Higgs Yukawa Couplings Research Articles

Proton Decay and Gauge Coupling Unification in an Extended SU(5) GUT with 45D Higgs

Abstract We present a comprehensive study of an extended SU(5) grand unified theory (GUT) that incorporates a 45D Higgs representation to address the shortcomings of the minimal SU(5) GUT, such as the inability to generate realistic fermion mass hierarchies and insufficient proton stability. By considering a hierarchical mass spectrum for the scalar components of the 45D Higgs, we demonstrate that successful gauge coupling unification (GCU) can be achieved. The color octet scalar, color triplet scalar, and color antitriplet scalar play crucial roles in realizing GCU when their masses are significantly lighter than other components of the 45D Higgs. We focus on the proton decay channels mediated by the exchange of the color antitriplet scalar. Assuming that the 45D Higgs couples to all three generations of fermions, we determine the 45D Higgs Yukawa couplings with which the observed fermion mass matrices at low energies are realized. We calculate proton decay rates using the Yukawa couplings obtained from renormalization group evolutions and matching conditions at the GUT scale, thereby exploring the dependence of proton decay rates on model parameters. We find that the $p \rightarrow \nu \pi$ mode imposes the most stringent constraint on the mass of the color antitriplet scalar $M_{S_1}$. We also study the correlations between the lower bounds on $M_{S_1}$ derived from different proton decay modes.

QT spectrum for Higgs boson production via heavy quark annihilation at N3LL′+aN3LO

We study the transverse momentum (qT) spectrum of the Higgs boson produced via the annihilation of massive quarks (s, c, b) in proton-proton collisions. Using soft-collinear effective theory (SCET) and working in the five-flavor scheme, we provide predictions at three-loop order in resummed perturbation theory (N3LL′). We match the resummed calculation to full fixed-order results at next-to-next-to-leading order (NNLO), and introduce a decorrelation method to enable a consistent matching to an approximate N3LO (aN3LO) result. Since the b-quark initiated process exhibits large nonsingular corrections, it requires special care in the matching procedure and estimation of associated theoretical uncertainties, which we discuss in detail. Our results constitute the most accurate predictions to date for these processes in the small qT region and could be used to improve the determination of Higgs Yukawa couplings from the shape of the measured Higgs qT spectrum. Published by the American Physical Society 2024

Constraining lepton flavor violating Higgs couplings at the HL-LHC in the vector boson fusion channel

We explore the parameter space of lepton flavor violating (LFV) neutral Higgs Yukawa couplings with the muon and tau leptons that can be probed at the high-luminosity Large Hadron Collider (HL-LHC) via the vector boson fusion (VBF) Higgs production process. Our projected sensitivities for the Standard Model Higgs ($h$) LFV branching ratio $\text{Br}(h\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\tau})$ in the $pp\ensuremath{\rightarrow}hjj\ensuremath{\rightarrow}(h\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\tau})jj$ channel at the HL-LHC are contrasted with the current and future low-energy constraints from the anomalous magnetic moment and electric dipole moment of the muon, as well as with other LFV observables, such as $\ensuremath{\tau}\ensuremath{\rightarrow}3\ensuremath{\mu}$ and $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}$. We also study the LFV prospects of a generic beyond the Standard Model neutral Higgs boson ($H$) with a mass in the range of ${m}_{H}\ensuremath{\in}[20,800]\text{ }\text{ }\mathrm{GeV}$ and give the projected model-independent upper limits on the VBF production cross section of $Hjj$ times the branching ratio of $H\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\tau}$ at the HL-LHC. We interpret these results in the context of a two-Higgs doublet model as a case study.

Constraining the {mathcal {C}}{mathcal {P}} structure of Higgs-fermion couplings with a global LHC fit, the electron EDM and baryogenesis

{mathcal {C}}{mathcal {P}} violation in the Higgs couplings to fermions is an intriguing, but not yet extensively explored possibility. We use inclusive and differential LHC Higgs boson measurements to fit the {mathcal {C}}{mathcal {P}} structure of the Higgs Yukawa couplings. Starting with simple effective models featuring {mathcal {C}}{mathcal {P}} violation in a single Higgs–fermion coupling, we probe well-motivated models with up to nine free parameters. We also investigate the complementarity of LHC constraints with the electron electric dipole moment bound, taking into account the possibility of a modified electron Yukawa coupling, and assess to which extent {mathcal {C}}{mathcal {P}} violation in the Higgs–fermion couplings can contribute to the observed baryon asymmetry of the universe. Even after including the recent analysis of angular correlations in Hrightarrow tau ^+tau ^- decays, we find that a complex tau Yukawa coupling alone may be able to account for the observed baryon asymmetry, but with large uncertainties in the baryogenesis calculation. A combination of complex top and bottom quark Yukawa couplings yields a result four times larger than the sum of their separate contributions, but remains insufficient to account for the observed baryon asymmetry.

