Talk given at the SUSY09 conference in Boston, June 2009. 4 pages, 3 figures. To be published in the American Institute of Physics Conference Proceedings
This is a short review of the framework proposed in \cite{Goh:2009wg} which gives rise to indirect Dark Matter (DM) signals explaining the recent cosmic-ray anomalies and links cosmic-ray signals of DM to LHC signals of a leptonic Higgs sector.The states of the leptonic Higgs doublet are lighter than about 200 GeV, yielding large 2 tau and 4 tau event rates at the LHC. For the case of annihilations, cosmic photon and neutrino signals are constrained.
We propose that the leptonic cosmic ray signals seen by PAMELA and ATIC result from the annihilation or decay of dark matter particles via states of a leptonic Higgs doublet to $τ$ leptons, linking cosmic ray signals of dark matter to LHC signals of the Higgs sector. The states of the leptonic Higgs doublet are lighter than about 200 GeV, yielding large $\barτ τ$ and $\barτ τ\barτ τ$ event rates at the LHC. Simple models are given for the dark matter particle and its interactions with the leptonic Higgs, for cosmic ray signals arising from both annihilations and decays in the galactic halo. Fo…
We summarized our report on leptonic flavor violating Higgs decay into mu + tau under the scheme of a generic supersymmetric standard model without R parity. With known experimental constraints imposed, important combinations of R-parity violating parameters which can give notable branching ratios are listed.
Leptonic decays of vector-states of bottomonium are analized searching for a light pseudoscalar Higgs-like neutral boson manifesting via an apparent breaking of lepton universality.
A leptonic $(\bar l l)$ decay of a heavy quark-antiquark bound state $T(\bar QQ)$ with a Higgs-boson $H$ emission is investigated. The applying of the well-known low-energy theorem to meson-Higgs coupling allows one to estimate the probability of the decay $T(\bar QQ)\to \bar ll H$. The only a simple version of the Standard Model extension containing two-Higgs doublet is considered.
We construct extensions of the Standard Model with two Higgs doublets, where there are flavour changing neutral currents both in the quark and leptonic sectors, with their strength fixed by the fermion mixing matrices $V_{CKM}$ and $V_{PMNS}$. These models are an extension to the leptonic sector of the class of models previously considered by Branco, Grimus and Lavoura, for the quark sector. We consider both the cases of Dirac and Majorana neutrinos and identify the minimal discrete symmetry required in order to implement the models in a natural way.
The radiative leptonic $B_{c}\toτ\bar{ν_τ}γ$ decay is analysed in context of 2HDM. It is shown that with large values of $tanβ$, the contributions of Model II to the decay rate exceeds considerably the Standard Model ones, while the contributions of Model I overlap with the Standard Model predictions.
The implementation of maximally restrictive texture zeros in the leptonic sector is investigated in the context of two-Higgs-doublet models with Majorana neutrinos. After analyzing all maximally restrictive pairs of leptonic mass matrices with zero entries, we conclude that there are only four texture combinations that are compatible with observations at 3 sigma confidence level and can be implemented through Abelian symmetries in a two-Higgs-doublet model. The compatibility of these textures with current constraints on lepton-flavor-violating processes is also studied. The ultraviolet complet…
The littlest $Higgs$ model with T-parity (called the $LHT$ model) predicts the existence of the T-odd leptons, which can generate contributions to some leptonic processes at the one-loop level. We calculate their contributions to the leptonic $Z$ decay processes $Z\to l\bar{l'}$, $Z\to l\bar{l}$, and $Z\rightarro ν\barν$. We find that the T-odd leptons can give significant contributions to the branching ratios of these decay processes in most of the parameter space. The experimental measurement values might generate constraints on the free parameters of the $LHT$ model.
