Loop-induced Decay Research Articles

One-loop expressions for h → l l̅γ in Higgs extensions of the Standard Model

Abstract A systematic study of one-loop contributions to the decay channels $h\rightarrow l\bar{l}\gamma$ with l = νe, μ, τ, e, μ, performed in Higgs extended versions of the Standard Model (SM), is presented in the ’t Hooft–Veltman gauge. Analytic formulas for one-loop form factors are expressed in terms of the logarithm and di-logarithmic functions. As a result, these form factors can be reduced to those relating to the loop-induced decay processes h → γγ, Zγ, confirming not only previous results using different approaches but also close relations between the three kinds of loop-induced Higgs decay rates. For phenomenological study, we focus on the two observables, namely the enhancement factors defined as ratios of the decay rates calculated between the Higgs extended versions and the SM, and the forward-backward asymmetries of fermions, which can be used to search for Higgs extensions of the SM. We show that direct effects of mixing between neutral Higgs bosons and indirect contributions of charged Higgs boson exchanges can be probed at future colliders.

QCD predictions for event-shape distributions in hadronic Higgs decays

We study the six classical event-shape observables in hadronic Higgs decays at next-to-leading order in QCD. To this end, we consider the decay of on-shell Higgs bosons to three partons, taking into account both the Yukawa-induced decay to b-quark pairs and the loop-induced decay to two gluons via an effective Higgs-gluon coupling. The results are discussed with a particular focus on the discriminative power of event shapes regarding these two classes of processes.

Loop-induced h → γγ, Zγ, gg decays in 3-Higgs doublet models

In this paper, we analyze the loop-induced decays of neutral Higgs boson [Formula: see text] into pairs of photons, gluons and [Formula: see text] in 3-Higgs Doublet Models (3HDMs), where all the doublets have nonzero vacuum expectation values. In the 3HDM, there are contributions to these decays from loops of charged scalars [Formula: see text] that are not present in the Standard Model. We find an enhancement in the channel [Formula: see text] with respect to the Standard Model prediction in some parameter region while respecting constraints from the measurements of [Formula: see text] at the LHC. The charged Higgs bosons [Formula: see text] lead to the enhancement of [Formula: see text] decay mode in some part of the parameter space of the 3HDM. Then, we discuss the correlations between the decay modes [Formula: see text] and [Formula: see text]. Moreover, we study Type-I and Type-Z of 3HDMs and find that these types of 3HDMs can be distinguished via only the gluonic decays, since the contributions of the [Formula: see text] loops are dominant to those of fermion loops. We also investigate the effects of the model parameters on these loop-induced decays. As an interesting phenomenological consequence, the 3HDM is dominantly governed by the parameters: two ratios of vacuum expectation values (VEVs); [Formula: see text], [Formula: see text] and the mixing angles of the CP-even Higgs bosons, [Formula: see text] and [Formula: see text].

Extended Higgs boson sectors, effective field theory, and Higgs boson phenomenology

We consider the phenomenological implications of charged scalar extensions of the SM Higgs sector in addition to EFT couplings of this new state to SM matter. We perform a detailed investigation of modifications of loop-induced decays of the 125 GeV Higgs boson, which receives corrections from the propagating charged scalars alongside one-loop EFT operator insertions and demonstrate that the interplay of $H\to \gamma\gamma$ and $H\to Z\gamma$ decays can be used to clarify the additional states phenomenology in case a discovery is made in the future. In parallel, EFT interactions of the charged Higgs can lead to a decreased sensitivity to the virtual presence of charged Higgs states, which can significantly weaken the constraints that are naively expected from the precisely measured $H\to \gamma\gamma$ branching ratio. Again $H\to Z\gamma$ measurements provide complementary sensitivity that can be exploited in the future.

