Left-handed Quarks Research Articles

Topological susceptibility and axion potential in two-flavor superconductive quark matter

We study the potential of the axion, a, of Quantum Chromodynamics, in the two-flavor color superconducting phase of cold and dense quark matter. We adopt a Nambu-Jona-Lasinio-like model. Our interaction contains two terms, one preserving and one breaking the U(1)A symmetry: the latter is responsible of the coupling of axions to quarks. We introduce two quark condensates, hL and hR, describing condensation for left-handed and right-handed quarks respectively; we then study the loci of the minima of the thermodynamic potential, Ω, in the (hL,hR) plane, noticing how the instanton-induced interaction favors condensation in the scalar channel when the θ angle, θ=a/fa, vanishes. Increasing θ we find a phase transition where the scalar condensate rotates into a pseudoscalar one. We present an analytical result for the topological susceptibility, χ, in the superconductive phase, which stands both at zero and at finite temperature. Finally, we compute the axion mass and its self-coupling. In particular, the axion mass ma is related to the full topological susceptibility via χ=ma2fa2; hence our result for χ gives an analytical result for ma in the superconductive phase of high-density Quantum Chromodynamics. Published by the American Physical Society 2024

U(2) Is Right for Leptons and Left for Quarks.

We posit that the distinct patterns observed in fermion masses and mixings are due to a minimally broken U(2)_{q+e} flavor symmetry acting on left-handed quarks and right-handed charged leptons, giving rise to an accidental U(2)^{5} symmetry at the renormalizable level without imposing selection rules on the Weinberg operator. We show that the symmetry can be consistently gauged by explicit examples and comment on realizations in SU(5) unification. Via a model-independent analysis of a standard model viewed as an effective field theory, we find that selection rules due to U(2)_{q+e} enhance the importance of charged lepton flavor violation as a probe, where significant experimental progress is expected in the near future.

Chiral non-Abelian vortices and their confinement in three flavor dense QCD

We find chiral non-Abelian vortices having windings only in one of the diquark condensations of left-handed and right-handed quarks in the color-flavor locked phase of dense QCD. They are the minimum vortices carrying half color magnetic fluxes of those of non-Abelian semi-superfluid vortices (color magnetic flux tubes) and 1/6 quantized superfluid circulations of Abelian superfluid vortices. These vortices carry ${\mathbb C}P^2$ orientational moduli in the internal space corresponding to their fluxes. The ${\mathbb C}P^2$ moduli of two chiral non-Abelian vortices with chiralities opposite to each other are energetically favored to be aligned while those of a vortex and anti-vortex to be orthogonal, and then these vortices attract each other. They are attached by chiral domain walls in the presence of the mass and axial anomaly terms explicitly breaking axial and chiral symmetries. We numerically show that two chiral non-Abelian vortices with chiralities opposite to each other are connected by a chiral domain wall, consisting a mesonic bound state which is nothing but a non-Abelian semi-superfluid vortex. We also show that Abelian and non-Abelian axial vortices attached by chiral domain walls are all unstable to decay into a set of chiral non-Abelian vortices. Furthermore, we find that chiral non-Abelian vortices exhibit unique features: one is the so-called topological obstruction implying that unbroken symmetry generators in the bulk are not defined globally around the vortices, and the other is color non-singlet Aharonov-Bohm (AB) phases implying that quarks encircling these vortices can detect the colors of magnetic fluxes of them at infinite distances.

A twist on broken U(3) $$\times $$ U(3) supersymmetry

What symmetry breaking would be required for gauginos from a supersymmetric theory to behave like left-handed quarks of the Standard Model? Starting with a supersymmetric SU(3) $$\times $$ SU(3) $$\times $$ U(1) $$\times $$ U(1) gauge theory, the 18 adjoint-representation gauginos are replaced with 2 families of 9 gauginos in the (3,3*) representation of the group. After this explicit breaking of supersymmetry, two-loop quadratic divergences still cancel at a unification scale. Coupling constant unification is supported by deriving the theory from an SU(3) $$\times $$ SU(3) $$\times $$ SU(3) $$\times $$ SU(3) Grand Unified Theory (GUT). $${\hbox {Sin}}^2$$ of the Weinberg angle for the GUT is 1/4 rather than 3/8, leading to a lower unification scale than usually contemplated, $$\sim 10^9 \, \hbox {GeV}$$ . After spontaneous gauge symmetry breaking to SU(3) $$\times $$ SU(2) $$\times $$ U(1), the theory reproduces the main features of the Standard Model for two families of quarks and leptons, with gauginos playing the role of left-handed quarks and sleptons playing the role of the Higgs boson. An extension to the theory is sketched that incorporates the third family of quarks and leptons.

