arXiv subjects

A. G. Akeroyd

Publications and source records attributed to A. G. Akeroyd.

At least 37 records · Page 2Linked to original sources

arXiv2012

The decay Bs -> mu+ mu-: updated SUSY constraints and prospects

We perform a study of the impact of the recently released limits on BR(Bs -> mu+ mu-) by LHCb and CMS on several SUSY models. We show that the obtained constraints can be superior to those which are derived from direct searches for SUSY particles in some scenarios, and the use of a double ratio of purely leptonic decays involving Bs -> mu+ mu- can further strengthen such constraints. We also discuss the experimental sensitivity and prospects for observation of Bs -> mu+ mu- during the sqrt(s)=7 TeV run of the LHC, and its potential implications.

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arXiv2011

Production of doubly charged scalars from the decay of singly charged scalars in the Higgs Triplet Model

The existence of doubly charged Higgs bosons (H^{\pm\pm}) is a distinctive feature of the Higgs Triplet Model (HTM), in which neutrinos obtain tree-level masses from the vacuum expectation value of a neutral scalar in a triplet representation of SU(2)_L. We point out that a large branching ratio for the decay of a singly charged Higgs boson to a doubly charged Higgs boson via H^\pm\to H^{\pm\pm}W^* is possible in a sizeable parameter space of the HTM. From the production mechanism q'qbar\to W^* \to H^{\pm\pm}H^\mp the above decay mode would give rise to pair production of H^{\pm\pm}, with a cross section which can be comparable to that of the standard pair-production mechanism qqbar\to γ^*,Z^* \to H^{++}H^{--}. We suggest that the presence of a sizeable branching ratio for H^\pm\to H^{\pm\pm}W^* could significantly enhance the detection prospects of H^{\pm\pm} in the four-lepton channel. Moreover, the decays H^0\to H^\pm W^* and A^0\to H^\pm W^* from production of the neutral triplet scalars H^0 and A^0 would also provide an additional source of H^\pm, which can subsequently decay to H^{\pm\pm}.

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arXiv2011

Production of doubly charged scalars from the decay of a heavy SM-like Higgs boson in the Higgs Triplet Model

The Higgs Triplet Model (HTM) of neutrino mass generation predicts the existence of doubly charged Higgs bosons (H^{\pm\pm}). In the HTM a scalar eigenstate (H_2) is dominantly composed of the scalar field from the isospin doublet, and could be significantly heavier than H^{\pm\pm}. Such a scenario would allow the possibility of a large branching ratio for the decay H_2-> H^{++}H^{--}. From the production mechanism of gluon-gluon fusion, gg-> H_2, the above decay mode would give rise to pair production of doubly charged Higgs bosons (H^{++}H^{--}) with a cross section which could be significantly larger than the cross sections for the standard production mechanisms qqbar -> γ,Z-> H^{++}H^{--} and q'qbar -> W -> H^{\pm\pm}H^{\mp}. We discuss the phenomenological consequences for the ongoing searches for H^{\pm\pm} at the Tevatron and at the LHC.

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arXiv2010

Leptonic signatures of doubly charged Higgs boson production at the LHC

The production of doubly charged Higgs bosons (H^{\pm\pm}) at the CERN LHC can give rise to distinctive multi-lepton signatures. The discovery potential of H^{\pm\pm} can be optimized by considering a search strategy which is sensitive to both of the dominant production mechanisms, q\bar q\to H^{++}H^{--} and q\bar {q'}\to H^{\pm\pm}H^{\mp}. We compare the discovery potential for the signatures of exactly four leptons and at least three leptons in the final state, using the same set of cuts. We have carried out fast detector simulations at the LHC for both signal and backgrounds for a wide range of values of the charged Higgs mass. We find that the use of the latter channel can substantially improve the detection prospects of the doubly charged Higgs boson at the LHC.

