arXiv subjects

P. Ko

Publications and source records attributed to P. Ko.

At least 127 records · Page 7Linked to original sources

arXiv2005

Direct detection of neutralino dark matter in supergravity

The direct detection of neutralino dark matter is analysed in general supergravity scenarios, where non-universal soft scalar and gaugino masses can be present. In particular, the theoretical predictions for the neutralino-nucleon cross section are studied and compared with the sensitivity of dark matter detectors. We take into account the most recent astrophysical and experimental constraints on the parameter space, including the current limit on B(Bs-> mu+ mu-). The latter puts severe limitations on the dark matter scattering cross section, ruling out most of the regions that would be within the reach of present experiments. We show how this constraint can be softened with the help of appropriate choices of non-universal parameters which increase the Higgsino composition of the lightest neutralino and minimise the chargino contribution to the b->s transition.

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arXiv2005

The Discovery Potential of a Super B Factory

The Proceedings of the 2003 SLAC Workshops on flavor physics with a high luminosity asymmetric e+e- collider. The sensitivity of flavor physics to physics beyond the Standard Model is addressed in detail, in the context of the improvement of experimental measurements and theoretical calculations.

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arXiv2005

Neutralino dark matter scattering and $B_s \to μ^+ μ^-$ in SUSY models

It is pointed out that there is a strong correlation between the neutralino dark matter scattering cross section $σ_{\tildeχ p}$ and the branching ratio for $B_s \to μ^+ μ^-$ within minimal supergravity (mSUGRA) and its extensions. This correlation arises mainly from $\tanβ$ and heavy neutral Higgs mass dependence, and shows a nice interplay between vastly different two observables within supersymmetric models. Current upper limit on $B(B_s \to μ^+ μ^-) < 5.8 \times 10^{-7}$ excludes substantial parameter space where $σ_{\tildeχ p}$ is within the CDMS sensitivity region.

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arXiv2005

Supersymmetry, flavor physics and dark matter

In this talk, I first discuss $b\to d$, $b\to s$ and $s\to d$ transitions including time-dependent CP asymmetries in $B_d \to ϕK_s$ and Re ($ε^{'}/ε_K$). Then I show that the decay $B_s \to μ^+ μ^-$ is useful to distinguish various SUSY breaking mechanisms. I will also describe some possible connections between B physics and cosmology: (i) B physics and electroweak baryogenesis within SUSY models, and (ii) the correlation between the neutralino dark matter scattering and $B (B_s \to μ^+ μ^-)$. In particular, we point out that the current upper bound on $B (B_s \to μ^+ μ^-)$ form CDF and D0 collaborations can constrain the spin-independent neutralino scattering cross section more strongly than the CDMS bound.

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arXiv2005

B physics and Supersymmetry

In SUSY models, it is still possible to have large signals even if the current data on $K$ and $B$ systems are consistent with the CKM paradigm for flavor mixing and CP violation. I first discuss $b\to d$ and $b\to s$ transitions including time-dependent CP asymmetries in $B_d \to ϕK_s$, and usefulness of $B_s \to μ^+ μ^-$ to distinguish various SUSY breaking mechanisms. Then I will discuss some possible connections between B physics and cosmology: (i) B physics and electroweak baryogenesis within SUSY models, and (ii) the correlation between the neutralino dark matter scattering and $B (B_s \to μ^+ μ^-)$.

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arXiv2005

Dipion invariant mass spectrum in $X(3872) \to J/ψππ$

It is pointed out that dipion invariant mass spectrum in $X (3872) \to ππJ/ψ$ is a useful probe for the $J^{PC}$ quantum number of the X(3872), complementary to the angular distributions. If X(3872) is a $^1 P_1$ state, the dipion has a peak at low $m_{ππ}$ region, which is not in accord with the preliminary Belle data. If X(3872) is a $^3 D_2$ or $^3 D_3$ state, the dipion spectrum shows a peak at high $m_{ππ}$ region, which is broader than the $ρ$ resonance that might come from the decay of a molecular state: $(D \bar{D^*}) (I=1) \to J/ψρ\to J/ψπ^+ π^-$. Better measurement of $m_{ππ}$ spectrum will shed light on the nature of X(3872).

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arXiv2003

Chiral perturbation theory for pentaquark baryons and its applications

We construct a chiral lagrangian for pentaquark baryons assuming that the recently found Theta^+ (1540) state belongs to an antidecuplet of SU(3) flavor symmetry with J^P = (1/2)^(+-). We derive the Gell-Mann-Okubo formulae for the antidecuplet baryon masses, and a possible mixing between the antidecuplet and the pentaquark octet. Then we calculate the cross sections for pi^- p -> K^- Theta^+ and gamma n -> K^- Theta^+ using our chiral lagrangian. The resulting amplitudes respect the underlying chiral symmetry of QCD correctly. We also describe how to include the light vector mesons in the chiral lagrangian.