Modular symmetry origin of texture zeros and quark-lepton unification

The even weight modular forms of level $N$ can be arranged into the common irreducible representations of the inhomogeneous finite modular group $\Gamma_N$ and the homogeneous finite modular group $\Gamma'_N$ which is the double covering of $\Gamma_N$, and the odd weight modular forms of level $N$ transform in the new representations of $\Gamma'_N$. We find that the above structure of modular forms can naturally generate texture zeros of the fermion mass matrices if we properly assign the representations and weights of the matter fields under the modular group. We perform a comprehensive analysis for the $\Gamma'_3\cong T'$ modular symmetry. The three generations of left-handed quarks are assumed to transform as a doublet and a singlet of $T'$, we find six possible texture zeros structures of quark mass matrix up to row and column permutations. We present five benchmark quark models which can produce very good fit to the experimental data. These quark models are further extended to include lepton sector, the resulting models can give a unified description of both quark and lepton masses and flavor mixing simultaneously although they contain less number of free parameters than the observables.

Unified SU(4) theory for the RD(*) and RK(*) anomalies

We propose a chiral Pati-Salam theory based on the gauge group $SU(4)_C\times SU(2)_L\times SU(2)_R$. The left-handed quarks and leptons are unified into a fundamental representation of $SU(4)_C$, while right-handed quarks and leptons have a separate treatment. The deviations measured in the rare semi-leptonic decays $B\to D^{(*)} \tau\bar\nu$ are explained by a scalar leptoquark which couples to right-handed fields and is contained in the $SU(4)_C\times SU(2)_R$ breaking scalar multiplet. The measured deviation of lepton flavor universality in the rare decays $\bar B\to \bar K^{(*)}\ell^+\ell^-$, $\ell=\mu,e$ is explained via the $SU(4)_C$ leptoquark gauge boson. The model predicts a new sub-GeV scale sterile neutrino which participates in the anomaly and can be searched for in upcoming neutrino experiments. The theory satisfies the current most sensitive experimental constraints and its allowable parameter regions will be probed as more precise measurements from the LHCb and Belle II experiments become available.

Notes on anomalies, elliptic curves and the BS-D conjecture**In memory of P G O Freund.

We consider anomaly cancellation for gauge theories where the left-handed chiral multiplets are in higher representations. In particular, if the left-handed quarks and leptons transform under the triplet representation of and if the gauge group is compact then up to an overall scaling there is only one possible nontrivial assignment for the hypercharges if N = 3, and two if N = 9. Otherwise there are infinitely many. We use the Mordell–Weil theorem, Mazur’s theorem and the Cremona elliptic curve database which uses Kolyvagin’s theorem on the Birch Swinnerton-Dyer conjecture to prove these statements.

Chiral Imbalance in Hadron Matter: Its Manifestation in Photon Polarization Asymmetries

The possibility of the formation of a local parity breaking (LPB) in a quark-hadron medium is examined as a result of chiral symmetry violation, i.e, the appearance of difference between the average densities of right- and left-handed quarks in the fireball after heavy-ion collisions (HIC). Using the effective meson Lagrangian motivated by QCD extended to the chiral medium the properties of light scalar and pseudoscalar mesons are analyzed. It is establish that exotic decays of scalar mesons arise due to mixing of $\pi$ and $a_0$ vacuum states in the presence of chiral imbalance. The pion electromagnetic formfactor obtains a parity-odd supplement which generates a photon polarization asymmetry in pion polarizability. We conjecture that the above-mentioned properties of LPB can be revealed in experiments on LHC, RHIC, FAIR and NICA accelerators.