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arXiv2010

Fermiophobia in a Higgs Triplet Model

A Fermiophobic Higgs boson can arise in models with an extended Higgs sector, such as models with scalars in an isospin triplet representation. In a specific model with a scalar triplet and spontaneous violation of lepton number induced by a scalar singlet field, we show that fermiophobia is not a fine-tuned situation, unlike in Two Higgs Doublet Models. We study distinctive signals of fermiophobia which can be probed at the LHC. For the case of a small Higgs mass a characteristic signal would be a moderate B(H ->γγ) accompanied by a large B(H -> JJ) (where J is a Majoron), the latter being an invisible decay. For the case of a large Higgs mass there is the possibility of dominant H -> ZZ, WW and suppressed H -> JJ decay modes. In this situation, B(H -> ZZ) is larger than B(H -> WW), which differs from the SM prediction.

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arXiv2010

Measuring V_ub and probing SUSY with double ratios of purely leptonic decays of B and D mesons

The experimental prospects for precise measurements of the leptonic decays B_u -> tau nu / mu nu, B_s -> mu+ mu-, D -> mu nu and D_s -> mu nu / tau nu are very promising. Double ratios involving four of these decays can be defined in which the dependence on the values of the decay constants is essentially eliminated, thus enabling complementary measurements of the CKM matrix element V_ub with a small theoretical error. We quantify the experimental error in a possible future measurement of |V_ub| using this approach, and show that it is competitive with the anticipated precision from the conventional approaches. Moreover, it is shown that such double ratios can be more effective than the individual leptonic decays as a probe of the parameter space of supersymmetric models. We emphasize that the double ratios have the advantage of using |V_ub| as an input parameter (for which there is experimental information), while the individual decays have an uncertainty from the decay constants (e.g. f_B_s), and hence a reliance on theoretical techniques such as lattice QCD.

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arXiv2010

Phenomenology of Large Mixing for the CP-even Neutral Scalars of the Higgs Triplet Model

The Higgs Triplet Model contains two CP-even neutral scalar eigenstates, each having components from an isospin doublet and an isospin triplet scalar field. The mixing angle can be maximal if the masses of the scalar eigenstates are close to degeneracy. We quantify the dependence of the mixing angle on the mass splitting and on the vacuum expectation value of the neutral triplet scalar. We determine the parameter space for maximal mixing, and study the observability of both CP-even Higgs bosons at the CERN LHC

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arXiv2009

Doubly charged Higgs bosons and three-lepton signatures in the Higgs Triplet Model

Doubly charged Higgs bosons, H^{\pm\pm}, are being searched for in the Tevatron experiments. The most recent search by the D0 collaboration seeks three muons (mu^\pmμ^\pmμ^\mp), which are assumed to originate from the pair-production process, q\overline q\to H^{++}H^{--}, followed by the decay H^{\pm\pm} \to μ^\pm μ^\pm. In this three-lepton (3l) channel there are six distinct signatures for l=e or μ. In the context of the Higgs Triplet Model, we quantify the dependence of the event numbers for the 3l channels on the parameters of the neutrino mass matrix. It is also shown that the inclusion of the production mechanism q \overline{q'} \to H^{\pm\pm}H^{\mp}, followed by the decay H^\pm\to l^ \pmν, would significantly increase the discovery potential in these channels. We then provide perspectives on the production of these channels at the Tevatron and LHC.

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arXiv2009

Lepton Flavour Violating Decays tau to lll and mu to e gamma in the Higgs Triplet Model

Singly and doubly charged Higgs bosons in the Higgs Triplet Model mediate the lepton flavour violating (LFV) decays tau to \bar{l}ll and mu to e gamma. The LFV decay rates are proportional to products of two triplet Yukawa couplings (h_{ij}) which can be expressed in terms of the parameters of the neutrino mass matrix and an unknown triplet vacuum expectation value. We determine the parameter space of the neutrino mass matrix in which a signal for tau to \bar{l}ll and/or mu to e gamma is possible at ongoing and planned experiments. The conditions for respecting the stringent upper limit for mu to eee are studied in detail, with emphasis given to the possibility of |h_{ee}|\simeq 0 which can only be realized if Majorana phases are present.

