss independent tests of this hypothesis.

hep-ph↗

arXiv2002

Higgs Boson Decay into Hadronic Jets

The remarkable agreement of electroweak data with standard model (SM) predictions motivates the study of extensions of the SM in which the Higgs boson is light and couples in a standard way to the weak gauge bosons. Postulated new light particles should have small couplings to the gauge bosons. Within this context it is natural to assume that the branching fractions of the light SM-like Higgs boson mimic those in the standard model. This assumption may be unwarranted, however, if there are non-standard light particles coupled weakly to the gauge bosons but strongly to the Higgs field. In particular, the Higgs boson may effectively decay into hadronic jets, possibly without important bottom or charm flavor content. As an example, we present a simple extension of the SM, in which the predominant decay of the Higgs boson occurs into a pair of light bottom squarks that, in turn, manifest themselves as hadronic jets. Discovery of the Higgs boson remains possible at an electron-positron linear collider, but prospects at hadron colliders are diminished substantially.

hep-ph↗

arXiv2001

Updated Analysis of Some Two-Body Charmless B Decays

New data from the BaBar, Belle, and CLEO Collaborations on B decays to two-body charmless final states are analyzed, with the following consequences: (1) The penguin amplitude which dominates the decay $B^+ \to π^+ K^{*0}$ has a magnitude similar to that dominating $B^+ \to π^+ K^0$. (2) The decay $B^+ \to π^+ η$, a good candidate for observing direct CP violation, should be detectable at present levels of sensitivity. (3) The decays $B^+ \to η' K^+$ and $B^+ \to ηK^{*+}$ are sufficiently similar in rate to the corresponding decays $B^0 \to η' K^0$ and $B^0 \to ηK^{*0}$, respectively, that one cannot yet infer the need for ``tree'' amplitudes $t'$ contributing to the $B^+$ but not the $B^0$ decays. Statistical requirements for observing this and other examples of tree-penguin interference are given. (4) Whereas the $B^+ \to η' K^+$ and $B^0 \to η' K^0$ rates cannot be accounted for by the penguin amplitude $p'$ alone but require an additional flavor-singlet penguin contribution $s'$, no such flavor-singlet penguin contribution is yet called for in the decays $B^+ \to ηK^{*+}$ or $B^0 \to ηK^{*0}$. Predictions for the rates for $B^+ \to η' K^{*+}$ and $B^0 \to η' K^{*0}$ are given which would allow one to gauge the importance of these flavor-singlet penguin amplitudes.

hep-ph↗

arXiv2001

Final-State Phases in Doubly-Cabibbo-Suppressed Charmed Meson Nonleptonic Decays

Cabibbo-favored nonleptonic charmed particle decays exhibit large final-state phase differences in $\bar K π$ and $\bar K^* π$ but not $\bar K ρ$ channels. It is of interest to know the corresponding pattern of final-state phases in doubly-Cabibbo-suppressed decays, governed by the $c \to d u \bar s$ subprocess. An experimental program is outlined for determining such phases via measurements of rates for $D \to K^* π$ and $K (ρ, ω,ϕ)$ channels, and determination of interference between bands in Dalitz plots. Such a program is feasible at planned high-intensity sources of charmed particles.

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