Boson Loops Research Articles

Multiphoton signatures as a probe of CP violation in extended Higgs sectors

We propose a novel signature with four-photon final states to probe CP-violating (CPV) extended Higgs sectors via ff¯→Z*→H1H2→4γ processes with H1,2 being additional neutral Higgs bosons. We focus on the nearly Higgs alignment scenario, in which the discovered Higgs boson almost corresponds to a neutral scalar state belonging to the isospin doublet field with the vacuum expectation value v≃246 GeV. We show that the branching ratios of H1,2→γγ can simultaneously be sizable when CPV phases in the Higgs potential are of order one due to the enhancement of charged-Higgs boson loops. Such branching ratios can be especially significant when the fermiophobic scenario is taken into account. As a simple example, we consider the general two Higgs doublet model, and demonstrate that the cross section for the four-photon process can be 0.1 fb at LHC with the masses of H1,2 to be a few 100 GeV in the Higgs alignment limit under the constraints from electric dipole moments (EDMs) and LHC Run-II data. We also illustrate that the searches for EDMs and diphoton resonances at high-luminosity LHC play complementary roles to explore CPV extended Higgs sectors. Published by the American Physical Society 2024

Monte-Carlo tool SANCphot for polarized γγ collision simulation

Our study of theoretical uncertainties for the four bosons processes at one-loop level including the case of the transverse polarization is presented. The calculations are based on helicity amplitudes approach for 4-boson SM interactions through a fermion and boson loops. The computation takes into account nonzero mass of loop particles. The obtained predictions are equally suitable for a wide range of energies and for arbitrary, including extreme, regions of the phase volume. Uncertainty estimates are received using the new Monte-Carlo tool SANCphot for γγ collision simulation with final states γγ, γZ, ZZ adapted for polarized γ beams. Program summaryProgram Title: sancphot-v1.01CPC Library link to program files:https://doi.org/10.17632/5sn9nywv2b.1Licensing provisions: LGPLProgramming language: Fortran, C, C++Nature of problem: Theoretical calculations at next-to-leading order in perturbation theory allow to compute higher precision amplitudes for Standard Model processes and decays, provided proper treatments of UV divergences and IR singularities are performed.Solution method: Numerical integration of the precomputed differential expressions for polarized photon-photon cross sections of four-boson interaction processes implemented as SANC modules [1].Additional comments including restrictions and unusual features: Uses subprograms Looptools [2], Cuba [3].The list of processes is limited to photon-photon, photon-Z and Z-Z collisions.

CP-violating 2HDMs emerging from 3-3-1 models

We investigate CP violating 2 Higgs doublet models as an effective theory emerging from models with an SU(3)L ⊗ U(1)X gauge symmetry. Because of the extension of the electroweak symmetry, a characteristic structure of Yukawa interactions appears with new CP violating phases at the electroweak scale. In this scenario, the charged Higgs boson loop provides dominant and sizable contributions to the neutron electric dipole moment (nEDM) at one-loop level. We find that the prediction of the nEDM can be slightly smaller than the current upper limit, mathcal{O} (10−26) e cm, with the mass of the charged Higgs boson and new CP violating phases to be a few hundred GeV and mathcal{O} (1), respectively, under the constraints from the meson mixings, the B → Xsγ decay and current LHC data.

Lepton anomalous magnetic moment with singlet-doublet fermion dark matter in a scotogenic U(1)Lμ−Lτ model

We study an extension of the minimal gauged ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ model including three right-handed singlet fermions and a scalar doublet to explain the anomalous magnetic moments of muon and electron simultaneously. The presence of an in-built ${Z}_{2}$ symmetry under which the right-handed singlet fermions and $\ensuremath{\eta}$ are odd, gives rise to a stable dark matter candidate along with light neutrino mass in a scotogenic fashion. In spite of the possibility of having positive and negative contributions to muon and electron ($g\ensuremath{-}2$) respectively from vector boson and charged scalar loops, the minimal scotogenic ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ model cannot explain both muon and electron ($g\ensuremath{-}2$) simultaneously while being consistent with other experimental bounds. We then extend the model with a vectorlike lepton doublet which not only leads to a chirally enhanced negative contribution to electron ($g\ensuremath{-}2$) but also leads to the popular singlet-doublet fermion dark matter scenario. With this extension, the model can explain both electron and muon ($g\ensuremath{-}2$) while being consistent with neutrino mass, dark matter and other direct search bounds. The model remains predictive at high energy experiments like collider as well as low energy experiments looking for charged lepton flavor violation, dark photon searches, in addition to future ($g\ensuremath{-}2$) measurements.