New Physics in {varvec{b rightarrow s ell ^+ ell ^-}} confronts new data on lepton universality

In light of the very recent updates on the R_K and R_{K^*} measurements from the LHCb and Belle collaborations, we systematically explore here imprints of New Physics in b rightarrow s ell ^+ ell ^- transitions using the language of effective field theories. We focus on effects that violate Lepton Flavour Universality both in the Weak Effective Theory and in the Standard Model Effective Field Theory. In the Weak Effective Theory we find a preference for scenarios with the simultaneous presence of two operators, a left-handed quark current with vector muon coupling and a right-handed quark current with axial muon coupling, irrespective of the treatment of hadronic uncertainties. In the Standard Model Effective Field Theory we select different scenarios according to the treatment of hadronic effects: while an aggressive estimate of hadronic uncertainties points to the simultaneous presence of two operators, one with left-handed quark and muon couplings and one with left-handed quark and right-handed muon couplings, a more conservative treatment of hadronic matrix elements leaves room for a broader set of scenarios, including the one involving only the purely left-handed operator with muon coupling.

Dark matter and flavor changing in the flipped 3-3-1 model

The flipped 3-3-1 model discriminates lepton families instead of the quark ones in normal sense, where the left-handed leptons are in two triplets plus one sextet while the left-handed quarks are in antitriplets, under SU(3)L. We investigate a minimal setup of this model and determine novel consequences of dark matter stability, neutrino mass generation, and lepton flavor violation. Indeed, the model conserves a noncommutative B−L symmetry, which prevents the unwanted vacua and interactions and provides the matter parity and dark matter candidates that along with normal matter form gauge multiplets. The neutrinos obtain suitable masses via a type I and II seesaw mechanism. The nonuniversal couplings of Z′ with leptons govern lepton flavor violating processes such as μ → 3e, μ → e overline{nu} μνe, μ-e conversion in nuclei, semileptonic τ → μ(e) decays, as well as the nonstandard interactions of neutrinos with matter. This Z′ may also set the dark matter observables and give rise to the LHC dilepton and dijet signals.

Left-handed color-sextet diquark in the kaon system

We investigate whether a color-sextet scalar diquark (${\bf H}_6$) coupling to the left-handed quarks contributes to the $\Delta S=2$ process. It is found that the box diagrams mediated by $W$ and ${\bf H}_6$ bosons have no contributions to $\Delta S=2$ when the limit of $m_t=0$ is used, and the flavor mixing matrices for diagonalizing quark mass matrices are introduced at the same time. When the heavy top-quark mass effects are taken into account, it is found that in addition to the $W-{\bf H}_6$ box diagrams significantly contributing to $\Delta S=2$, their effects can be as large as those from the ${\bf H}_6-{\bf H}_6$ box diagrams. Using the parameters that are constrained by the $K^0-\bar K^0$ mixing parameter $\Delta M_K$ and the Kaon indirect CP violation $\epsilon_K$, we find that the left-handed color-sextet diquark can lead to the Kaon direct CP violation being $Re(\epsilon'/\epsilon) \sim 0.4 \times 10^{-3}$. In the chosen scheme, although the diquark contribution to $K_L\to \pi^0 \nu \bar\nu$ is small, the branching ratio of $K^+ \to \pi^+ \nu \bar\nu$ can reach the current experimental upper bound.

Dihedral flavor group as the key to understand quark and lepton flavor mixing

We have studied the lepton and quark mixing patterns which can be derived from the dihedral group Dn in combination with CP symmetry. The left-handed lepton and quark doublets are assigned to the direct sum of a singlet and a doublet of Dn. A unified description of the observed structure of the quark and lepton mixing can be achieved if the flavor group Dn and CP are broken to Z2 × CP in neutrino, charged lepton, up quark and down quark sectors, and the minimal group is D14. We also consider another scenario in which the residual symmetry of the charged lepton and up quark sector is Z2 while Z2 × CP remains preserved by the neutrino and down quark mass matrices. Then D7 can give the experimentally favored values of CKM and PMNS mixing matrices.

