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.     

Higgs boson search significance deformations due to mixed-in scalars

The existence of exotic scalars that mix with the Standard Model (SM) Higgs boson can affect Higgs boson phenomenology in a multitude of ways. We consider two light Higgs bosons with shared couplings to SM fields and with masses close to each other, in the range where the h→WW→lνlν$h\to WW\to l\nu l\nu$ is an important search channel. In this channel, we do not find the dilution of significance of the ‘SM-like’ Higgs boson that is naively expected because of the mixing. This is because of leakage of events from the other scalar into its signal region. Nevertheless, we show that the broadening of the h→WW→lνlν$h\to WW\to l\nu l\nu$ significance plots of Standard Model Higgs boson searches could indicate the first evidence of the extra scalar state.     

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.     

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.     

B-decay signatures of warped top-condensation

We point out that the light radion ?   in a recently proposed Warped Top-Condensation Model (WTCM), can provide distinct signatures in b→s?$b\to s?$, where the on-shell ? can decay with displaced vertices. We find that some of the parameter space of these models is constrained by B-meson and astrophysical data. Future B-decay measurements can lead to the discovery of the WTCM.     

Top quark forward–backward asymmetry

The recent forward–backward asymmetry recorded by the CDF Collaboration for the top and anti-top quark pair production indicates more than 2σ   deviation from the Standard Model prediction, while its total production cross section remains consistent. We propose a W^′$W^{\prime }$ boson that couples to down and top quarks. We identify the parameter space that can give rise a large enough forward–backward asymmetry without producing too many top and anti-top quark pairs. Other models presented previously in the literature that can produce such effects are also briefly discussed.     

Detecting Higgs bosons with muons at hadron colliders

We investigate the prospects for the discovery of neutral Higgs bosons with a pair of muons by direct searches at the CERN large hadron collider (LHC) as well as by indirect searches in the rare decay Bs→μ⁺μ⁻$B_s\to {\mu }^{+}{\mu }^{-}$ at the Fermilab Tevatron and the LHC. Promising results are found for the minimal supersymmetric standard model, the minimal supergravity (mSUGRA) model, and supergravity models with non-universal Higgs masses (NUHM SUGRA). For tanβ?50$\tan \beta ?50$, we find that (i) the contours for a branching fraction of B(Bs→μ⁺μ⁻)=1×¹⁰⁻⁸$B(B_s\to {\mu }^{+}{\mu }^{-})=1\times {10}^{\mathrm{-8}}$ in the parameter space are very close to the 5σ   contours for pp→b?⁰→bμ⁺μ⁻+X$pp\to b{?}^0\to b{\mu }^{+}{\mu }^{-}+X$, ?⁰=h⁰${?}^0=h^0$, H⁰$H^0$, A⁰$A^0$ at the LHC with an integrated luminosity (L) of 30 fb⁻¹, (ii) the regions covered by B(Bs→μ⁺μ⁻)?5×¹⁰⁻⁹$B(B_s\to {\mu }^{+}{\mu }^{-})?5\times {10}^{\mathrm{-9}}$ and the discovery region for b?⁰→bμ⁺μ⁻$b{?}^0\to b{\mu }^{+}{\mu }^{-}$ with 300 fb⁻¹ are complementary in the mSUGRA parameter space, (iii) in NUHM SUGRA models, a discovery of B(Bs→μ⁺μ⁻)?5×¹⁰⁻⁹$B(B_s\to {\mu }^{+}{\mu }^{-})?5\times {10}^{\mathrm{-9}}$ at the LHC will cover regions of the parameter space beyond the direct search for b?⁰→bμ⁺μ⁻$b{?}^0\to b{\mu }^{+}{\mu }^{-}$ with L=300 fb⁻¹$L=300{\text{fb}}^{\mathrm{-1}}$.     

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.     

Constraints on unparticle physics in electroweak gauge boson scattering

The existence of scale invariant physics would lead to new phenomena in particle physics that could be detected at the LHC. In this Letter we exploit the effects of these unparticles in WW→WW$WW\to WW$ scattering. From the requirement of unitarity we derive constraints on unparticle physics. We show that the existence of unparticles would lead to deviations in differential cross sections which can be measured. These deviations are sensitive on the scale dimension and on the spin characteristics of the unparticles.     

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.