Probing the CP structure of the top quark Yukawa coupling: Loop sensitivity versus on-shell sensitivity

The question whether the Higgs boson is connected to additional $CP$ violation is one of the driving forces behind precision studies at the Large Hadron Collider. In this work, we investigate the $CP$ structure of the top quark Yukawa interaction---one of the most prominent places for searching for New Physics---through Higgs boson loops in top quark pair production. We calculate the electroweak corrections including arbitrary $CP$ mixtures at next-to-leading-order in the Standard Model Effective Field Theory. This approach of probing Higgs boson degrees of freedom relies on the large $t\overline{t}$ cross section and the excellent perturbative control. In addition, we consider all direct probes with on-shell Higgs boson production in association with a single top quark or top quark pair. This allows us to contrast loop sensitivity versus on-shell sensitivity in these fundamentally different process dynamics. We find that loop sensitivity in $t\overline{t}$ production and on-shell sensitivity in $t\overline{t}H$ and $tH$ provide complementary handles over a wide range of parameter space.

Циркулярная поляризация γ-кванта в радиационном распаде H Þ`ffγ (II)

Within the framework of the Standard Model, the radiative decay channel of the Higgs boson into fermion-antifermion pair is investigated: H Þ` ff γ. Taking into account the fermion and W -boson loop diagrams an analytical expression for the decay width is obtained, the circular polarization of the γ-quanta is studied in dependence of the angle θ and invariant mass of the fermion pair.

Anatomy of Higgs boson decays into γγ and γZ within the electroweak chiral Lagrangian in the Rξ gauges

In this work we study the Higgs boson decays into two photons and into one photon and one $Z$ gauge boson within the context of the non-linear Effective Field Theory called the Electroweak Chiral Lagrangian. We present a detailed computation of the corresponding amplitudes to one-loop level in the covariant $R_\xi$ gauges. We assume that the fermionic loop contributions are as in the Standard Model and focus here just in the computation of the bosonic loop contributions. Our renormalization program and the anatomy of the various contributions participating in the $R_\xi$ gauges are fully explored. With this present computation we demonstrate the gauge invariance of the EChL result, not only for the case of on-shell Higgs boson, but also for the most general and interesting case of off-shell Higgs boson. We finally analyse and conclude on the special relevance of the Goldstone boson loops, in good agreement with the expected chiral loops behaviour in Chiral Lagrangians. We perform a systematic comparison with the corresponding computation of the Standard Model in the $R_\xi$ gauges and with the previous EChL results in the unitary gauge. This work represents the first computation within the EChL of these Higgs observables to one-loop in the most general $R_\xi$ gauges and with a full renormalization program description, not yet fully explored in the previous literature and which is different to the most frequently used in the linear Effective Field Theory (SMEFT).

Magnetic mass effect on the sphaleron energy

We elucidate a magnetic mass effect on a sphaleron energy that is crucial for baryon number preservation needed for successful electroweak baryogenesis. It is found that the sphaleron energy increases in response to the magnetic mass. As an application, we study the sphaleron energy and electroweak phase transition with the magnetic mass in a two-Higgs-doublet model. Although the magnetic mass can screen the gauge boson loops, it relaxes a baryon number preservation criterion more effectively, broadening the baryogenesis-possible region. Our findings would be universal in any new physics models as long as the gauge sector is common to the standard model.

Light (and darkness) from a light hidden Higgs

We examine light diphoton signals from extended Higgs sectors possessing (approximate) fermiophobia with Standard Model (SM) fermions as well as custodial symmetry. This class of Higgs sectors can be realized in various beyond the SM scenarios and is able to evade many experimental limits, even at light masses, which are otherwise strongly constraining. Below the WW threshold, the most robust probes of the neutral component are di and multi-photon searches. Utilizing the dominant Drell-Yan Higgs pair production mechanism and combining it with updated LHC diphoton data, we derive robust upper bounds on the allowed branching ratio for masses between 45 − 160 GeV. Furthermore, masses ≲ 110 GeV are ruled out if the coupling to photons is dominated by W boson loops. We then examine two simple ways to evade these bounds via cancellations between different loop contributions or by introducing decays into an invisible sector. This also opens up the possibility of future LHC diphoton signals from a light hidden Higgs sector. As explicit realizations, we consider the Georgi-Machacek (GM) and Supersymmetric GM (SGM) models which contain custodial (degenerate) Higgs bosons with suppressed couplings to SM fermions and, in the SGM model, a (neutralino) LSP. We also breifly examine the recent ∼ 3σ CMS diphoton excess at ∼ 95 GeV.

