Chiral Gauge Symmetry Research Articles

Chiral Nelson-Barr models: Quality and cosmology

It was recently shown that domain walls from the spontaneous breaking of CP symmetry are exactly stable, and must be inflated away to recover a viable cosmology. We investigate the phenomenological implications of this result in Nelson--Barr solutions of the strong CP problem. Combined with the upper bound on the scale of spontaneous CP breaking necessary to suppress contributions from dangerous, nonrenormalizable operators to $\bar{\theta}$, this puts an upper bound on the scale of inflation and the reheating temperature after inflation. Minimal Nelson--Barr models are therefore in tension with thermal leptogenesis, models of large-field inflation, or potential future observations of signals from topological remnants of an unrelated, subsequent phase transition. We study how extending Nelson--Barr models with a new, continuous chiral gauge symmetry can ameliorate this tension by forbidding the dangerous dimension-five operators. In particular, we show that gauging a linear combination of baryon number and hypercharge allows for an economic, anomaly-free extension of the minimal Nelson--Barr model, and discuss the phenomenological implications.

Spintronics with Weyl Semimetal

A microscopic theory was recently developed for electrical spin manipulations in magnetic Weyl semimetals. With handedness (or chirality) of Weyl fermions as a keyword, the results on spin-orbit torque, spin-transfer torque, and charge-induced torque are outlined in light of chiral asymmetry, chiral gauge symmetry, and the chiral anomaly, respectively.

Standard model-like D-brane models and gauge couplings

We systematically search intersecting D-brane models, which just realize the Standard Model chiral matter contents and gauge symmetry. We construct new classes of non-supersymmetric Standard Model-like models. We also study the gauge coupling constants of these models. The tree level gauge coupling is a function of the compactification moduli, the string scale, the string coupling and the winding numbers of D-branes. By tuning them, we examine whether the models can explain the experimental values of gauge couplings. As a result, we find that the string scale should be greater than 1014–15 GeV if the compactification scale and the string scale are of the same order.

Higgs boson and top-quark masses and parity-symmetry restoration

The recent ATLAS and CMS experiments show the first observations of a new particle in the search for the Standard Model Higgs boson at the LHC. We revisit the scenario that high-dimensional operators of fermions must be present due to the theoretical inconsistency of the fundamental cutoff (quantum gravity) with the parity-violating gauge symmetry of the Standard Model. Studying the four-fermion interaction of the third quark family, we show that at an intermediate energy threshold E≈4.27×103GeV for the four-fermion coupling being larger than a critical value, the spontaneous symmetry-breaking phase transits to the strong-coupling symmetric phase where composite Dirac fermions form fully preserving the chiral gauge symmetry of the Standard Model and the parity-symmetry is restored. Under this circumstance, we perform the standard analysis of renormalization-group equations of the Standard Model in the spontaneous symmetry-breaking phase. As a result, the Higgs boson mass mH≈126.7GeV and top-quark mass mt≈172.7GeV are obtained without drastically fine-tuning the four-fermion coupling.

Chiral lattice gauge theories and the strong coupling dynamics of a Yukawa-Higgs model with Ginsparg-Wilson fermions

The Yukawa-Higgs/Ginsparg-Wilson-fermion construction of chiral lattice gauge theories described in hep-lat/0605003 uses exact lattice chirality to decouple the massless chiral fermions from a mirror sector, whose strong dynamics is conjectured to give cutoff-scale mass to the mirror fermions without breaking the chiral gauge symmetry. In this paper, we study the mirror sector dynamics of a two-dimensional chiral gauge theory in the limit of strong Yukawa and vanishing gauge couplings, in which case it reduces to an XY model coupled to Ginsparg-Wilson fermions. For the mirror fermions to acquire cutoff-scale mass it is believed to be important that the XY model remain in its ``high temperature'' phase, where there is no algebraic ordering—a conjecture supported by the results of our work. We use analytic and Monte-Carlo methods with dynamical fermions to study the scalar and fermion susceptibilities, and the mirror fermion spectrum. Our results provide convincing evidence that the strong dynamics does not ``break the chiral symmetry (more precisely, that the mirror fermions do not induce algebraic ordering in two-dimensions), and that the mirror fermions decouple from the infrared physics.