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arXiv2003

B --> Phi K_S and Supersymmetry

The rare decay B --> Phi K_S is a well-known probe of physics beyond the Standard Model because it arises only through loop effects yet has the same time-dependent CP asymmetry as B --> Psi K_S. Motivated by recent data suggesting new physics in B --> Phi K_S, we look to supersymmetry for possible explanations, including contributions mediated by gluino loops and by Higgs bosons. Chirality-preserving LL and RR gluino contributions are generically small, unless gluinos and squarks masses are close to the current lower bounds. Higgs contributions are also too small to explain a large asymmetry if we impose the current upper limit on B(B_s --> mu mu). On the other hand, chirality-flipping LR and RL gluino contributions can provide sizable effects and while remaining consistent with related results in B --> Psi K_S, Delta M_s, B --> X_s gamma and other processes. We discuss how the LR and RL insertions can be distinguished using other observables, and we provide a string-based model and other estimates to show that the needed sizes of mass insertions are reasonable.

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arXiv2003

B(d) --> phi K(S) CP asymmetries as an important probe of supersymmetry

The decay $B_d \to ϕK_S$ is a special probe of physics beyond the Standard Model (SM), since it has no SM tree level contribution. Motivated by recent data suggesting a deviation from the SM for its time-dependent CP asymmetry, we examine supersymmetric explanations. Chirality preserving contributions are generically small, unless gluino is relatively light. Higgs contributions are also too small to explain a large asymmetry. Chirality flipping $LR$ and $RL$ gluino contributions actually can provide sizable effects without conflict with all related results. We discuss how various insertions can be distinguished, and argue the needed sizes of mass insertions are reasonable.

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arXiv2003

SUSY breaking mediation mechanisms and (g-2)_μ, B -> X_s γ, B -> X_{s} l^+ l^- and B_s -> μ^+ μ^-

We show that there are qualitative differences in correlations among $(g-2)_μ$, $B\to X_s γ$, $B \to X_{s} l^+ l^-$ and $B_s \to μ^+ μ^-$ in various SUSY breaking mediation mechanisms: minimal supergravity (mSUGRA), gauge mediation (GMSB), anomaly mediation (AMSB), gaugino mediation ($\tilde{g}$MSB), weakly and strongly interacting string theories, and $D$ brane models. After imposing the direct search limits on the Higgs boson and SUSY particle search limits and $B\to X_s γ$ branching ratio, we find all the scenarios can accommodate the $a_μ\equiv (g-2)_μ/2 $ in the range of (a few tens)$\times 10^{-10}$, and predict that the branching ratio for $B\to X_s l^+ l^-$ can differ from the standard model (SM) prediction by $\pm 20 %$ but no more. On the other hand, the $B_s \to μ^+ μ^-$ is sensitive to the SUSY breaking mediation mechanisms through the pseudoscalar and stop masses ($m_A$ and $m_{\tilde{t}_1}$), and the stop mixing angle. In the GMSB with a small messenger number, the AMSB, the $\tilde{g}$MSB and the noscale scenarios, one finds that $B(B_s \to μ^+ μ^-) \lesssim 2 \times 10^{-8}$, which is below the search limit at the Tevatron Run II. Only the mSUGRA or string inspired models can generate a large branching ratio for this decay.

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arXiv2003

Implications on SUSY breaking mediation mechanisms from observing $B_s \to μ^+ μ^-$ and the muon $(g-2)$

We consider $B_s \to μ^+ μ^-$ and the muon $(g-2)_μ$ in various SUSY breaking mediation mechanisms. If the decay $B_s \to μ^+ μ^-$ is observed at Tevatron Run II with a branching ratio larger than $\sim 2 \times 10^{-8} $, the noscale supergravity (including the gaugino mediation), the gauge mediation scenario with small number of messenger fields and low messenger scale, and a class of anomaly mediation scenarios will be excluded, even if they can accommodate a large muon $(g-2)_μ$. On the other hand, the minimal supergravity scenario and similar mechanisms derived from string models can accommodate this observation.