Electric dipole moments from postsphaleron baryogenesis

We consider a model in which baryogenesis occurs at low scale, at a temperature below the electroweak phase transition. This model involves new diquark-type scalars which carry baryon number. Baryon number violation is introduced in the scalar potential, permitting $\Delta B=2$ violating process involving Standard Model quarks while avoiding stringent proton decay constraints. Depending on their quantum number assignment, the diquark-type scalars can couple to either right or left handed quarks, or to both. We show that this model can provide a viable explanation of the baryon asymmetry of the universe provided that the coupling to left handed quarks are present. However, the coexistence of couplings to left and right handed quarks introduces important phenomenological constraints on the model, such as radiative contributions to quark masses and the generation of electric dipole moments for nuclei, which probe the CP even and CP odd products of the relevant couplings constants, respectively. We demonstrate that the strongest such constraints arise from electric dipole moment measurements of the neutron and $^{199}$Hg. These constraints are sufficiently strong that, in the absence of an intricate flavor structure, baryogenesis must be dominated by the couplings of the new scalars to left handed quarks.

Chiral SU(4) explanation of the b→s anomalies

We propose a variant of the Pati-Salam model, with gauge group $SU(4)_C\times SU(2)_L\times U(1)_{Y'}$, in which the chiral left-handed quarks and leptons are unified into a $\underline{4}$ of $SU(4)_C$, while the right-handed quarks and leptons have quite a distinct treatment. The $SU(4)_C$ leptoquark gauge bosons can explain the measured deviation of lepton flavour universality in the rare decays: $\bar B \to \bar K^{(*)}\bar\ell\ell, \ell=\mu,e$ (taken as a hint of new physics). The model satisfies the relevant experimental constraints and makes predictions for the important $B$ and $\tau$ decays. These predictions will be tested at the LHCb and Belle II experiments when increased statistics become available.

The top-quark window on compositeness at future lepton colliders

In composite Higgs (CH) models, large mixings between the top quark and the new strongly interacting sector are required to generate its sizeable Yukawa coupling. Precise measurements involving top as well as left-handed bottom quarks therefore offer an interesting opportunity to probe such new physics scenarios. We study the impact of third-generation-quark pair production at future lepton colliders, translating prospective effective-field-theory sensitivities into the CH parameter space. Our results show that one can probe a significant fraction of the natural CH parameter space through the top portal, especially at TeV centre-of-mass energies.

Simultaneous interpretation of K and B anomalies in terms of chiral-flavorful vectors

We address the presently reported significant flavor anomalies in the Kaon and B meson systems such as the CP violating Kaon decay (ϵ′/ϵ) and lepton-flavor universality violation in B meson decays left({R}_{K^{left(*right)}}, {R}_{D^{left(*right)}}right) , by proposing flavorful and chiral vector bosons as the new physics constitution at around TeV scale. The chiral-flavorful vectors (CFVs) are introduced as a 63-plet of the global SU(8) symmetry, identified as the one-family symmetry for left-handed quarks and leptons in the standard model (SM) forming the 8-dimensional vector. Thus the CFVs include massive gluons, vector leptoquarks, and W′, Z′-type bosons, which are allowed to have flavorful couplings with left-handed quarks and leptons, and flavor-universal couplings to right-handed ones, where the latter arises from mixing with the SM gauge bosons. The flavor texture is assumed to possess a “minimal” structure to be consistent with the current flavor measurements on the K and B systems. Among the presently reported significant flavor anomalies in the Kaon and B meson systems (ϵ′/ϵ, {R}_{K^{left(*right)}}, {R}_{D^{left(*right)}} ), the first two ϵ′/ϵ and {R}_{K^{left(*right)}} anomalies can simultaneously be interpreted by the presence of CFVs; the {R}_{D^{left(*right)}} anomaly is predicted not to survive, due to the approximate SU(8) flavor symmetry. Remarkably, we find that as long as both of the ϵ′/ϵ and {R}_{K^{left(*right)}} anomalies persist beyond the SM, the CFVs predict the enhanced {K}^{+}to {pi}^{+}nu overline{nu} and {K}_Lto {pi}^0nu overline{nu} decay rates compared to the SM values, which will readily be explored by the NA62 and KOTO experiments, and they will also be explored in new resonance searches at the Large Hadron Collider.