Chiral gauge models for light sterile neutrinos

We construct a family of simple gauge models in which three sterile neutrinos become naturally light by virtue of a generalized seesaw mechanism involving a chiral gauge symmetry. Examples where the chiral gauge group is SU(5)', SU(7)', SU(3)' and/or their descendants are presented. A unified model based on SO(10) x SO(10)' which embeds many of these models is constructed wherein three light sterile neutrinos are just as natural as the three ordinary neutrinos. These gauge models have relevance to current neutrino oscillation data, including the LSND anomaly.

Simple model for (3+2) neutrino oscillations

We formulate a set of naturalness criteria for sterile neutrinos (ν′) to be light, needed for reconciling the LSND neutrino anomaly with the other neutrino data. A light sterile neutrino becomes as natural as the light active neutrinos if it carries quantum numbers of a chiral gauge symmetry broken at the TeV scale. The simplest such theory is shown to be an SU(2) gauge theory with the ν′ transforming as a spin 3/2 multiplet. We develop this model and show that it leads naturally to the phenomenologically viable (3+2) neutrino oscillation scheme. We also present next-to-minimal models for light sterile neutrinos based on a chiral U(1) gauge symmetry.

Simple model for (3+2) neutrino oscillations

We formulate a set of naturalness criteria for sterile neutrinos ( ν ′) to be light, needed for reconciling the LSND neutrino anomaly with the other neutrino data. A light sterile neutrino becomes as natural as the light active neutrinos if it carries quantum numbers of a chiral gauge symmetry broken at the TeV scale. The simplest such theory is shown to be an SU (2) gauge theory with the ν ′ transforming as a spin 3/2 multiplet. We develop this model and show that it leads naturally to the phenomenologically viable (3+2) neutrino oscillation scheme. We also present next-to-minimal models for light sterile neutrinos based on a chiral U (1) gauge symmetry.

Chiral gauged fermions on a lattice

The chiral fermion model with local multifermion interactions proposed in Nucl. Phys. B 486 (1997) 282 and Phys. Rev. D 61 (2000) 054502 processes an exact SU L (2) chiral gauge symmetry and SU L (2)⊗ U R (1) chiral flavour symmetry on a lattice and a plausible scaling region for the target chiral gauge theory in the continuum limit. Following the previous analysis of massive and massless fermion spectra in the scaling region, we compute the one-particle-irreducible coupling vertices between gauge field and fermions by the strong multifermion coupling expansion and analytical continuation of these vertex functions in the momentum space. We show a peculiar scenario that a massless fermion is SU L (2)-chirally gauged in the low energy and 15 non-degenerate massive Dirac fermions are SU L (2)-vectorially gauged at the lattice scale O (1/ a ). The Ward identities associated to the chiral gauge symmetry are realized by both the massless chiral fermion and massive Dirac fermions. These Ward identities protect the perturbative calculations in the small gauge coupling from hard gauge-symmetry breakings and lead to the normal gauge-invariant renormalization prescription. The vacuum functional is perturbatively computed by a continuum regularization scheme in 16 edges of Brillouin zones. We achieve the correct form of the gauge anomaly and U L (1) fermion-flavour singlet anomaly with the soft chiral symmetry breaking scale that is much smaller than the lattice scale. The residual breakings of chiral gauge symmetry after the gauge anomaly cancellation are eliminated in the normal gauge-invarinant renormalization prescription. We discuss the consistency of the scenario and the reasons for it to work for perturbative and non-perturbative gauge field.

Massless QED on random-block lattice

Massless QED is regularized using random-block lattice (RBL). Using naive fermion without explicitly breaking chiral symmetry or gauge symmetry in the action, it is shown that physical observables can avoid the effects of species doubling after averaging over an ensemble of RBL. For 2D QED, numerical results of dynamical fermion simulations using Hybrid Monte Carlo are in good agreement with the exact solutions of the Schwinger model in continuum.