Resummation of Goldstone infrared divergences: A proof to all orders

The perturbative effective potential calculated in Landau gauge suffers from infrared problems due to Goldstone boson loops. These divergences are spurious and can be removed by a resummation procedure that amounts to a shift of the mass of soft Goldstones. We prove this to all loops using an effective theory approach, providing a compact recipe for the shift of the Goldstone mass that relies on the use of the method of regions to split soft and hard Goldstone contributions.

Radiative corrections to Higgs coupling constants in two Higgs doublet models

A pattern of deviations in the Standard Model (SM) like Higgs boson (h) couplings from their SM predictions depends on the structure of the Higgs sector and the Yukawa interaction. In particular, in Two Higgs Doublet Models (THDMs) with a softly-broken Z2 symmetry, different characteristic patterns of deviation in Yukawa coupling constants (hff‾) can be allowed depending on four types of Yukawa interactions. We calculate hff‾ coupling constants at the one-loop level in all the types of THDMs. Even if there is no deviation in the hff‾ couplings at the tree level, they can deviate from the SM predictions by a few percent due to extra Higgs boson loop contributions. We find that if the deviations in the gauge couplings hVV(V=Z,W) are found with an enough large to be measured at the International Linear Collider (ILC), the scale factors for the hff‾ couplings do not overlap among the THDMs with four types of Yukawa interactions even taking into account the radiative corrections. Therefore, in such a case, we can indirectly determine the type of the THDMs at the ILC even without information from direct searches of the additional Higgs bosons.

Enhancement of the H±W∓Z vertex in the three scalar doublet model

We compute one-loop induced trilinear vertices with physical charged Higgs bosons H± and ordinary gauge bosons, i.e., H±W∓Z and H±W∓γ, in the model with two active plus one inert scalar doublet fields under a Z2(unbroken) × $$ {\tilde{Z}}_2 $$ (softly-broken) symmetry. The Z2 and $$ {\tilde{Z}}_2 $$ symmetries are introduced to guarantee the stability of a dark matter candidate and to forbid the flavour changing neutral current at the tree level, respectively. The dominant form factor F Z of the H±W∓Z vertex can be enhanced by effects of extra scalar boson loop contributions. We find that, in such a model, |F Z |2 can be one order of magnitude larger than that predicted in two Higgs doublet models, under the constraints from vacuum stability, perturbative unitarity and the electroweak precision observables. In addition, the branching fraction of the H± → W±Z (H± → W±γ) mode can be of order 10 (1)% level when the mass of H± is below the top quark mass. Such a light H± is allowed by the so-called Type-I and Type-X Yukawa interactions which appear under the classification of the $$ \tilde{Z} $$ charge assignment of the quarks and leptons. We also calculate the cross sections for the processes H± → W±Z and H± → W±γ onset by the top quark decay t → H±b and electroweak H± production at the LHC.

Flavour dependent gauged radiative neutrino mass model

We propose a one-loop induced radiative neutrino mass model with anomaly free flavour dependent gauge symmetry: $\mu$ minus $\tau$ symmetry $U(1)_{\mu-\tau}$. A neutrino mass matrix satisfying current experimental data can be obtained by introducing a weak isospin singlet scalar boson that breaks $U(1)_{\mu-\tau}$ symmetry, an inert doublet scalar field, and three right-handed neutrinos in addition to the fields in the standard model. We find that a characteristic structure appears in the neutrino mass matrix: two-zero texture form which predicts three non-zero neutrino masses and three non-zero CP-phases from five well measured experimental inputs of two squared mass differences and three mixing angles. Furthermore, it is clarified that only the inverted mass hierarchy is allowed in our model. In a favored parameter set from the neutrino sector, the discrepancy in the muon anomalous magnetic moment between the experimental data and the the standard model prediction can be explained by the additional neutral gauge boson loop contribution with mass of order 100 MeV and new gauge coupling of order $10^{-3}$.

Impact of top-Higgs couplings on Di-Higgs production at future colliders

Measuring the Higgs-self coupling is one of the most crucial goals of the future colliders, such as the LHC Run-II and the ILC-based photon collider. Since the new physics can affects the di-Higgs production not only from the Higgs self-coupling but also from the top-Higgs coupling, we investigate the di-Higgs production in the presence of the non-standard top-Higgs coupling at the LHC and ILC-based photon collider given the recent Higgs data. Due to the changed interference behaviors of the top quark loops with itself or W boson loops, we find that the cross section of di-Higgs production at the LHC-14 TeV and ILC-500 GeV can be respectively enhanced up to nearly 3 and 2 times the SM predictions within 2σ Higgs data allowed parameter region.