We consider the version of the Zee model where both Higgs doublets couple to leptons. Within this framework we study charged Higgs decays. We focus on a model with minimal number of parameters consistent with experimental neutrino data. Using constraints from neutrino physics we (i) discuss the reconstruction of the parameter space of the model using the leptonic decay patterns of both of the two charged Higgses, $h_{1,2}^{+}\to \ell_{j}^{+}ν_{i}$, and the decay of the heavier charged Higgs, $h_{2}^{+}\to h^{+}_{1}h^{0}$; (ii) show that the decay rate $Γ(h_{1}^{+}\to μ^{+}ν_{i})$ in general is…
In this work, we study the radiative leptonic decays of $B^-$ and $D^-$ mesons in the standard model and the two-Higgs-doublet-model type II. The results are obtained using the factorization procedure, and the contribution of the order $O(Λ_{\rm QCD}\left/m_Q\right.)$ is included. The numerical results are calculated using the wave-function obtained in relativistic potential model. As a result, the decay mode $B\to γτν_τ$ is found to be sensitive to the effect of the charged Higgs boson. Using the constraint on the free parameters of the two Higgs doublet model given in previous works, we find…
We address the observed discrepancies in the anomalous magnetic dipole moments (MDM) of the muon and electron by extending the inert two Higgs Doublet Model (2HDM) with SM gauge singlet complex scalar field and singlet Vector-like Lepton (VLL) field. We obtain the allowed parameter space constrained from the Higgs decays to gauge Bosons at LHC, LEP II data and electro-weak precision measurements. The muon and electron MDM's are then explained within a common parameter space for different sets of allowed couplings and masses of the model particles.
The type X (lepton-specific) two-Higgs-doublet model at large $\tanβ$ becomes leptophilic and thus allows a light pseudoscalar $A$ accommodating the observed muon $g-2$ deviation without conflicting with various hadronic constraints. On the other hand, it is strongly constrained by leptonic precision observables such as lepton universality test in the neutral and charged currents. Treating all the lepton universality data in a consistent way, we show how the current data constrain the parameter space of $m_A$ and $\tanβ$ for given degenerate masses of heavy Higgs bosons $H$ and $H^\pm$. While …
We consider the effect of complex Higgs triplets on purely leptonic processes and survey the experimental constraints on the mass and couplings of their single and double charge members. Present day experiments tolerate values of the Yukawa couplings of these scalars at the level of the standard electroweak gauge couplings. We show that the proposed measurement of the ratio $R_{LCD}=σ(ν_μe)/ [σ(\bbν_μe) + σ(ν_e e )]$ would allow to explore a large region of the parameter space inaccessible to the usual ratio $R=σ(ν_μe)/σ(\bbν_μe)$.
Higgs boson mass measurement at $\sim 125$ GeV points to a high scale for SUSY specifically the scalar masses. If all the scalars are heavy, supersymmetric contribution to the leptonic $g-2$ moments will be significantly reduced. On the other hand the Brookhaven experiment indicates a 3sigma deviation from the standard model prediction. Here we analyze the leptonic $g-2$ moments in an extended MSSM model with inclusion of a vector like leptonic generation which brings in new sources of CP violation. In this work we consider the contributions to the leptonic $g-2$ moments arising from the excha…
We reanalyze the extraction of the heavy Higgs boson signal $H\rightarrow W^+W^-\rightarrow \bar\ellν,\ell\barν$ $(\ell=e\hbox{ or }μ)$ from the Standard Model background at hadron supercolliders, taking into account revised estimates of the top quark background. With new acceptance criteria the detection of the signal remains viable. Requiring a forward jet-tag, a central jet-veto, and a large relative transverse momentum of the two charged leptons yields $S/\sqrt B>6$ for one year of running at the SSC or LHC.