Neutral Higgs boson decays H→Zγ,γγ in 3-3-1 models

The significance of new physics appearing in the loop-induced decays of neutral Higgs bosons into pairs of dibosons $\gamma\gamma$ and $Z\gamma$ will be discussed in the framework of the 3-3-1 models based on a recent work~\cite{Okada:2016whh}, where the Higgs sector becomes effectively the same as that in the two Higgs doublet models (2HDM) after the first symmetry breaking from $SU(3)_L$ scale into the electroweak scale. For large $SU(3)_L$ scale $v_3\simeq10$ TeV, dominant one-loop contributions to the two decay amplitudes arise from only the single charged Higgs boson predicted by the 2HDM, leading to that experimental constraint on the signal strength $\mu^{331}_{\gamma\gamma}$ of the Standard Model-like Higgs boson decay $h\rightarrow \gamma\gamma$ will result in a strict upper bound on the signal strength $\mu^{331}_{Z\gamma}$ of the decay $h\rightarrow\, Z\gamma$. For a particular model with lower $v_3$ around 3 TeV, contributions from heavy charged gauge and Higgs bosons may have the same order, therefore may give strong destructive or constructive correlations. As a by-product, a deviation from the SM prediction $|\mu^{331}_{\gamma\gamma}-1| \le 0.04$ still allows $|\mu^{331}_{Z\gamma}-1|$ to reach values near 0.1. We also show that there exists an $CP$-even neutral Higgs boson $h^0_3$ predicted by the 3-3-1 models, but beyond the 2HDM, has an interesting property that the branching ratio Br$(h^0_3\rightarrow \gamma\gamma)$ is very sensitive to the parameter $\beta$ used to distinguish different 3-3-1 models.

Correlation between the decays h0 → γγ/gg in the MSSM with quark flavor violation

We study the loop-induced decays [Formula: see text] and [Formula: see text] in the Minimal Supersymmetric Standard Model (MSSM) with quark flavor violation (QFV), identifying [Formula: see text] with the Higgs boson with a mass of 125 GeV, where [Formula: see text] and [Formula: see text] are photon and gluon, respectively. We perform a MSSM parameter scan and a detailed analysis around a fixed reference point respecting theoretical constraints from vacuum stability conditions and experimental constraints, such as those from [Formula: see text]-meson data and electroweak precision data, as well as recent limits on Supersymmetric (SUSY) particle masses from LHC experiments. We find that (i) the relative deviation of the decay width [Formula: see text] from the Standard Model value, [Formula: see text], can be large and negative, [Formula: see text], (ii) the analogous deviation of [Formula: see text] is strongly correlated, [Formula: see text] for [Formula: see text], (iii) the relative deviation of the width ratio [Formula: see text] from the SM value, [Formula: see text], can be large (up to [Formula: see text]20%), (iv) the deviations can be large due to the up-type squark loop contributions, (v) the SUSY QFV parameters can have a significant effect on these deviations. Such large deviations can be observed at a future [Formula: see text] collider like ILC. Observation of the deviation patterns as shown in this study would favor the MSSM with flavor-violating squark mixings and encourage to perform further studies in this model.

Searching for the W\u03b3 decay of a charged Higgs boson

We study the prospects for charged Higgs boson searches in the Wγ decay channel. This loop-induced decay channel can be important if the charged Higgs is fermiophobic, particularly when its mass is below the WZ threshold. We identify useful kinematic observables and evaluate the future Large Hadron Collider sensitivity to this channel using the custodial-fiveplet charged Higgs in the Georgi-Machacek model as a fermiophobic benchmark. We show that the LHC with 300 fb−1 of data at 14 TeV will be able to exclude charged Higgs masses below about 130 GeV for almost any value of the SU(2)L-triplet vacuum expectation value in the model, and masses up to 200 GeV and beyond when the triplet vacuum expectation value is very small. We describe the signal simulation tools created for this analysis, which have been made publicly available.

Measurement ofCPviolation inBs0→ϕϕdecays

A measurement of the decay time dependent CP-violating asymmetry in $B_s^0 \to \phi\phi$ decays is presented, along with measurements of the $T$-odd triple-product asymmetries. In this decay channel, the CP-violating weak phase arises from the interference between $B_s^0$-$\bar{B}_s^0$ mixing and the loop-induced decay amplitude. Using a sample of proton-proton collision data corresponding to an integrated luminosity of $3.0\, fb^{-1}$ collected with the LHCb detector, a signal yield of approximately 4000 $B_s^0 \to \phi\phi$ decays is obtained. The CP-violating phase is measured to be ${\phi_s =-0.17\pm0.15\mathrm{\,(stat)}\pm0.03\mathrm{\,(syst)}}$ rad. The triple-product asymmetries are measured to be ${A_U=-0.003\pm0.017\mathrm{\,(stat)}\pm0.006\mathrm{\,(syst)}}$ and ${A_V=-0.017\pm0.017\mathrm{\,(stat)}\pm0.006\mathrm{\,(syst)}}$. Results are consistent with the hypothesis of CP conservation.