Off-Shell Probes of the Higgs Yukawa Couplings: Light Quarks and Charm

We review the present status and the future prospects for the measurements of the Higgs Yukawa couplings to light quarks and charm. A special focus is given to new proposed off-shell probes, which offer promising and complementary opportunities to test light quark Yukawas in triboson final states. Additionally, a new off-shell strategy to test the charm Yukawa coupling in the final state with two bosons plus a charm and a jet is considered. First estimates for the HL-LHC and the FCC-hh sensitivities on the channel are presented, showing encouraging results.

Methodologies to Measure the CP Structure of the Higgs Yukawa Coupling to Tau Leptons

One of the central goals of the Large Hadron Collider has been the search, and later the study, of the Higgs boson. Its coupling structure under charge conjugation and parity (CP) symmetries has been extensively investigated as a probe for new physics. This paper presents a review of the methods collected in the literature to access the CP structure of the Yukawa coupling of the Higgs boson to tau leptons at proton colliders. A new notation is introduced to classify already existing methods, highlighting their common features and favoring the investigation of new, more performing alternatives.

Measuring the electron Yukawa coupling via resonant s-channel Higgs production at FCC-ee

The Future Circular Collider (FCC-ee) offers the unique opportunity of studying the Higgs Yukawa coupling to the electron, y_mathrm {e}, via resonant s-channel production, mathrm {e^+e^-}rightarrow mathrm {H}, in a dedicated run at sqrt{s} = m_mathrm {H}. The signature for direct Higgs production is a small rise in the cross sections for particular final states, consistent with Higgs decays, over the expectations for their occurrence due to Standard Model (SM) background processes involving mathrm {Z}^*, gamma ^*, or t-channel exchanges alone. Performing such a measurement is remarkably challenging for four main reasons. First, the low value of the e^pm mass leads to a tiny y_mathrm {e} coupling and correspondingly small cross section: sigma _mathrm {eerightarrow H} propto m_mathrm {e}^2 = 0.57 fb accounting for initial-state gamma radiation. Second, the mathrm {e^+e^-} beams must be monochromatized such that the spread of their centre-of-mass (c.m.) energy is commensurate with the narrow width of the SM Higgs boson, varGamma _mathrm {H} = 4.1 MeV, while keeping large beam luminosities. Third, the Higgs mass must also be known beforehand with a few-MeV accuracy in order to operate the collider at the resonance peak, sqrt{s} = m_mathrm {H}. Last but not least, the cross sections of the background processes are many orders-of-magnitude larger than those of the Higgs decay signals. A preliminary generator-level study of 11 Higgs decay channels using a multivariate analysis, which exploits boosted decision trees to discriminate signal and background events, identifies two final states as the most promising ones in terms of statistical significance: mathrm {H}rightarrow gg and mathrm {H}rightarrow mathrm {W}mathrm {W}^*!rightarrow ell nu + 2 jets. For a benchmark monochromatization with 4.1-MeV c.m. energy spread (leading to sigma _mathrm {eerightarrow H} = 0.28 fb) and 10 ab^{-1} of integrated luminosity, a 1.3sigma signal significance can be reached, corresponding to an upper limit on the e^pm Yukawa coupling at 1.6 times the SM value: |y_mathrm {e}|<1.6|y^mathrm {textsc {sm}}_mathrm {e}| at 95% confidence level, per FCC-ee interaction point per year. Directions for future improvements of the study are outlined.

Electric dipole moment constraints on CP-violating heavy-quark Yukawas at next-to-leading order

Electric dipole moments are sensitive probes of new phases in the Higgs Yukawa couplings. We calculate the complete two-loop QCD anomalous dimension matrix for the mixing of CP-odd scalar and tensor operators and apply our results for a phenomenological study of CP violation in the bottom and charm Yukawa couplings. We find large shifts of the induced Wilson coefficients at next-to-leading-logarithmic order. Using the experimental bound on the electric dipole moments of the neutron and mercury, we update the constraints on CP-violating phases in the bottom and charm quark Yukawas.