Smooth non-Abelian bosonization

We present an extension of “smooth bosonization” to the non-Abelian case. We construct an enlarged theory containing both bosonic and fermionic fields which exhibits a local chiral gauge symmetry. A gauge fixing function depending on one real parameter allows us to interpolate smoothly between a purely fermionic and a purely bosonic representation. The procedure is, in the special case of bosonization, complementary to the approach based on duality.

Regularization of chiral gauge theories

In this paper we present an explicit two-loop calculation which shows that, as a consequence of the breaking of chiral gauge symmetry induced by the regularization, non-gauge invariant counterterms are present in the ghost sector of a chiral gauge theory. This occurrence prevents one from inverting the Faddeev-Popov procedure and removing the gauge fixing in numerical simulations.

A streamlined method for chiral fermions on the lattice

We discuss the use of renormalization counterterms to restore the chiral gauge symmetry in a lattice theory of Wilson fermions. We show that a large class of counterterms can be implemented automatically by making a simple modification to the fermion determinant.

Regularization of a chiral gauge theory: Evidence for a ghost counterterm

I report the result of an explicit two loop calculation which shows the presence of non-gauge invariant counterterms in the ghost sector of a chiral gauge theory. These counterterms are necessary to compensate the effects of the breaking of chiral gauge symmetry induced by the regularization.

Nonlocal regularization of the chiral Schwinger model

The recently developed technique of nonlocal regularization is applied to the two dimensional chiral Schwinger model, which is anomalous. It is shown that nonlocal regularization breaks the chiral gauge symmetry of the classical theory. However, the regularized theory belongs to a class of consistent theories considered by Jackiw and Rajaraman.

Chiral-gauge symmetry and Pauli-Villars regularization scheme

The Pauli-Villars procedure is used to regularize the quantum theory with a chiral-gauge symmetry. By use of the chiral-Schwinger model, which is anomalous, it is shown that the Pauli-Villars regularization fails to maintain gauge symmetry.

Some results from the breaking of chiral gauge symmetry

The fact that the breaking of chiral gauge symmetry in quantum field theory might be a genuine quantum effect for mass generation of gauge bosons is further studied in the lattice regularization of Weinberg-Salam model. We obtain the correct mass ratioMw = cos0wM z . Moreover, we discuss whether or not chiral fermions are confined in strong bare coupling region.

On the breaking of chiral gauge symmetry

It is conjectured that the lack of chiral gauge symmetry-preserving regulator is signalling a genuine quantum effect which breaks chiral gauge symmetries and generates masses for gauge bosons. This idea is applied to an SU(3) C ×SU(2) L ×U(1) Y model. It is shown that the dynamics of chiral fermions can generate masses for the W and Z bosons with the correct mass ratio. Chiral gauge theories without elementary scalars are found to be related to effective gauge theories with group element valued scalar fields. Furhtermore, massless fermions can exist in such theories.

Chiral (gauge) symmetry and regularizations

We show that the lack of the (global or local) chiral symmetry at the quantum level produces (1) a linearly divergent quark mass for massless QCD or (2) a quadratically divergent gauge boson mass for a chiral gauge theory by using lattice and Pauli-Villars regularizations, contrary to the usual claim that both are absent because of the chiral symmetry. We point out that the dimensional regularization, which is used to get the usual claim, fails to reproduce such dimensionful divergences, though the gauge invariance of the gauge boson propagator is broken by the dimensionless finite term. We conclude that dimensional regularization should not be used to discuss the divergent structure of some theory.

The breaking of chiral gauge symmetry and the fermionic mass matrix

The Weinberg-Salam model is studied in the lattice regularization scheme. By using the hopping parameter expansion, we show that SU L(2) ⊗ U Y(1) chiral gauge symmetry is broken completly if the fermionic mass matrix introduced is not diagonal, and the symmetry is broken to U cm (1) gauge symmetry if the fermionic mass matrix is diagonal.