Bounds on warped extra dimensions from a Standard Model-like Higgs boson

We point out that the discovery of a light Higgs boson in the γγ, ZZ, and WW   decay channels at the LHC, with cross sections not far from the predictions of the Standard Model, would have profound implications for the parameters of warped extra-dimension models with a brane-localized Higgs sector. Due to loop effects of Kaluza–Klein particles, these models predict a significant reduction of the Higgs production cross section via gluon–gluon fusion, combined with an enhancement of the ratio Br(h→γγ)/Br(h→ZZ)$\mathrm{Br}(h\to \gamma \gamma )/\mathrm{Br}(h\to ZZ)$ in large parts of parameter space. LHC measurements of these decays will probe Kaluza–Klein masses up to the 10 TeV range, exceeding by far the reach for direct production.     

Enhanced production of TeV right-handed neutrinos through the large magnetic moment

We examine the effects of magnetic moments of right-handed neutrinos, whose masses are set at around TeV scale, then it is plausible to have a large enhancement for the production cross section of TeV scale right-handed neutrinos though the Drell–Yan process, e⁺e⁻→γ$e^{+}{e}^{-}\to \gamma$, Z^∗→NiNj$Z^{\ast }\to N_i{N}_j$(i≠j)$(i\ne j)$, which is within the reach of the future linear collider (ILC).     

Anomalous Higgs couplings at the LHeC

The discovery of Higgs boson plays a crucial role in understanding the electroweak symmetry breaking sector. From now on, solving the dynamics of this sector needs precision measurements of the couplings of the Higgs boson to the Standard Model particles. In this work, we investigate the constrains on the anomalous HWW   and HWWγ$HWW\gamma$ couplings, described by the dimension-six operators in the effective Lagrangian, in a high energy envisaged ep collider which is called Large Hadron electron Collider (LHeC). We obtained the 95% confidence level limits on the couplings of anomalous HWW   and HWWγ$HWW\gamma$ vertex, with the design luminosity of 10 fb⁻¹$10{\text{fb}}^{-1}$ and electron beam energy of 140 GeV, through ep→νH+X$ep\to \nu H+X$, γp→WH+X$\gamma p\to WH+X$ and eγ→WHν$e\gamma \to WH\nu$ processes by considering the new physics energy scale to be Λ=1 TeV$\Lambda =1\text{TeV}$. The sensitivity of the LHeC to the new physics scale is also briefly discussed.     

All possible lightest supersymmetric particles in R-parity violating minimal supergravity models

We investigate, which lightest supersymmetric particles can be obtained via a non-vanishing lepton- or baryon-number violating operator at the grand unification scale within the R-parity violating minimal supergravity model. We employ the full one-loop renormalization group equations. We take into account restrictions from the anomalous magnetic moment of the muon and b→sγ$b\to s\gamma$, as well as collider constraints from LEP and the Tevatron. We also consider simple deformations of minimal supergravity models.     

Normalizing inclusive rare B decays

The inclusive semileptonic branching ratio is often employed to normalize other inclusive B   decays. Using recent determinations of the non-perturbative parameters of the Operator Product Expansion we compute the normalization factor for the branching ratio of B→Xsγ$B\to X_s\gamma$ and find a few percent enhancement with respect to previous determinations.     

Probing photon helicity in radiative B decays via charmonium resonance interference

We investigate a new method to probe the helicity of the photon emitted in the b→sγ$b\to s\gamma$ transition. The method relies on the observation of interference effects between two resonance contributions, B→K^∗(Kγ)γ$B\to K^{\ast }(K\gamma )\gamma$ and B→ηc(γγ)K$B\to {\eta }_c(\gamma \gamma )K$ or B→χ_c0(γγ)K$B\to {\chi }_{c0}(\gamma \gamma )K$ to the same final state Kγγ  . Decays of the type B→Kres(Kγ)γ$B\to K_{\mathrm{res}}(K\gamma )\gamma$ dominate the B→Kγγ$B\to K\gamma \gamma$ yield throughout most of the phase space, and may be accessible at current B meson facilities already.     