The attributes of the Spin-Charge-Family theory giving hope that the theory offers the next step beyond the Standard Model

The assumptions of the standard model are still waiting for an explanation. The spin-charge-family theory is promising in offering not only the explanation for the standard model postulates for quarks and leptons and vector and scalar gauge fields, but also for the cosmological observations, like there are the appearance of the dark matter, the matter-antimatter asymmetry, making several predictions. This theory assumes that the internal space of fermions (spins, handedness and all the charges) are described by the Clifford algebra in d > (13 + 1)-dimensional space, representing in d = (3 + 1) all by the standard model required properties of quarks and leptons and antiquarks and antileptons, with families included. Fermions interact with gravity only (the vielbeins and the two kinds of the spin connection fields), manifesting in d = (3 + 1) as all the vector gauge fields and the scalar gauge fields (higgs scalars and Yukawa couplings). In this talk I overview shortly the achievements of the spin-charge-family theory so far, explaining in particular the new way of the second quantization of fermions, offered by the description of the internal space of fermions with the anticommuting Clifford algebra objects of the odd character.

More light on Higgs flavor at the LHC: Higgs boson couplings to light quarks through h+γ production

Higgs production in association with a photon at hadron colliders is a rare process, not yet observed at the LHC. We show that this process is sensitive to significant deviations of Higgs couplings to first- and second-generation SM quarks (particularly the up type) from their SM values, and we use a multivariate neural network analysis to derive the prospects of the High Luminosity LHC to probe deviations in the up and charm Higgs Yukawa couplings through $h+\ensuremath{\gamma}$ production.

Refinements of the bottom and strange MSSM Higgs Yukawa couplings at NNLO

We extend the already existing two-loop calculation of the effective bottom-Yukawa coupling in the MSSM. In addition to the resummation of the dominant corrections for large values of tgbeta , we include the subleading terms related to the trilinear Higgs coupling A_b and contributions induced by the electroweak gauge couplings. This calculation has been extended to the NNLO corrections to the MSSM strange-Yukawa coupling. Our analysis leads to residual theoretical uncertainties of the effective Yukawa couplings at the per-cent level.

Hidden signals of new physics within the Yukawa couplings of the Higgs boson

The Large Hadron Collider (LHC) has measured the Higgs boson couplings with the heavier particles of the Standard Model (SM), and they seem to lay on a single line as function of the particle mass, as predicted in the SM. However a complete test of this property must involve the lighter generations, and the coming measurements at LHC, or future colliders, may reveal hidden patterns associated with physics beyond the SM. In renormalizable multi-Higgs models, the Higgs-fermion couplings could still be linear, but they could lay on multiple lines. Then, the angle subtended by these lines, with respect to the SM line, can be used to characterize different models, as it is shown here for the Two-Higgs doublet Model (2HDM). Models where fermion masses arise from higher-dimensional operators, may also result in large deviations from the SM values for the Higgs couplings, which would show an irregular pattern as a function of the fermion masses. In the case of neutrino masses, when they arise from the see-saw mechanism, one finds that the Higgs Yukawa couplings will show a non-linear mass relation.

Probing unification with precision Higgs physics

We propose a novel approach of probing grand unification through precise measurements on the Higgs Yukawa couplings at the LHC. This idea is well motivated by the appearance of effective operators not suppressed by the mass scale of unification ${M}_{\mathrm{U}}$ in realistic models of unification with the minimal structure of Yukawa sector. Such operators modify the Higgs Yukawa couplings in correlated patterns at scale ${M}_{\mathrm{U}}$ that hold up to higher-order corrections. The coherences reveal a feature that, the deviation of tau Yukawa coupling relative to its standard model value at the weak scale is the largest one among the third-generation Yukawa couplings. This feature, if verified by the future LHC, can serve as a hint of unification.

Natural top-bottom mass hierarchy in composite Higgs models

We consider composite two-Higgs doublet models based on gauge-Yukawa theories with strongly interacting fermions generating the top-bottom mass hierarchy. The model features a single "universal" Higgs-Yukawa coupling, $ g $, which is identified with the top quark $ g\equiv g_t \sim \mathcal{O}(1) $. The top-bottom mass hierarchy arises by soft breaking of a $ \mathbb{Z}_2 $ symmetry by a condensate of strongly interacting fermions. A mass splitting between vector-like masses of the confined techni-fermions controls this top-bottom mass hierarchy. This mechanism can be present in a variety of models based on vacuum misalignment. For concreteness, we demonstrate it in a composite two-Higgs scheme.

Where are the next Higgs bosons?