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arXiv2009

Constraints on charged Higgs bosons from D(s)+- -> mu+- nu and D(s)+- -> tau+- nu

The decays D(s)+- -> mu+- nu and D(s)+- -> tau+- nu have traditionally been used to measure the D(s)+- meson decay constant f_D(s). Recent measurements at CLEO-c and the B factories suggest a branching ratio for both decays somewhat higher than the Standard Model prediction using f_D(s) from unquenched lattice calculations. The charged Higgs boson (H+-) in the Two Higgs Doublet Model (Type II) would also mediate these decays, but any sizeable contribution from H+- can only suppress the branching ratios and consequently is now slightly disfavoured. It is shown that constraints on the parameters tan(beta) and m_H+- from such decays can be competitive with and complementary to analogous constraints derived from the leptonic meson decays B+- -> tau+- nu_tau and K+- -> mu+- nu_mu, especially if lattice calculations eventually prefer f_D(s) < 250 MeV.

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arXiv2008

Charged Higgs in the NMSSM

The charged Higgs boson decays $H^\pm\to W^\pm A_1$ and $H^\pm\to W^\pm h_i$ are studied in the framework of the next-to Minimal Supersymmetric Standard Model (NMSSM). It is found that the decay rate for H^\pm\to W^\pm A_1 can dominate both below and above the top-bottom threshold. We suggest that p p\to H^\pm A_1 is a promising discovery channel for a light charged Higgs boson in the NMSSM with small or moderate \tanβand dominant decay mode H^\pm \to W^\pm A_1 which leads to W^\pm A_1 A_1. This W^\pm A_1 A_1 signature can also arise from the Higgsstrahlung process pp\to W^\pm h_1 followed by the decay h_1\to A_1 A_1. It is shown that there exist regions of parameter space where these processes can have comparable cross sections and we suggest that their respective signals can be distinguished at the LHC by using appropriate reconstruction methods.

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arXiv2008

Measuring B -> tau nu and B_c -> tau nu at the Z peak

The measurement of B->tau nu at the B factories provides important constraints on the parameter tan beta/m_H^+- in the context of models with two Higgs doublets. Limits on this decay from e+e- collisions at the Z peak were sensitive to the sum of B->tau nu and B_c->tau nu. Due to the possibly sizeable contribution from B_c->tau nu we suggest that a signal for this combination might be observed if the LEP L3 Collaboration used their total data of ~3.6 10^6 hadronic decays of the Z boson. Moreover, we point out that a future Linear Collider operating at the Z peak (Giga Z option) could constrain tan beta/m_H^+- from the sum of these processes with a precision comparable to that anticipated at proposed high luminosity B factories from B-> tau nu alone.

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arXiv2008

Probing Majorana Phases and Neutrino Mass Spectrum in the Higgs Triplet Model at the LHC

Doubly charged Higgs bosons (H^++) are a distinctive signature of the Higgs Triplet Model of neutrino mass generation. If H^++ is relatively light (m_{H^++} < 400GeV) it will be produced copiously at the LHC, which could enable precise measurements of the branching ratios of the decay channels H^++ to l_i l_j. Such branching ratios are determined solely by the neutrino mass matrix which allows the model to be tested at the LHC. We quantify the dependence of the leptonic branching ratios on the absolute neutrino mass and Majorana phases, and present the permitted values for the channels ee, emu and mumu. It is shown that precise measurements of these three branching ratios are sufficient to extract information on the neutrino mass spectrum and probe the presence of CP violation from Majorana phases.

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arXiv2008

Charged Higgs bosons in the Next-to MSSM (NMSSM)

The charged Higgs boson decays $H^\pm\to W^\pm A_1$ and $H^\pm\to W^\pm h_i$ are studied in the framework of the next-to Minimal Supersymmetric Standard Model (NMSSM). It is found that the decay rate for $H^\pm\to W^\pm A_1$ can exceed the rates for the $τ^\pmν$ and $tb$ channels both below and above the top-bottom threshold. The dominance of $H^\pm\to W^\pm A_1$ is most readily achieved when $A_1$ has a large doublet component and small mass. We also study the production process $pp\to H^\pm A_1$ at the LHC followed by the decay $H^\pm\to W^\pm A_1$ which leads to the signature $W^\pm A_1 A_1$. We suggest that $p p\to H^\pm A_1$ is a promising discovery channel for a light charged Higgs boson in the NMSSM with small or moderate $\tanβ$ and dominant decay mode $H^\pm \to W^\pm A_1$. This $W^\pm A_1 A_1$ signature can also arise from the Higgsstrahlung process $pp\to W^\pm h_1$ followed by the decay $h_1\to A_1 A_1$. It is shown that there exist regions of parameter space where these processes can have comparable cross sections and we suggest that their respective signals can be distinguished at the LHC by using appropriate reconstruction methods.

