Spontaneous Breaking Of Electroweak Symmetry Research Articles

Bottom quark and tau lepton masses in a toy textrm{SU}(6) model

We study a toy textrm{SU}(6) model with the symmetry breaking pattern of the extended 331 symmetry of textrm{SU}(3)_c otimes textrm{SU}(3)_W otimes textrm{U}(1)_X. A “fermion-Higgs mismatching” symmetry breaking pattern is proposed for more realistic model building. Within such symmetry breaking pattern, only one Higgs doublet develops vacuum expectation value for the spontaneous electroweak symmetry breaking, and gives tree-level top quark mass. A natural VEV splittings in the 331 breaking Higgs fields gives tree-level masses to both bottom quark and tau lepton. The 125,textrm{GeV} SM-like Higgs boson discovered at the LHC can have Yukawa couplings to bottom quark and tau lepton as in the SM prediction, and this suggests the 331 symmetry breaking scale to be sim {{{mathcal {O}}}}(10),textrm{TeV}.

Searches for Resonant Scalar Boson Pair Production Using Run 2 LHC Proton-Proton Collision Data

The discovery of the Higgs boson in 2012 provided confirmation of spontaneous electroweak symmetry breaking as the mechanism by which fundamental particles gain mass and thus completed the Standard Model of particle physics. Additionally, it opened a new approach to searching for potential new particles. Many beyond the Standard Model theories predict new heavy particles that couple to the Higgs boson, leading to a resonant production mode of Higgs boson pairs. Other theories extend the Higgs sector by introducing additional scalar bosons that differ from the observed Higgs boson only by mass. The ATLAS and CMS Collaborations have searched for evidence of such processes using s=13 TeV Run 2 proton-proton collision data at the Large Hadron Collider. This review article summarizes the latest experimental results from searches for resonant production of pairs of Higgs bosons or additional Higgs-like scalar bosons at ATLAS and CMS.

Exploration of Extended Higgs Sectors with Run-2 Proton–Proton Collision Data at the LHC

One doublet of complex scalar fields is the minimal content of the Higgs sector in order to achieve spontaneous electroweak symmetry breaking and, in turn, to generate the masses of fundamental particles in the Standard Model. However, several theories beyond the Standard Model predict a nonminimal Higgs sector and introduce additional singlets, doublets or even higher-order weak isospin representations, thereby yielding additional Higgs bosons. With its high proton–proton collision energy (13 TeV during Run-2), the Large Hadron Collider opens a new window towards the exploration of extended Higgs sectors. This review article summarises the current state-of-the-art experimental results recently obtained in searches for new neutral and charged Higgs bosons with a partial or full Run-2 dataset.

Scalar and fermion on-shell amplitudes in generalized Higgs effective field theory

Beyond-the-standard-model (BSM) particles should be included in effective field theory in order to compute the scattering amplitudes involving these extra particles. We formulate an extension of Higgs effective field theory which contains an arbitrary number of scalar and fermion fields with arbitrary electric and chromoelectric charges. The BSM Higgs sector is described by using the nonlinear sigma model in a manner consistent with the spontaneous electroweak symmetry breaking. The chiral-order counting rule is arranged consistently with the loop expansion. The leading-order Lagrangian is organized in accord with the chiral-order counting rule. We use a geometrical language to describe the particle interactions. The parametrization redundancy in the effective Lagrangian is resolved by describing the on-shell scattering amplitudes only with the covariant quantities in the scalar/fermion field space. We introduce a useful coordinate (normal coordinate), which simplifies the computations of the on-shell amplitudes significantly. We show that the high-energy behaviors of the scattering amplitudes determine the ``curvature tensors'' in the scalar/fermion field space. The massive spinor--wave function formalism is shown to be useful in the computations of on-shell helicity amplitudes.

Spontaneous breaking of Weyl quadratic gravity to Einstein action and Higgs potential

We consider the (gauged) Weyl gravity action, quadratic in the scalar curvature ( tilde{R} ) and in the Weyl tensor ( {tilde{C}}_{mu nu rho sigma} ) of the Weyl conformal geometry. In the absence of matter fields, this action has spontaneous breaking in which the Weyl gauge field ωμ becomes massive (mass mω ∼ Planck scale) after “eating” the dilaton in the tilde{R} 2 term, in a Stueckelberg mechanism. As a result, one recovers the Einstein-Hilbert action with a positive cosmological constant and the Proca action for the massive Weyl gauge field ωμ. Below mω this field decouples and Weyl geometry becomes Riemannian. The Einstein-Hilbert action is then just a “low-energy” limit of Weyl quadratic gravity which thus avoids its previous, long-held criticisms. In the presence of matter scalar field ϕ1 (Higgs-like), with couplings allowed by Weyl gauge symmetry, after its spontaneous breaking one obtains in addition, at low scales, a Higgs potential with spontaneous electroweak symmetry breaking. This is induced by the non-minimal coupling {xi}_1{phi}_1^2tilde{R} to Weyl geometry, with Higgs mass ∝ ξ1/ξ0 (ξ0 is the coefficient of the tilde{R} 2 term). In realistic models ξ1 must be classically tuned ξ1 ≪ ξ0. We comment on the quantum stability of this value.