SUSY GUTs with Yukawa unification: A go/no-go study using FCNC processes

We address the viability of exact Yukawa unification in the context of general SUSY GUTs with universal soft-breaking sfermion and gaugino mass terms at the GUT scale. We find that this possibility is challenged, unless the squark spectrum is pushed well above the limits allowed by naturalness. This conclusion is assessed through a global fit using electroweak observables and quark flavour-changing neutral current (FCNC) processes. The problem is mostly the impossibility of accommodating simultaneously the bottom mass and the BR(B→Xsγ)$\mathrm{BR}(B\to X_s\gamma )$, after the stringent CDF upper bound on the decay Bs→μ⁺μ⁻$B_s\to {\mu }^{+}{\mu }^{-}$ is taken into account, and under the basic assumption that the b→sγ$b\to s\gamma$ amplitude have like sign with respect to the Standard Model one, as indicated by the B→Xs?⁺?⁻$B\to X_s{?}^{+}{?}^{-}$ data.     

The apparent excess in the Higgs to di-photon rate at the LHC: New Physics or QCD uncertainties?

The Higgs boson with a mass _MH≈126 GeV$M_H\approx 126\text{GeV}$ has been observed by the ATLAS and CMS experiments at the LHC and a total significance of about five standard deviations has been reported by both collaborations when the channels H→γγ$H\to \gamma \gamma$ and H→ZZ→4?$H\to ZZ\to 4?$ are combined. Nevertheless, while the rates in the later search channel appear to be in accord with those predicted in the Standard Model, there seems to be an excess of data in the case of the H→γγ$H\to \gamma \gamma$ discovery channel. Before invoking new physics contributions to explain this excess in the di-photon Higgs rate, one should verify that standard QCD effects cannot account for it. We describe how the theoretical uncertainties in the Higgs boson cross section for the main production process at the LHC, gg→H$gg\to H$, which are known to be large, should be incorporated in practice. We further show that the discrepancy between the theoretical prediction and the measured value of the gg→H→γγ$gg\to H\to \gamma \gamma$ rate, reduces to about one standard deviation when the QCD uncertainties are taken into account.     

Pion radiative weak decays in nonlocal chiral quark models

We analyze the radiative pion decay π⁺→e⁺νeγ${\pi }^{+}\to e^{+}{\nu }_e\gamma$ within nonlocal chiral quark models that include wave function renormalization. In this framework we calculate the vector and axial-vector form factors FV$F_V$ and FA$F_A$ at q²=0$q^2=0$ — where q²$q^2$ is the e⁺νe$e^{+}{\nu }_e$ squared invariant mass — and the slope a   of FV(q²)$F_V(q^2)$ at q²→0$q^2\to 0$. The calculations are carried out considering different nonlocal form factors, in particular those taken from lattice QCD evaluations, showing a reasonable agreement with the corresponding experimental data. The comparison of our results with those obtained in the (local) NJL model and the relation of FV$F_V$ and a   with the form factor in π⁰→γ^?γ${\pi }^0\to {\gamma }^{?}\gamma$ decays are discussed.     

Higgs-boson couplings beyond the Standard Model

The implications for Higgs decays of potential new physics beyond the Standard Model (BSM) are considered in the context of effective field theory, assuming perturbative decoupling. Using existing data to restrict which dimension-six operators can arise, it is shown that, given the existing experimental constraints, only a small number of operators can affect the decays of the Higgs: those that may be potentially-tree-generated (PTG) and modify the Higgs–fermion couplings, or those that may be loop-generated (LG) that modify the Higgs couplings to γγ, Zγ and GG  . Implications for specific branching ratios are given in terms of the coefficients of various dimension-six operators. In such a scenario, the ratios Γ(H→WW^?)/Γ(H→ZZ^?)$\Gamma (H\to W{W}^{?})/\Gamma (H\to Z{Z}^{?})$ and Γ(H→W?ν)/Γ(H→Z??)$\Gamma (H\to W?\nu )/\Gamma (H\to Z??)$ equal to their Standard Model values to an accuracy of O(1%)$O(1\text{\%})$ or less.     

Electric dipole moments in pseudo-Dirac gauginos

The SUSY CP problem is one of serious problems in construction of realistic supersymmetric standard models. We consider the problem in a framework in which adjoint chiral multiplets are introduced and gauginos have Dirac mass terms induced by a U(1)$\mathrm{U}(1)$ gauge interaction in the hidden sector. This is realized in hidden sector models without singlet chiral multiplets, which are favored from a recent study of the Polonyi problem. We find that the dominant contributions to electron and neutron electric dipole moments (EDMs) in the model come from phases in the supersymmetric adjoint mass terms. When the supersymmetric adjoint masses are suppressed by a factor of ∼100 compared with the Dirac ones, the electron and neutron EDMs are suppressed below the experimental bound even if the SUSY particle masses are around 1 TeV. Thus, this model works as a framework to solve the SUSY CP problem.     