Flavor Changing Top Quark Decay and Bottom-Strange Production in the Littlest Higgs Model with T-parity

Flavor changing effects on the processes t → ch, e+e− → bs̄, e+e− → bs̄h and pp → bs̄ in the LHT model are investigated in this paper. We calculate the one-loop level contributions from the T-parity odd mirror fermions and gauge bosons. The results show that the top quark rare decay t → ch in the LHT model can be significantly enhanced relative to that in the SM. The bs̄ production at linear colliders in the LHT model can enhance the SM cross section a lot and reach 0.1 fb in some parameter space allowed in the experiment. But the heavy gauge boson and mirror fermion loops have small contribution to the processes pp → bs̄ and e+e− → bs̄h. So the LHT effect on e+e− → bs̄ might be detected at future linear colliders, while it is too small to be seen for the e+e− → bs̄h and pp → bs̄ processes at future linear colliders and LHC.

Standard model light-by-light scattering in SANC: Analytic and numeric evaluation

In this paper we describe the implementation of the SM process $\gamma\gamma\to\gamma\gamma$ through a fermion and boson loops into the framework of SANC system. The computations of this process takes into account non-zero mass of loop particles. We briefly describe additional precomputation modules used for calculation of massive box diagrams. We present the covariant and helicity amplitudes for this process, some particular cases of $D_0$ and $C_0$ Passarino--Veltman functions and also numerical results of corresponding SANC module evaluation. Whenever possible, we compare the results with those existing in the literature.

Finite width induced modification to the electromagnetic form factors of spin-1 particles

The inclusion of the unstable features of a spin-1 particle, without breaking the electromagnetic gauge invariance, can be properly accomplished by including higher order contributions as done in the so-called fermion loop scheme (for the W gauge boson), and the boson loop scheme (for vector mesons). This induces a non trivial modification to the electromagnetic vertex of the particle, which must be considered in addition to any other contribution computed as stable particles. Considering the modified electromagnetic vertex, we obtain general expressions for the corresponding corrections to the multipoles as a function of the mass of the particles in the loop. For the W gauge boson no substantial deviations from the stable case is observed. For the rho and K* mesons the mass of the particles in the loop makes a significant effect, and can be comparable with corrections of different nature .

Exact renormalization group flow for ultracold Fermi gases in the unitary limit

We study the exact renormalization group flow for ultracold Fermi gases in the unitary regime. We introduce a pairing field to describe the formation of the Cooper pairs and take a simple ansatz for the effective action. A set of approximate flow equations for effective couplings including boson and fermionic fluctuations is derived. At some value of the running scale, the system undergoes a phase transition to a gapped phase. The values of the energy density, chemical potential, pairing gap and the corresponding proportionality constants relating the interacting and non-interacting Fermi gases are calculated. Standard mean-field results are recovered if we omit the boson loops.

Spontaneous chiral symmetry breaking in the massless linear sigma model by fermion and boson loop corrections

We study the effect of one-loop corrections from nucleon together with those from boson in the massless linear sigma model, where we perform the Coleman–Weinberg (CW) renormalization procedure. This renormalization procedure has a mechanism of spontaneous symmetry breaking due to radiative corrections in ϕ 4 theory. We apply this CW scheme to the system of fermions and bosons with chiral symmetry where the negative-mass term of bosons does not exist. Spontaneous chiral symmetry breaking is derived from the contribution of the fermion and boson loops which generates the masses of nucleon and scalar meson dynamically. We find that the renormalization scale plays an important role for the breaking of the symmetry between fermion and boson, and eventually for the chiral symmetry at the same time. In addition, we find that the naturalness restores by means of the introduction of the loop corrections from both fermion and boson. We obtain, thus, a stable renormalized effective potential in the chiral model for the first time. We study then the non-perturbative corrections with fermions and bosons in the Cornwall, Jackiw and Tomboulis (CJT) method. We derive the Schwinger–Dyson equations for nucleon and boson in the massless linear sigma model and compare the form of equations in the CJT method with that in the one-loop approximation with the CW renormalization procedure. Finally we apply this model to finite nuclei as an effective model with the chiral symmetry.

Static properties of nuclear matter within the Boson Loop Expansion

The use of the Boson Loop Expansion is proposed for investigating the static properties of nuclear matter. We explicitly consider a schematic dynamical model in which nucleons interact with the scalar–isoscalar σ meson. The suggested approximation scheme is examined in detail at the mean field level and at the one- and two-loop orders. The relevant formulas are provided to derive the binding energy per nucleon, the pressure and the compressibility of nuclear matter. Numerical results of the binding energy at the one-loop order are presented for Walecka’s σ-ω model in order to discuss the degree of convergence of the Boson Loop Expansion.