Higgs Sector with Spontaneous CP Violation in S(3) Standard Model

Conditions for spontaneous Charge-Parity (CP) violation in the scalar potential sector of general $S(3)$ Higgs-doublet model (3HDM) are analyzed. An analysis of the Higgs sector of the minimal $S(3)$-invariant extension of the Standard Model including CP violation arising from the spontaneous breaking of the electroweak symmetry is presented. This extended Higgs sector with three SU(2) doublets Higgs fields with complex vev's provides an interesting scenario to analyze the Higgs masses spectrum, trilinear self-couplings and CP violation. We present how the spontaneous electroweak symmetry breaking, coming from three $S(3)$ Higgs fields, gives an interesting scenario with nine physical Higgs and three Goldstone bosons, when spontaneous CP violation arises from the Higgs field $S(3)$ singlet $H_S$.

Asymptotically free four-fermion interactions and electroweak symmetry breaking

We investigate the fermions of the standard model without a Higgs scalar. Instead, we consider a non-local four-quark interaction in the tensor channel which is characterized by a single dimensionless coupling $f$. Quantization leads to a consistent perturbative expansion for small $f$. The running of $f$ is asymptotically free and therefore induces a non-perturbative scale $\Lambda_{ch}$, in analogy to the strong interactions. We argue that spontaneous electroweak symmetry breaking is triggered at a scale where $f$ grows large and find the top quark mass of the order of $\Lambda_{ch}$. We also present a first estimate of the effective Yukawa coupling of a composite Higgs scalar to the top quark, as well as the associated mass ratio between the top quark and the W boson.

Spontaneous Electro-Weak Symmetry Breaking and Cold DarkMatter

In the standard model, the weak gauge bosons and fermions obtainmass after spontaneous electro-weak symmetry breaking, which isrealized by one fundamental scalar field, namely the Higgs field.We study the simplest scalar cold dark matter modelin which the scalar cold dark matter also obtains mass byinteraction with the weak-doublet Higgs field, in the same way asthose of weak gauge bosons and fermions. Our study shows that thecorrect cold dark matter relic abundance within 3σuncertainty (0.093<Ωdmh2<0.129) andexperimentally allowed Higgs boson mass (114.4⩽mh⩽208 GeV)constrain the scalar dark matter mass within 48⩽mS⩽78 GeV. This result is in excellent agreement with the result of deBoer et al. (50~100 GeV). Such a kind of dark matterannihilation can account for the observed gamma rays excess(10σ) at EGRET for energies above 1 GeV in comparison withthe expectations from conventional Galactic models. We alsoinvestigate other phenomenological consequences of this model. Forexample, the Higgs boson decays dominantly into scalar cold darkmatter if its mass lies within 48~64 GeV.

Chiral freedom and electroweak symmetry breaking

Antisymmetric tensor fields with chiral couplings to quarks and leptons may induce spontaneous electroweak symmetry breaking in a model without a fundamental Higgs scalar. No microscopic local mass term for the chiral tensors or chirons is allowed by the symmetries and our model exhibits only dimensionless couplings. However, the chiral couplings are asymptotically free and therefore generate a mass scale where they grow large. We argue that at this scale mass terms for the chiral tensor fields are generated nonperturbatively---the chirons appear as new massive spin-one particles. Furthermore a scalar top-antitop condensate forms, giving mass to the weak gauge bosons and fermions. In this scenario the longstanding gauge hierarchy problem finds a solution similar to the mass generation in QCD. We compute the general form of the effective action for the chiral tensors and sketch several possibilities of their detection at LHC or through precision tests of the electroweak standard model.

Radiative electroweak symmetry breaking in the extra dimensions scenarios

We study radiative spontaneous electroweak symmetry breaking in the non-supersymmetric extra dimension scenarios of the standard model extension proposed by Antoniadis et al., Dienes et al. and Pomarol et al. In the framework of the multi-scale effective theory, by using the renormalization group method with an up-to-down viewpoint, we find that the effects of Kaluza-Klein excitations of bosons of the standard model can change the sign of the Higgs mass term of the standard model from positive to negative and break the electroweak symmetry. The critical scale for the electroweak phase transition to occur depends on the compactification scale (say 1.6 (2.0) TeV if the compactification scale is assumed to be 0.8 (1.5) TeV or so), and is insensitive to the mass of the Higgs particle. This radiative spontaneous symmetry breaking mechanism can work naturally in the extra dimension scenarios, and neither new particle contents beyond the standard model from the supersymmetry nor technicolor are necessary.