Search for lepton flavor violation in supersymmetric models via meson decays

Considering the constraints from the experimental data on μ→eγ$\mu \to e\gamma$, μ→3e$\mu \to 3e$, μ–e$\mu \text{–}e$ conversion, etc., we analyze the lepton flavor violating decays ?(J/Ψ,?(1S))→e⁺μ⁻(μ⁺τ⁻)$?(J/\Psi ,?(1S))\to e^{+}{\mu }^{-}({\mu }^{+}{\tau }^{-})$ in the scenarios of the minimal supersymmetric extensions of Standard Model with seesaw mechanism. Numerically, there is parameter space that the LFV processes of J/Ψ(?)→μ⁺τ⁻$J/\Psi (?)\to {\mu }^{+}{\tau }^{-}$ can reach the upper experimental bounds, meanwhile the theoretical predictions on μ→eγ$\mu \to e\gamma$, μ→3e$\mu \to 3e$, μ–e$\mu \text{–}e$ conversion satisfy the present experimental bounds. For searching of new physics, lepton flavor violating processes J/Ψ(?)→μ⁺τ⁻$J/\Psi (?)\to {\mu }^{+}{\tau }^{-}$ may be more promising and effective channels.     

Model-independent measurement of the top quark polarisation

We introduce a new asymmetry in the decay t→Wb→?νb$t\to Wb\to ?\nu b$, which is shown to be directly proportional to the polarisation of the top quark along a chosen axis, times a sum of W helicity fractions. The latter have already been precisely measured at the Tevatron and the Large Hadron Collider. Therefore, this new asymmetry can be used to obtain a model-independent measurement of the polarisation of top quarks produced in any process at hadron or lepton colliders.     

Suppression of flavor symmetry breaking in B decay sum rules

While flavor symmetries are useful for studying hadronic B   decays, symmetry relations for amplitudes and decay rates are usually violated by first order symmetry breaking corrections. We point out two cases in which first order symmetry breaking is suppressed by a small ratio of amplitudes: (1) An isospin sum rule for four B→Kπ$B\to K\pi$ decays, where isospin breaking is shown to be negligible. (2) An SU(3)$\mathrm{SU}(3)$ sum rule for pairs of B→Kπ$B\to K\pi$ and B→Kη₈$B\to K{\eta }_8$, generalized to pairs of B→Kπ$B\to K\pi$, B→Kη$B\to K\eta$ and B→Kη^′$B\to K{\eta }^{\prime }$.     

Leading logarithms in the anomalous sector of two-flavour QCD

We add the Wess–Zumino–Witten term to the N=3$N=3$ massive nonlinear sigma model and study the leading logarithms in the anomalous sector. We obtain the leading logarithms to six loops for π⁰→γ^?γ^?${\pi }^0\to {\gamma }^{?}{\gamma }^{?}$ and to five loops for γ^?πππ${\gamma }^{?}\pi \pi \pi$. In addition we extend the earlier work on the mass and decay constant to six loops and the vector form factor to five loops. We present numerical results for the anomalous processes and the vector form factor. In all cases the series are found to converge rapidly.     

Understanding the radiative decays of vector charmonia to light pseudoscalar mesons

We show that the newly measured branching ratios of vector charmonia (J/ψ$J/\psi$, ψ^′${\psi }^{\prime }$ and ψ(3770)$\psi (3770)$) into γP, where P   stands for light pseudoscalar mesons π⁰${\pi }^0$, η  , and η^′${\eta }^{\prime }$, can be well understood in the framework of vector meson dominance (VMD) in association with the ηc–η(η^′)${\eta }_c\text{–}\eta ({\eta }^{\prime })$ mixings due to the axial gluonic anomaly. These two mechanisms behave differently in J/ψ$J/\psi$ and ψ^′→γP${\psi }^{\prime }\to \gamma P$. A coherent understanding of the branching ratio patterns observed in J/ψ(ψ^′)→γP$J/\psi ({\psi }^{\prime })\to \gamma P$ can be achieved by self-consistently including those transition mechanisms at hadronic level. The branching ratios for ψ(3770)→γP$\psi (3770)\to \gamma P$ are predicted to be rather small.