Dark matter versus h → γγ and h → γZ with supersymmetric triplets

The Triplet extension of the MSSM (TMSSM) alleviates the little hierarchy problem and provides a significant enhancement of the loop-induced diphoton rate of the lightest CP-even Higgs h. In this paper we pursue the analysis of the TMSSM Higgs phenomenology by computing for the first time the h into Z + gamma decay. Interestingly we find that the rates of loop-induced decays are correlated and their signal strengths can rise up to 40% - 60% depending on the channel. We furthermore study the dark matter phenomenology of the TMSSM. The lightest neutralino is a good dark matter candidate in two regions. The first one is related to the Higgs and Z resonances and the LSP is mostly Bino. The second one is achieved for a mass larger than 90 GeV and the LSP behaves as the well-tempered neutralino. An advantage of the triplet contribution is that the well-tempered neutralino can be a Bino-Triplino mixture, relieving the problem of achieving M_2 ~ M_1 in unified scenarios. The dark matter constraints strongly affect the Higgs phenomenology, reducing the potential enhancements of the diphoton and of the Z + photon channels by 20% at most. These enhancements are however larger than the MSSM ones. In the near future, complementarity of dark matter direct searches and collider experiments will be crucial to probe most of the parameter space where the neutralino is the dark matter candidate.

Measurements of Higgs Boson Properties using the ATLAS Detector

Measurements are presented of the production properties, couplings and spin- parity of the recently discovered Higgs-like boson using the decays into boson pairs, γγ, ZZ ∗ → 4� and WW ∗ → �ν�ν . The results shown here are based on the complete pp collision data sample recorded by the ATLAS experiment at the Large Hadron Collider (LHC) at centre-of-mass energies of √ s = 7 TeV and √ s = 8 TeV, and correspond to an integrated luminosity of about 25 fb −1 . Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions of loop-induced production and decay modes, are presented. The spin-parity hypothesis J P = 0 + , predicted for the Standard Model Higgs boson, is compared to alternative hypotheses (J P = 0 − 1, 1 + ,1 − and 2 + ). All measurements are consistent with the Standard Model expectations of the Higgs boson.

MicrOMEGAs_3: A program for calculating dark matter observables

micrOMEGAs is a code to compute dark matter observables in generic extensions of the standard model. This new version of micrOMEGAs is a major update which includes a generalization of the Boltzmann equations to accommodate models with asymmetric dark matter or with semi-annihilation and a first approach to a generalization of the thermodynamics of the Universe in the relic density computation. Furthermore a switch to include virtual vector bosons in the final states in the annihilation cross sections or relic density computations is added. Effective operators to describe loop-induced couplings of Higgses to two-photons or two-gluons are introduced and reduced couplings of the Higgs are provided allowing for a direct comparison with recent LHC results. A module that computes the signature of DM captured in celestial bodies in neutrino telescopes is also provided. Moreover the direct detection module has been improved as concerns the implementation of the strange “content” of the nucleon. New extensions of the standard model are included in the distribution. Program summaryTitle of program: micrOMEGAs3.Program obtainable from:http://lapth.cnrs.fr/micromegasComputers for which the program is designed and others on which it has been tested: PC, MacOperating systems under which the program has been tested : UNIX (Linux, Darwin)Programming language used: C and FortranMemory required to execute with typical data: 50 MB depending on the number of processes required.No. of processors used: 1Has the code been vectorized or parallelized: noNo. of bytes in distributed program, including test data: 70736 kBExternal routines/libraries used: noCPC Program Library subprograms used: CalcHEP, SuSpect, NMSSMTools, CPSuperH, LoopTools, HiggsBoundsCatalogue identifier of previous version: ADQR_v1_3Journal reference of previous version: Comput. Phys. Comm. 182 (2011) 842Does the new version supersede the previous version: yesNature of physical problem: Calculation of the relic density and direct and indirect detection rates of the lightest stable particle in a generic new model of particle physics.Method of solution: In numerically solving the evolution equation for the density of dark matter, relativistic formulae for the thermal average are used. All tree-level processes for annihilation and coannihilation of new particles in the model are included as well as some 3-body final states. The cross-sections for all processes are calculated exactly with CalcHEP after definition of a model file. The propagation of the charged cosmic rays is solved within a semi-analytical two-zone model.Reasons for the new version: There are many experiments that are currently searching for the remnants of dark matter annihilation and the relic density is determined precisely from cosmological measurements. In this version we add the computation of dark matter signals in neutrino telescopes, we generalize the Boltzmann equations so as to take into account a larger class of dark matter models and improve the precision in the prediction of the relic density for DM masses that are below the W mass. We compute the signal strength for Higgs production in different channels to compare with the results of the LHC.Summary of revisions:•Generalization of the Boltzmann equations to include asymmetric dark matter and semi-annihilations: the DM asymmetry is taken into account when computing direct/indirect detection rates.•Incorporating loop-induced decays of Higgs particles to two-photons and two-gluons, and computing the signal strength for Higgs production in various channels that can be compared to results from LHC searches.•New module for neutrino signature from DM capture in the Sun and the Earth•Annihilation cross sections for some selected 3-body processes in addition to the 2-body tree-level processes. The 3-body option can be included in the computation of the relic density and/or for annihilation of dark matter in the galaxy.•Possibility of using different tables for the effective degrees of freedom in the early Universe•Annihilation cross sections for the loop induced processes γγ and γZ0 in the NMSSM and the CPVMSSM•New function for incorporating DM clumps•New function to define the strange quark content of the nucleon•The LanHEP source code for new models is included•New models with scalar DM are included (Inert doublet model and model with Z3 symmetry)•New implementation of the NMSSM which uses the Higgs self-couplings and the particle spectrum calculated in NMSSMTools_4.1•New versions of spectrum generators used in the MSSM (Suspect_2.4.1) and in the CPVMSSM (CPsuperH2.3)•Extended routines for flavor physics in the MSSM•New facilities to compute DM observables independently of the model•Update in interface tools to read files produced by other codes, this allows easy interface to other codesTypical running time: 4 sUnusual features of the program: Depending on the parameters of the model, the program generates additional new code, compiles it and loads it dynamically.