Large long-distance standard model effects in FCNC semileptonic D decays can make observable these processes in future measurements. Eventual disagreements in this sector and/or the observation of lepton family violating (LFV) D decays would require an explanatio beyond the SM framework. In this paper we confront present experimental data on leptonic and semileptonic FCNC and LFV D meson decays with a version of the two-Higgs doublet model that allows these effects to occur at tree- level. The stringent bounds on the parameters of the model are obtained from D^0 --> l^+l'^- and D --> pi l^+l'^…
We derive the leptonic neutral current in the simplest little Higgs model and compute the contribution of the model to the decay width $Z \to e^+e^-$. Using the precision electroweak data we obtain a strong lower bound $f\geq 5.6$ TeV at 95% C.L. on the characteristic energy scale of the model. It results in a lower bound for the new gauge bosons $W^{\prime\pm}$ and $Z^{\prime}$ as being $M_{W^{\prime\pm}}\geq 2.6$ TeV and $M_{Z^{\prime}}\geq 3.1$ TeV, respectively. We also present the allowed values of the $k=f_1/f_2$ which is the parameter relating the two vacuum expectation values of the sc…
We consider the two-loop corrections to the $HW^+W^-$ vertex at order $αα_s$. We construct a canonical basis for the two-loop integrals using the Baikov representation and the intersection theory. By solving the $ε$-form differential equations, we obtain fully analytic expressions for the master integrals in terms of multiple polylogarithms, which allow fast and accurate numeric evaluation for arbitrary configurations of external momenta. We apply our analytic results to the decay process $H \to ν_e e W$, and study both the integrated and differential decay rates. Our results can also be appli…
CMS has reported indications (2.4σ) of the decay of the Higgs boson into μτ. The simplest explanation for such a decay would be a general Two Higgs Doublet Model (2HDM). In this case, one would expect the heavy neutral Higgs bosons, H and A, to also decay in a similar manner. We study two specific models. The first is the type III 2HDM, and the second is a 2HDM, originally proposed by Branco et al., in which all flavor-changing neutral processes are given by the weak mixing matrix. In the latter model, since mixing between the second and third generations in the lepton sector is large, flavor-…
Searches for a heavy Standard Model Higgs boson focus on the 'gold plated mode' where the Higgs decays to two leptonic Z bosons. This channel provides a clean signature, in spite of the small leptonic branching ratios. We show that using fat jets the semi-leptonic ZZ mode significantly increases the number of signal events with a similar statistical significance as the leptonic mode.
The leptonic mixing angle $θ_{13}$ is known to be small. If it is indeed tiny, the simplest explanation is that charged leptons mix only in the $μ-τ$ sector and neutrinos only in the 1-2 sector. We show that this pattern may be explained by the discrete symmetry $Z_2 \times Z_2$ of a complete Lagrangian, which has 2 Higgs doublets and 2 Higgs triplets (or 2 heavy right-handed singlet neutrinos). In the case of Higgs triplets, the Majorana neutrino masses are arbitrary, whereas in the case of heavy singlet neutrinos, an inverted hierarchy is predicted. Lepton-Flavor-Violation effects, present o…
We perform a systematic analysis of models with GeV-scale dark matter coupled to baryons and leptons. Such theories provide a natural framework to explain the matter-antimatter asymmetry of the universe. We find that only a few baryonic dark matter models are free from tree-level proton decay without explicitly imposing baryon number conservation. We enumerate those cases and provide a brief overview of their phenomenology. We then focus on a leptonic dark matter model for a more detailed discussion of the baryon asymmetry generation via leptogenesis, the symmetry restoration in the dark secto…
If tan(beta) is large, down-type quark mass matrices and Yukawa couplings cannot be simultaneously diagonalized, and flavour violating couplings of the neutral Higgs bosons are induced at the 1-loop level. These couplings lead to Higgs-mediated contributions to the decays B_s -> mu+ mu- and B_d -> tau+ tau-, at a level that might be of interest for the current Tevatron run, or possibly, at B-factories. We evaluate the branching ratios for these decays within the framework of minimal gravity-, gauge- and anomaly-mediated SUSY breaking models, and also in SU(5) supergravity models with non-unive…
We study the Higgs boson decay to W+W-, where one boson decays to leptons, and the other decays to c+jet at Tevatron. Given the current charm tagging acceptances, this channel can help improve and confirm the current combined Tevatron exclusion limit on a standard model-like Higgs boson. If charm acceptance can be improved to at least 24%, this channel could provide the second tightest limits on a Higgs boson mass between 140-190 GeV from a single channel measurement.