Simple symmetry arguments applied to the third generation lead to a prediction: there exist new sequential Higgs doublets with masses of order $\lesssim 5 $ TeV, with approximately universal Higgs-Yukawa coupling constants, $g\sim 1$. This is calibrated by the known Higgs boson mass, the top quark Higgs-Yukawa coupling, and the $b$-quark mass. A new massive weak-isodoublet, $H_b$, coupled to the $b$-quark with $g\sim 1$ is predicted, and may be accessible to the LHC at $13$ TeV, and definitively at the energy upgraded LHC of $26$ TeV. The extension to leptons generates a new $H_\tau$ and a possible $H_{\nu_\tau}$ doublet. The accessibility of the latter depends upon whether the mass of the $\tau$-neutrino is Dirac or Majorana.

Hto boverline{b}j at next-to-next-to-leading order accuracy

We present the calculation of the decay Hto boverline{b}j at next-to-next-to-leading order (NNLO) accuracy in QCD. We treat the bottom quarks as massless with a non-zero Higgs Yukawa coupling yb. We consider contributions in which the Higgs boson couples directly to bottom quarks, i.e. our predictions are accurate to order mathcal{O}left({alpha}_s^3{y}_b^2right) . We calculate the various components needed to construct the NNLO contribution, including an independent calculation of the two-loop amplitudes. We compare our results for the two-loop amplitudes to an existing calculation finding agreement. We present additional checks on our two-loop expression using the known infrared factorization properties as the emitted gluon becomes soft or collinear. We use our results to construct a Monte Carlo implementation of Hto boverline{b}j and present jet rates and differential distributions in the Higgs rest frame using the Durham jet algorithm.

Composite Higgs and leptoquarks from a simple group

We propose a composite grand unified theory to study the anomalies in the semileptonic B decays. We show a simple group containing the custodial and Standard Model gauge symmetries, that can deliver a set of composite pseudo Nambu-Goldstone bosons: the Higgs, a colorless SU(2)L-fourplet and three leptoquarks: a triplet and two doublets. We give a description in terms of an effective theory of resonances. By assuming anarchic partial compositeness of the Standard Model fermions, we find representations for the composite fermions that allow to obtain the Higgs Yukawa couplings, as well as leptoquark interactions explaining the deviations in {R}_{K^{left(*right)}}^{mu e} . We calculate the one-loop potential, we show that it can trigger electroweak symmetry breaking and we find a region of the parameter space that can reproduce the Standard Model spectrum. The model predicts leptoquark masses of order 0.4–1.3 TeV, corrections to some electroweak observables, with Z{b}_L{overline{b}}_L saturating the current bounds, and a very reach phenomenology at LHC. We also study the possibility of explaining {R}_{D^{left(*right)}}^{tau ell } .

Measurements of Higgs-boson decays to leptons with the ATLAS detector

Since its discovery in 2012, the Higgs boson has served as an important probe for precision measurements of the Standard Model and for searches for new physics beyond the Standard Model. One major goal of the LHC is the precise measurement of the Higgs Yukawa couplings to fermions. The latest ATLAS results of measurements of the Higgs boson decaying to leptons are presented, namely the cross-section measurement of the Higgs boson decay to two tau leptons and the searches for the di-muon decay and lepton-flavour-violating decays of the Higgs boson.

Electric dipole moment constraints on CP-violating light-quark Yukawas

Nonstandard CP violation in the Higgs sector can play an essential role in electroweak baryogenesis. We calculate the full two-loop matching conditions of the standard model, with Higgs Yukawa couplings to light quarks modified to include arbitrary CPviolating phases, onto an effective Lagrangian comprising CP-odd electric and chromoelectric light-quark (up, down, and strange) dipole operators. We find large isospin-breaking contributions of the electroweak diagrams. Using these results, we obtain significant constraints on the phases of the light-quark Yukawas from experimental bounds on the neutron and mercury electric dipole moments.

Constraints and implications on Higgs FCNC couplings from precision measurement of Bs→μ+μ− decay

We study constraints and implications of the recent LHCb measurement of ${\cal B}(B_s \to \mu^+\mu^-)$ for tree-level Higgs-mediated flavor-changing neutral current (FCNC) interactions. Combined with experimental data on $B_s$ mass difference $\Delta m_s$, the $h \to \mu \tau$, and the $h \to \tau^+\tau^-$ decay branching ratios from the LHC, we find that the Higgs FCNC couplings are severely constrained. The allowed regions for $B_s \to \mu \tau$, $\tau\tau$ and $h \to sb$ decays are obtained. Current data allow large CP violation in the $h \to \tau^+ \tau^-$ decay. Consequences of the Cheng-Sher ansatz for the Higgs Yukawa couplings are discussed in some detail.