The second Kaluza–Klein mode of CP-odd neutral Higgs boson in the minimal universal extra dimension model

Loop-induced decays of a neutral standard model (SM) Higgs boson into a pair of gluons or photons are very suppressed if the Higgs boson is heavy (≳500 GeV). In the minimal universal extra dimension model, these radiative decays can be significant for the second Kaluza–Klein (KK) mode of the CP-odd Higgs boson, χ(2). We find that the CP-even KK Higgs boson has vanishing decay rate of h(2)→gg at one-loop level: the h(2) production at the LHC is very suppressed. On the contrary, the process gg→χ(2)→γγ in an optimal scenario can be observed with manageable SM backgrounds at the LHC.

Bounds and decays of new heavy vector-like top partners

We study the phenomenology of new heavy vector-like fermions that couple to the third generation quarks via Yukawa interactions, covering all the allowed representations under the standard model gauge groups. We first review tree and loop level bounds on these states. We then discuss tree level decays and loop-induced decays to photon or gluon plus top. The main decays at tree level are to W b and/or Z and Higgs plus top via the new Yukawa couplings. The radiative loop decays turn out to be quite close to the naive estimate: in all cases, in the allowed perturbative parameter space, the branching ratios are mildly sensitive on the new Yukawa couplings and small. We therefore conclude that the new states can be observed at the LHC and that the tree level decays can allow to distinguish the different representations. Moreover, the observation of the radiative decays at the LHC would suggest a large Yukawa coupling in the non-perturbative regime.

Higgs mechanism and loop-induced decays of a scalar into twoZbosons

We discuss general on-shell couplings of a scalar with two $Z$ bosons using an operator analysis. In addition to the operator that originated from the Higgs mechanism, two dimension-five operators, one $CP$ even and one $CP$ odd, are generated only at the loop level. Simple formulas are derived for the differential decay distributions when the $Z$ pair subsequently decays into four leptons by computing the helicity amplitudes, from which it is shown the $CP$-odd operator merely induces a phase shift in the azimuthal angular distribution between the two decay planes of the $Z$ bosons. We also investigate new physics scenarios giving rise to loop-induced decays of a scalar into the $ZZ$ pair, and argue that the total decay width of such a scalar would be an order-of-magnitude smaller than that of a Higgs boson, should such decays be observed in the early running of the LHC. Therefore, the total decay width alone is a strong indicator of the Higgs nature, or the lack thereof, of a scalar resonance in $ZZ$ final states. In addition, we study the possibility of using the azimuthal angular distribution to disentangle effects among all three operators.

Rare meson decays into very light neutralinos

We investigate the bounds on the mass of the lightest neutralino from rare meson decays within the minimal supersymmetric standard model (MSSM) with and without minimal flavor violation. We present explicit formulas for the two-body decays of mesons into light neutralinos and perform the first complete calculation of the loop-induced decays of kaons to pions and light neutralinos and $B$ mesons to kaons and light neutralinos. We find that the supersymmetric branching ratios are strongly suppressed within the MSSM with minimal flavor violation, and that no bounds on the neutralino mass can be inferred from experimental data, i.e., a massless neutralino is allowed. The branching ratios for kaon and $B$ meson decays into light neutralinos may, however, be enhanced when one allows for nonminimal flavor violation. We find new constraints on the MSSM parameter space for such scenarios and discuss prospects for future kaon and $B$ meson experiments. Finally, we comment on the search for light neutralinos in monojet signatures at the Tevatron and at the LHC.