The notion of U(1) lepton number (which may only be softly broken) is applied to models of dark matter which interacts with leptons. Previous scotogenic models of Majorana or Dirac neutrino mass are shown to be derivable in this framework without additional symmetries. Only complete renormalizable theories are considered. An explicit class of models with $Z_n$ ($n \geq 5$) lepton and dark symmetry for Dirac neutrinos is derived, as well as an example of $Z_3$ dark symmetry.
The well-known leptonic U(1) symmetry of the standard model of quarks and leptons is extended to include a number of new fermions and scalars. The resulting theory has an invisible QCD axion (thereby solving the strong CP problem), a candidate for weak-scale dark matter, as well as radiative neutrino masses. A possible key connection is a color-triplet scalar, which may be produced and detected at the Large Hadron Collider.
A possible extension of the Standard Model to include lepton number as local gauge symmetry is investigated. In such a model, anomalies are canceled by two extra fermions doublet. After leptonic gauge symmetry spontaneously broken, three active neutrinos may acquire non-zero Majorana masses through the modified Type-II seesaw mechanism. Constraints on the model from electro-weak precision measurements are studied. Due to the $Z_2$ discrete flavor symmetry, right-handed Majorana neutrinos can serve as cold dark matter candidate of the Universe. Constraint from dark matter relic abundance is cal…
A simple and elegant mechanism is proposed to resolve the problem of having a light scalar mediator for self-interacting dark matter and the resulting disruption to the cosmic microwave background (CMB) at late times by the former's enhanced Sommerfeld production and decay. The crucial idea is to have Dirac neutrinos with the conservation of U(1) lepton number extended to the dark sector. The simplest scenario consists of scalar or fermion dark matter with unit lepton number accompanied by a light scalar dilepton mediator, which decays to two neutrinos.
We show that direct CP violation in semi-leptonic and leptonic decays can occur in multi-Higgs doublet extensions of the electroweak standard model with flavor changing neutral currents. For pion and lepton decays these $CP$ violating effects cannot be constrained directly by experimental data since up to now the branching ratio of the decays $π^-$ and $μ^-$ have not been measured in laboratory.
Rare leptonic kaon and pion decays $K^+(π^+) \to μ^+\, ν_μ\, e^+ e^-$ can be used to probe a dark photon of mass ${\cal O}(10)$~MeV, with the background coming from the mediation of a virtual photon. This is most relevant for the 16.7-MeV dark photon proposed to explain a 6.8$σ$ anomaly recently observed in $^8$Be transitions by the Atomki Collaboration. We evaluate the reach of future experiments for different scenarios of how the dark photon couples with the standard model particles, and show that a great portion of the preferred 16.7-MeV dark photon parameter space can be decisively probed.…
We compute the hadronic production of top-antitop pairs in association with a Higgs boson at next-to-leading-order QCD, including the decay of the top and antitop quark into bottom quarks and leptons. Our computation is based on full leading and next-to-leading-order matrix elements for $e^+ ν_e μ^-\barν_μb \bar{b} H(j)$ and includes all non-resonant contributions, off-shell effects and interferences. Numerical results for the integrated cross section and several differential distributions are given for the LHC operating at 13 TeV using a fixed and a dynamical factorization and renormalization…
Possibility of observing associated production of charged Higgs and W boson in the framework of MSSM at LHC is studied. Both leptonic and hadronic decays of W boson are studied while the charged Higgs boson is considered to decay to a $τ$ lepton and a neutrino. Therefore two search categories are defined based on the leptonic and hadronic final states, i.e. $\ell τ+E^{miss}_{T}$ and $jj τ+E^{miss}_{T}$ where $\ell=e$ or $μ$ and $j$ is a light jet from $W$ decay. The discovery chance of the two categories is evaluated at an integrated luminosity of 300 \invfb at LHC. It is shown that both lepto…
Recent observatons of high-energy positrons and electrons by the PAMELA and ATIC experiments may be an indication of the annihilation of dark matter into leptons and not quarks. This leptonic connection was foreseen already some years ago in two different models of radiative neutrino mass. We discuss here the generic interactions (nu eta^0 - l eta^+) chi and l^c zeta^- chi^c which allow this to happen, where chi and/or chi^c are fermionic dark-matter candidates. We point out in particular the importance of chi chi to l^+ l^- gamma to both positron and gamma-ray signals within this framework.