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arXiv2007

Effect of Charged Scalar Loops on Photonic Decays of a Fermiophobic Higgs

Higgs bosons with very suppressed couplings to fermions ("Fermiophobic Higgs bosons", h_f) can decay to two photons (γγ) with a branching ratio significantly larger than that expected for the Standard Model Higgs boson for m_{h_f}<150 GeV. Such a particle would give a clear signal at the LHC and can arise in the Two Higgs Doublet Model (type I) in which h_f -> γγis mediated by W^+ and charged Higgs boson (H^+) loops. We show that the H^+ loops can cause both constructive and destructive contributions with a magnitude considerably larger than the anticipated precision in the measurement of the photonic decay channel at future hadron and lepton colliders.

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arXiv2007

Lepton Flavour Violating tau Decays in the Left-Right Symmetric Model

The Left-Right symmetric extension of the Standard Model with Higgs isospin triplets can provide neutrino masses via a TeV scale seesaw mechanism. The doubly charged Higgs bosons H^{\pm\pm}_L and H^{\pm\pm}_R induce lepton flavour violating decays τ^\pm \to lll at tree-level via a coupling which is related to the Maki-Nakagawa-Sakata matrix (V_{\rm MNS}). We study the magnitude and correlation of τ^\pm \to lll and μ\to eγwith specific assumptions for the origin of the large mixing in V_{\rm MNS} while respecting the stringent bound for μ\to eee. It is also shown that an angular asymmetry for τ^\pm \to lll is sensitive to the relative strength of the H^{\pm\pm}_L and H^{\pm\pm}_R mediated contributions and provides a means of distinguishing models with doubly charged Higgs bosons.

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arXiv2007

Effect of H^\pm on B^\pm\to τ^\pmν_τand D^\pm_s\to μ^\pmν_μ,τ^\pmν_τ

The recent observation of the purely leptonic decay B^\pm\to τ^\pmν_τat the B factories permits a sizeable contribution from a charged Higgs boson (H^\pm). Such a H^\pm would also contribute to the decays D^\pm_s\to μ^\pmν_μand D^\pm_s\to τ^\pmν_τ, which are being measured with increasing precision at CLEO-c. We show that the branching ratios of D^\pm_s\to μ^\pmν_μand D^\pm_s\to τ^\pmν_τcould be suppressed by up to 10% from the Standard Model prediction, which is larger than the anticipated precision in the measurements of these decays at forthcoming BES-III.

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arXiv2007

$B\to η^{(\prime)} (\ell^{-} \barν_{\ell}, \ell^{+} \ell^{-}, K, K^*)$ decays in the quark-flavor mixing scheme

In the quark-flavor mixing scheme, $η$ and $η'$ are linear combinations of flavor states $η_{q}=(u\bar{u}+d\bar{d})/\sqrt{2}$ and $η_{s}=s\bar{s}$ with the masses of $m_{qq}$ and $m_{ss}$, respectively. Phenomenologically, $m_{ss}$ is strictly fixed to be around 0.69, which is close to $\sqrt{2m^{2}_{K}-m^{2}_π}$ by the approximate flavor symmetry, while $m_{qq}$ is found to be $0.18\pm 0.08$ GeV. For a large allowed value of $m_{qq}$, we show that the BRs for $B\to η^{(\prime)} X$ decays with $X=(\ell^{-} \barν_{\ell}, \ell^{+} \ell^{-})$ are enhanced. We also illustrate that $BR(B\toηX)> BR(B\to η^{\prime} X)$ in the mechanism without the flavor-singlet contribution. Moreover, we demonstrate that the decay branching ratios (BRs) for $B\to η^{(\prime)}K^{[*]}$ are consistent with the data. In particular, the puzzle of the large $BR(B\to η^{\prime} K)$ can be solved. In addition, we find that the CP asymmetry for $B^{\pm}\to ηK^{\pm}$ can be as large as -30%, which agrees well with the data. However, we cannot accommodate the CP asymmetries of $B\to ηK^*$ in our analysis, which could indicate the existence of some new CP violating sources.

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