Radiative and Electroweak B Decays at the LHC

Rare loop-induced decays are sensitive to new physics in many Standard Model extensions. In this paper we discuss the potential of the LHC experiments to study the radiative penguin decays b → s γ and the electroweak penguin decays b → ℓ ℓ s . The experimental strategies are presented.

LHC semileptonic and radiative rare B decays program

Rare loop-induced decays are sensitive to New Physics in many Standard Model extensions. In this paper we discuss the reconstruction of the radiative penguin decays b → s γ and the electroweak penguin decay b → l l s at the LHC. The expected annual yields and B/S estimates are presented.

Probing the Randall-Sundrum geometric origin of flavor with lepton flavor violation

The anarchic Randall-Sundrum model of flavor is a low energy solution to both the electroweak hierarchy and flavor problems. Such models have a warped, compact extra dimension with the standard model fermions and gauge bosons living in the bulk, and the Higgs living on or near the TeV brane. In this paper we consider bounds on these models set by lepton flavor-violation constraints. We find that loop-induced decays of the form l{yields}l{sup '}{gamma} are ultraviolet sensitive and incalculable when the Higgs field is localized on a four-dimensional brane; this drawback does not occur when the Higgs field propagates in the full five-dimensional space-time. We find constraints at the few TeV level throughout the natural range of parameters, arising from {mu}-e conversion in the presence of nuclei, rare {mu} decays, and rare {tau} decays. A tension exists between loop-induced dipole decays such as {mu}{yields}e{gamma} and tree-level processes such as {mu}-e conversion; they have opposite dependences on the five-dimensional Yukawa couplings, making it difficult to decouple flavor-violating effects. We emphasize the importance of the future experiments MEG and PRIME. These experiments will definitively test the Randall-Sundrum geometric origin of hierarchies in the lepton sector at the TeV scale.

Distinguishing split supersymmetry in Higgs signals at the CERN Large Hadron Collider

We examine the possibility of detecting signals of split supersymmetry in the loop-induced decay $h\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ of the Higgs boson at the Large Hadron Collider, where charginos, as surviving light fermions of the supersymmetric spectrum, can contribute in the loop. We perform a detailed study of uncertainties in various parameters involved in the analysis, and thus the net uncertainty in the standard model prediction of the rate. After a thorough scan of the parameter space, taking all constraints into account, we conclude that it will be very difficult to infer about split supersymmetry from Higgs signals alone.

SDECAY: a Fortran code for the decays of the supersymmetric particles in the MSSM

We present the Fortran code SDECAY, which calculates the decay widths and branching ratios of all the supersymmetric particles in the Minimal Supersymmetric Standard Model, including higher order effects. Besides the usual two-body decays of sfermions and gauginos and the three-body decays of charginos, neutralinos and gluinos, we have also implemented the three-body decays of stops and sbottoms, and even the four-body decays of the stop; the important loop-induced decay modes are also included. The QCD corrections to the two-body decays involving strongly interacting particles and the dominant components of the electroweak corrections to all decay modes are implemented. Program summary Title of program: SDECAY Version 1.1a (March 2005) Catalogue identifier: ADVJ Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADVJ Program obtainable: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: none Computer for which the program is designed: Any with a Fortran77 system Operating systems under which the program has been tested: Linux, Unix Typical running time: A few seconds on modern personal computers and workstations Programming language used: Fortran77 No. of lines in distributed program, including test data, etc.: 59 621 No. of bytes in distributed program, including test data, etc.: 338 478 Distribution format: tar.gz Memory required to execute (with test data): 7.3 MB Distribution format: ASCII Nature of physical problem: Numerical calculation of the decay widths and branching ratios of supersymmetric particles in the Minimal Supersymmetric Standard Model (MSSM). The program calculates two-, three- and four-body decays and loop decays. It includes the SUSY-QCD corrections to two-body decays involving strongly interacting particles. The top-quark decays within the MSSM are evaluated as well. Method of solution: Two-dimensional numerical integration of the analytic formulae for the double differential decay widths of the three-body decays. The other decay widths are calculated analytically. Restrictions on the complexity of the problem: In the higher order decay modes the total decay widths of the virtually exchanged (s)particles are not included in their respective propagators. The higher order decays are calculated when the two-body decays are kinematically closed.