Models of fermion and scalar dark matter abound. Here we consider instead vector dark matter, from an SU(2)_N extension of the standard model. It has a number of interesting properties, including a possible implementation of the inverse seesaw mechanism for neutrino mass. The annihilation of dark matter for calculating its relic abundance in this model is not dominated by its cross section to standard-model particles, but rather to other new particles which are in thermal equilibrium with those of the standard model.
The recently reported excess in XENON1T is explained by new leptonic forces, which are free from gauge anomalies. We focus on two scenarios with and without dark matter. In Scenario #1, the gauge boson of gauged lepton number U(1)$_{L_e-L_j}$, $j=μ$ or $τ$ provides non-standard interaction between solar neutrino and electron that enhances the number of electron recoil events in the XENON1T detector. In Scenario #2, the new gauge boson exclusively couples to electron and dark matter, then cosmic-ray electrons can transfer their momenta to dark matter in halo. The boosted dark matter generates t…
We examine lepton flavor violating (LFV) interactions for heavy right-handed neutrinos that exist in most of the standard model extensions that address dark matter (DM) and neutrino mass at the loop level. In order to probe the collider effect of these LFV interactions, we impose the assumption that the model parameters give the right values of the DM relic density and fulfill the constraints from the LFV processes $\ell_α\rightarrow\ell_βγ$ and $\ell_α\rightarrow3\ell_β$. We also investigate the possibility of probing these interactions, and hence the right-handed neutrino, at leptonic collid…
We study di-boson production via both neutral and charged current at the Large Hadron Collider, i.e. subprocesses $q\bar q\to e^+ν_e μ^-\barν_μ$ + ${\rm{c.c.}}$ and $q\bar q'\to l^+ν_l l^{'+}l^{'-}$ + ${\rm{c.c.}}$, respectively, where $q,q'$ are quarks and $l,l'=e,μ$, in all possible combinations, in the context of the 4-Dimensional Composite Higgs Model. These modes enable the production in the intermediate steps of several additional -- with respect to the Standard Model -- neutral and charged gauge bosons belonging to the spectrum of this scenario, all of which in resonant topologies. We n…
The alternative $[SU(3)]^4$ model of leptonic color and dark matter is discussed. It unifies at $M_U \sim 10^{14}$ GeV and has the low-energy subgroup $SU(3)_q \times SU(2)_l \times SU(2)_L \times SU(2)_R \times U(1)_X$ with $(u,h)_R$ instead of $(u,d)_R$ as doublets under $SU(2)_R$. It has the built-in global $U(1)$ dark symmetry which is generalized $B-L$. In analogy to $SU(3)_q$ quark triplets, it has $SU(2)_l$ hemion doublets which have half-integral charges and are confined by $SU(2)_l$ gauge bosons (stickons). In analogy to quarkonia, their vector bound states (hemionia) are uniquely sui…
The Little Higgs model with T-parity (LHT) belongs to the non-minimal flavour violating model. This model has new sources of flavour and CP violation both in quark and leptonic sectors. These new sources of flavour violation originates by the interaction of Standard Model (SM) fermions with heavy gauge bosons and heavy (or mirror) fermions. In this work we will present the impact of the new flavour structure of T-parity models on flavour violations in leptonic sector.