The Standard Model in its other phase

The standard model of particle physics is analyzed for the case of a Higgs potential not favoring spontaneous electroweak symmetry breaking to gain insight into the physics of the standard model. Electroweak breaking still takes place, and quarks and leptons still acquire masses but through bosonic technicolor. This ``other'' phase of the standard model exhibits interesting phenomena.

Experimental probes of localized gravity: On and off the wall

The phenomenology of the Randall-Sundrum model of localized gravity is analyzed in detail for the two scenarios where the standard model (SM) gauge and matter fields are either confined to a TeV scale 3-brane or may propagate in a slice of five dimensional anti--de Sitter space. In the latter instance, we derive the interactions of the graviton, gauge, and fermion Kaluza-Klein (KK) states. The resulting phenomenological signatures are shown to be highly dependent on the value of the 5-dimensional fermion mass and differ substantially from the case where the SM fields lie on the TeV-brane. In both scenarios, we examine the collider signatures for direct production of the graviton and gauge KK towers as well as their induced contributions to precision electroweak observables. These direct and indirect signatures are found to play a complementary role in the exploration of the model parameter space. In the case where the SM field content resides on the TeV-brane, we show that the CERN LHC can probe the full parameter space and hence will either discover or exclude this model if the scale of electroweak physics on the 3-brane is less than 10 TeV. We also show that spontaneous electroweak symmetry breaking of the SM must take place on the TeV-brane.

Nambu-Goldstone mechanism at finite temperature in the imaginary-time and real-time formalism

In the imaginary-time formalism of thermal field theory, and also in the real-time formalism, but by means of some redefined physical propagators for scalar bound states by diagonalization of four-point function matrices, we reexamine the Nambu-Goldstone mechanism of electroweak symmetry breaking in a one-generation fermion condensate scheme, based on the Schwinger-Dyson equation in the fermion bubble diagram approximation, and compare the obtained results. We have reached the conclusion that in both formalisms the Goldstone theorem of spontaneous electroweak symmetry breaking is rigorously true for the case of mass-degenerate two flavors of fermions and only approximately valid at low energy scales for the mass-nondegenerate case, in spite of the existence of some differences between the two formalisms in the imaginary parts of the denominators of the propagators for scalar bound states. When the two flavors of fermions have unequal nonzero masses, the induced possible fluctuation effect for the Higgs particle is negligible if the momentum cutoff in the zero temperature loops is large enough. All the results show physical equivalence of the two formalisms in the present discussed problems.

Can the triple Higgs self-coupling be measured at future colliders?

The experimental reconstruction of the Higgs self-energy potential is essential to a verification of the Higgs boson's rǒle in spontaneous electroweak symmetry breaking. The first step towards this goal, the measurement of the triple Higgs self-coupling, can possibly be accomplished at the next generation of linear colliders. Here we discuss the most promising channels at future hadron and e + e − colliders and present background studies to evaluate the feasibility of its measurement.

The case of a WW dynamical scalar resonance within a chiral effective description of the strongly interacting Higgs sector

We have studied the strongly interacting W L W L → W L W L I=L=0 partial wave amplitude making use of effective chiral Lagrangians. The Higgs boson is explicitly included and the N/D method is used to unitarize the amplitude. We recover the chiral perturbative expansion at next to leading order for low energies. The cases m H ≪4 πv and m H ≫4 πv are considered in detail. It is shown that in the latter situation a state appears with a mass ≲1 TeV. This state is dynamically generated through the strong interactions between the W L and is not responsible for the spontaneous electroweak symmetry breaking. However, its shape can be very similar to that of the m H ≲1 TeV case, which corresponds to a conventional heavy Higgs boson.

Supersymmetry and electroweak breaking from extra dimensions at the TeV scale

We analyze some features of the role that extra dimensions, of radius $R$ in the TeV$^{-1}$ range, can play in the soft breaking of supersymmetry and the spontaneous breaking of electroweak symmetry. We use a minimal model where the gauge and Higgs sector of the MSSM are living in the bulk of five dimensions and the chiral multiplets in a four-dimensional boundary. Supersymmetry is broken in the bulk by the Scherk-Schwarz mechanism and transmitted to the boundary by radiative corrections. The particle spectrum is completely predicted as a function of a unique $R$-charge. The massless sector corresponds to the pure Standard Model and electroweak symmetry is radiatively broken with a light Higgs weighing $\simlt$ 110 GeV. The $\mu$-problem is solved and Higgsinos, gauginos and heavy Higgses acquire masses $\sim 1/R$. Chiral sfermions acquire radiative squared-masses $\sim \alpha_i/R^2$. The effective potential is explicitly computed in the bulk of extra dimensions and some cosmological consequences can be immediately drawn from it. Gauge coupling running and unification is studied in the presence of Scherk-Schwarz supersymmetry breaking. The unification is similar to that in the supersymmetric theory.