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arXiv2002

B-decays at Large $\tanβ$ as a Probe of SUSY Breaking

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arXiv2002

CP violations in the K and B meson systems in the SUSY models with (S_3)^3 flavor symmetry

Rare decays of B and K mesons and CP violations thereof are considered in SUSY models with S_3^3 flavor symmetry. SUSY contributions to epsilon_K and epsilon'/epsilon_K can be large, but not to B0 - B0 bar mixing because of strong constraint from B -> X_d gamma for (delta^d_{13})_{LR}. Still large deviations from the SM predictions are possible in the branching ratio for B -> X_d gamma and direct CP violations therein, even if the KM angle gamma is in the range preferred by the SM CKM fit. Experimental study of B -> X_d gamma is strongly recommended as a probe for new physics with nontrivial flavor structure in the (13) mixing.

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arXiv2002

B0 - B0 bar mixing, B -> J/psi K_S and B -> X_d gamma in general MSSM

We consider the gluino-mediated SUSY contributions to B0 - B0 bar mixing, B -> J/psi K_S and B -> X_d gamma in the mass insertion approximation. We find the LL mixing parameter can be as large as |delta_{13}^d_{LL}| < 2*10^-1, but the LR mixing is strongly constrained by the B -> X_d gamma branching ratio and we find |delta_{13}^d_{LR}| < 10^-2. The implications for the direct CP asymmetry in B -> X_d gamma and the dilepton charge asymmetry (A_{ll}) are also discussed, where substantial deviations from the standard model predictions are possible.

hep-ph↗

arXiv2002

CP--violating Chargino Contributions to the Higgs Coupling to Photon Pairs in the Decoupling Regime of Higgs Sector

In most supersymmetric theories, charginos $\tildeχ^\pm_{1,2}$ belong to the class of the lightest supersymmetric particles and the couplings of Higgs bosons to charginos are in general complex so that the CP--violating chargino contributions to the loop--induced coupling of the lightest Higgs boson to photon pairs can be sizable even in the decoupling limit of large pseudoscalar mass $m_A$ with only the lightest Higgs boson kinematically accessible at future high energy colliders. We introduce a specific benchmark scenario of CP violation consistent with the electric dipole moment constraints and with a commonly accepted baryogenesis mechanism in the minimal supersymmetric Standard Model. Based on the benchmark scenario of CP violation, we demonstrate that the fusion of the lightest Higgs boson in linearly polarized photon--photon collisions can allow us to confirm the existence of the CP--violating chargino contributions {\it even in the decoupling regime of the Higgs sector} for nearly degenerate SU(2) gaugino and higgsino mass parameters of about the electroweak scale.

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arXiv2002

MSSM Higgs sector CP violation at photon colliders: Revisited

We present a comprehensive analysis on the MSSM Higgs sector CP violation at photon colliders including the chargino contributions as well as the contributions of other charged particles. The chargino loop contributions can be important for the would-be CP odd Higgs production at photon colliders. Polarization asymmetries are indispensable in determining the CP properties of neutral Higgs bosons.

hep-ph↗

arXiv2002

Muon anomalous magnetic moment from effective supersymmetry

We present a detailed analysis on the possible maximal value of the muon (g-2) (= 2 a_mu) within the context of effective SUSY models with R parity conservation. First of all, the mixing among the second and the third family sleptons can contribute at one loop level to the a_mu(SUSY) and tau -> mu gamma simultaneously. One finds that the a_mu(SUSY) can be as large as (10-20)*10^-10 for any tan beta, imposing the upper limit on the tau -> mu gamma branching ratio. Furthermore, the two-loop Barr-Zee type contributions to a_mu(SUSY) can be significant for large tan beta, if a stop is light and mu and A_t are large enough (O(1) TeV). In this case, it is possible to have a_mu(SUSY) upto O(10)*10^-10 without conflicting with tau -> l gamma. We conclude that the possible maximal value for a_mu(SUSY) is about 20*10^-10 for any tan beta. Therefore the BNL experiment on the muon a_mu can exclude the effective SUSY models only if the measured deviation is larger than \sim 30*10^-10.

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arXiv2001

Muon anomalous magnetic moment, $B\to X_s γ$ and dark matter detection in the string models with dilaton domination

We consider the muon anomalous magnetic moment $a_μ$ in the string models with dilaton domination with two different string scales : the usual GUT scale and the intermediate scale. After imposing the direct search limits on the lightest neutral Higgs and SUSY particle masses and the lightest neutralino LSP, the $a_μ^{\rm SUSY}$ is predicted to be less than $65 (55) \times 10^{-10}$ for $M_{string} = 2 \times 10^{16}$ GeV ($3 \times 10^{11}$ GeV). If we further impose the $B\to X_s γ$ branching ratio, the predicted $a_μ^{\rm SUSY}$ becomes lower to $35 \times 10^{-10}$ for intermediate string scale. The resulting LSP - proton scattering cross section is less than $\sim 10^{-7}$ pb, which is below the sensitivity of the current direct dark matter search experiments, but could be covered by future experiments.

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