The one-loop contributions to the branching ratios for leptonic tau decays are calculated in the CP conserving 2HDM(II). We found that these one-loop contributions, involving both neutral and charged Higgs bosons, dominate over the tree-level H^+ exchange, the latter one being totally negligible for the decay into electron. The analysis is focused on large tanbeta enhanced contributions to the considered branching ratios. We derive a simple analytical expression for the one-loop contribution which holds in this case. We show that the leptonic branching ratios of tau are complementary to the Hi…
Recent data from the ATLAS and CMS detectors at the Large Hadron Collider at CERN give a hint of possible violation of flavor in the leptonic decays of the Higgs boson. In this work we analyze the flavor violating leptonic decays $H^0_1\to l_i \bar l_j$ ($i\neq j$) within the framework of an MSSM extension with a vectorlike leptonic generation. Specifically we focus on the decay mode $H^0_1\to μτ$. The analysis is done including tree and loop contributions involving exchange of $W, Z$, charge and neutral higgs and leptons and mirror leptons, charginos and neutralinos and sleptons and mirror sl…
In the Next-to-Minimal Supersymmetric Standard Model with the inverse seesaw mechanism to generate neutrino masses, the lightest sneutrino may act as a feasible dark matter candidate in vast parameter space. In this case, the smallness of the leptonic unitarity violation and the recent XENON-1T experiment can limit the dark matter physics. In particular, they set upper bounds of the neutrino Yukawa couplings $λ_ν$ and $Y_ν$. We study such effects by encoding the constraints in a likelihood function and carrying out elaborated scans over the parameter space of the theory with the Nested Samplin…
We investigate the semileptonic and leptonic B decays, B to D^{(*)} tau nu and B to tau nu in our multi-Higgs-doublet models, while keeping in mind the enhancement of the top forward-backward (FB) asymmetry (A^t_{FB}) at the Tevatron. In these models, the extra (pseudo)scalar bosons contribute to A^t_{FB} with large flavor-changing Yukawa couplings involving the top quark, but the contribution of the charged Higgs boson to A^t_{FB} is negligible. However, it may significantly affect B decays: especially, B to D^{(*)} tau nu and B to tau nu. We investigate the constraints on the B decays, based…
We demonstrate the potential of fully leptonic cascade decays of a heavy neutral Higgs boson through vectorlike leptons as a simultaneous probe for extended Higgs sectors and extra matter particles at the LHC. The processes we explore are unique in that their event topologies lead to di-boson-like leptonic final states with a lepton pair which does not reconstruct the mass of a gauge boson. By recasting existing $2\ell + E_T^{\rm miss}$ and $3/4\ell$ searches channels using run2 data from the LHC we obtain $\textit{model independent}$ bounds on the masses of heavy scalars and vectorlike lepton…
The new results on the muon anomalous magnetic moment (AMM) published by Fermilab in 2021, did not lead to a reduction of its long-pending deviation from the Standard Model (SM) value by more than 4$σ$. The explanation of this discrepancy by adding new particles to the theory puts many new physics models under tension when combined with the null results of the LHC direct searches for new particles. In this paper, we investigate the CP-violating Next-to-Minimal Supersymmetric extension of the SM (NMSSM) with and without an inverse seesaw mechanism. We compute the one-loop supersymmetric contrib…
We propose a flavor symmetric approach to unify the origin of dark matter (DM) with the non-zero $θ_{13}$ in the lepton sector. In this framework, breaking of a $U(1)$ flavor symmetry to a remnant $Z_2$ ensures the stability of the DM and gives rise to a modification to the existing $A_4$-based tri-bimaximal neutrino mixing to attain the required non-zero $\sin θ_{13}$. This results in a range of Higgs portal coupling of the DM which can be potentially accessible at various ongoing and future direct and collider search experiments.
We propose a minimal extension of the standard model by including a $U(1)$ flavor symmetry to establish a correlation between the relic abundance of dark matter, measured by WMAP and PLANCK satellite experiments and non-zero value of $\sin θ_{13}$ observed at DOUBLE CHOOZ, Daya Bay, RENO and T2K. The flavour symmetry is allowed to be broken at a high scale to a remnant $\mathcal{Z}_2$ symmetry, which not only ensures the stability to the dark matter, but also gives rise to a modification to the existing $A_4$-based tri-bimaximal neutrino mixing. This deviation in turn suggests the required non…
We constrain some lepton flavor violating vertices in the context of the two Higgs doublet model type III, assuming that the lightest scalar Higgs mass $% m_{h^{0}} $is about $115 $GeV. Specifically, based on the $g-2 $muon factor and the decay width of$ μ\to eγ$,$ $the following quite general bounds are obtained:$ 7.62\times 10^{-4}\lesssim ξ_{μτ}^{2}\lesssim 4.44\times 10^{-2}, $ $ξ_{eτ}^{2}\lesssim 2.77\times 10^{-14}$. Additionally, based on the processes $τ\to μγ$, and $τ\to μμμ$, bounds on $ξ_{ττ} $and $ξ_{μμ} $are also gotten, such constraints on these parameters$ $still give enough roo…
In the Higgs Triplet Model and the neutrinophilic Two-Higgs-Doublet Model the observed neutrinos obtain mass from a vacuum expectation value which is much smaller than the vacuum expectation value of the Higgs boson in the Standard Model. Both models contain a singly charged Higgs boson (H^-) whose Yukawa coupling is directly related to the neutrino mass (i.e. a "neutrinophilic charged Higgs"). The partial decay widths of H^- into a charged lepton and a neutrino (H^- to l^- nu) depend identically on the neutrino masses and mixings in the two models. We quantify the impact of the recent measure…
This paper addresses the question of observability of neutral Higgs bosons through the leptonic decay in a two Higgs doublet model (2HDM). Both scalar and pseudoscalar Higgs bosons ($H,~A$) are considered. The model is set to type IV to enhance the leptonic decay. In such a scenario, a signal production process like $e^+e^- \to A^0H^0 \to ττμμ$ or $μμττ$ would provide a clear signal on top of the background in a di-muon invariant mass distribution far from the $Z$ boson pole mass. The analysis is based on a $τ$-id algorithm which preselects events if they have two $τ$ jets by requiring a hadro…
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 ran…
An extended Higgs sector may allow for new scalar particles well below the weak scale. In this work, we present a detailed study of a light scalar $S$ with enhanced coupling to leptons, which could be responsible for the existing discrepancy between experimental and theoretical determinations of the muon anomalous magnetic moment. We present an ultraviolet completion of this model in terms of the lepton-specific two-Higgs doublet model and an additional scalar singlet. We then analyze a plethora of experimental constraints on the universal low energy model, and this UV completion, along with t…
Electroweak precision observables allow stringent tests of the Standard Model at the quantum level and imply interesting bounds on the mass of the Higgs boson through higher-order loop effects. Very significant constraints come especially from the determination of the mass of the W boson and from the effective leptonic weak mixing angle. After shortly reviewing the status of theoretical computations of the W mass, the new calculation of two-loop corrections with closed fermion loops to the effective leptonic weak mixing angle is discussed in detail. The phenomenological implications of the new…
We present a detailed study of the central exclusive production of the Standard Model Higgs Boson in the WW decay channel at the LHC. We include estimates of the experimental acceptance, including that of the proposed proton tagging detectors at 220m and 420m around either ATLAS and / or CMS, and the level 1 trigger acceptances. We give first estimates of the photon-photon and glue-glue background processes in the semi-leptonic and fully-leptonic decay channels. We find that there will be a detectable signal for Higgs masses between 140 GeV and 200 GeV, and that the backgrounds should be contr…
Collider search for dark matter production has been performed over the years based on high pT standard model signatures balanced by large missing transverse energy. The mono-Z boson production with leptonic decay has a clean signature with the advantage that the decaying electrons and muons can be precisely measured. This signature not only enables reconstruction of the Z boson rest frame, but also makes possible recovery of the underlying production dynamics through the decaying lepton angular distribution. In this work, we exploit full information carried by the leptonic Z boson decays to se…
We explore the discovery potential of Higgs pair production at a 100 TeV collider via full leptonic mode. The same mode can be explored at the LHC when Higgs pair production is enhanced by new physics. We examine two types of fully leptonic final states and propose a partial reconstruction method. The reconstruction method can reconstruct some kinematic observables. It is found that the $m_{T2}$ variable determined by this reconstruction method and the reconstructed visible Higgs mass are important and crucial to discriminate the signal and background events. It is also noticed that a new vari…