Search for new physics in dijet angular distributions using proton\u2013proton collisions at sqrt{s}=13hbox {TeV} and constraints on dark matter and other models

A search is presented for physics beyond the standard model, based on measurements of dijet angular distributions in proton–proton collisions at sqrt{s}=13hbox {TeV}. The data collected with the CMS detector at the LHC correspond to an integrated luminosity of 35.9,text {fb}^{-1}. The observed distributions, corrected to particle level, are found to be in agreement with predictions from perturbative quantum chromodynamics that include electroweak corrections. Constraints are placed on models containing quark contact interactions, extra spatial dimensions, quantum black holes, or dark matter, using the detector-level distributions. In a benchmark model where only left-handed quarks participate, contact interactions are excluded at the 95% confidence level up to a scale of 12.8 or 17.5TeV, for destructive or constructive interference, respectively. The most stringent lower limits to date are set on the ultraviolet cutoff in the Arkani–Hamed–Dimopoulos–Dvali model of extra dimensions. In the Giudice–Rattazzi–Wells convention, the cutoff scale is excluded up to 10.1TeV. The production of quantum black holes is excluded for masses below 5.9 and 8.2TeV, depending on the model. For the first time, lower limits between 2.0 and 4.6TeVare set on the mass of a dark matter mediator for (axial-)vector mediators, for the universal quark coupling g_{mathrm {mathrm {q}}} =1.0.

A light Higgs at the LHC and the B-anomalies

After the Higgs discovery, the LHC has been looking for new resonances, decaying into pairs of Standard Model (SM) particles. Recently, the CMS experimen observed an excess in the di-photon channel, with a di-photon invariant mass of about 96 GeV. This mass range is similar to the one of an excess observed in the search for the associated production of Higgs bosons with the Z neutral gauge boson at LEP, with the Higgs bosons decaying to bottom quark pairs. On the other hand, the LHCb experiment observed a discrepancy with respect to the SM expectations of the ratio of the decay of B-mesons to K-mesons and a pair of leptons, {R}_{K^{left(ast right)}}=BRleft(Bto {K}^{left(ast right)}{mu}^{+}{mu}^{-}right)/BRleft(Bto {K}^{left(ast right)}{e}^{+}{e}^{-}right) . This observation provides a hint of the violation of lepton-flavor universality in the charged lepton sector and may be explained by the existence of a vector boson originating form a U{(1)_{L_{mu}}}_{-{L}_{{}_{tau }}} symmetry and heavy quarks that mix with the left-handed down quarks. Since the coupling to heavy quarks could lead to sizable Higgs di-photon rates in the gluon fusion channel, in this article we propose a common origin of these anomalies identifying a Higgs associated with the breakdown of the U{(1)_{L_{mu}}}_{-{L}_{{}_{tau }}} symmetry and at the same time responsible to the quark mixing, with the one observed at the LHC. We also discuss the constraints on the identification of the same Higgs with the one associated with the bottom quark pair excess observed at LEP.

Low scale composite Higgs model and 1.8 ∼2 TeV diboson excess

We consider a simple solution to explain the recent diboson excess observed by ATLAS and CMS Collaborations in models with custodial symmetry [Formula: see text]. The [Formula: see text] triplet vector boson [Formula: see text] with mass range of [Formula: see text] TeV would be produced through the Drell–Yan process with sizable diboson decay branching to account for the excess. The other [Formula: see text] bidoublet axial vector boson [Formula: see text] would cancel all deviations of electroweak obervables induced by [Formula: see text] even if the SM fermions mix with some heavy vector-like (composite) fermions which couple to [Formula: see text] (“nonuniversally partially composite”), therefore allows arbitrary couplings between each SM fermion and [Formula: see text]. We present our model in the “General Composite Higgs” framework with [Formula: see text] breaking at scale [Formula: see text] and demand the first Weinberg sum rule and positive gauge boson form factors as the theoretical constraints. We find that our model can fit the diboson excess very well if the left-handed SM light quarks, charged leptons and tops have zero, zero/moderately small and moderate/large composite components for reasonable values of [Formula: see text] and [Formula: see text]. The correlation between tree level [Formula: see text] parameter and the [Formula: see text] suggest a large [Formula: see text] contribution to [Formula: see text] and it is indeed a [Formula: see text] effect in our parameter space which provides a strong hint for our scenario if this diboson excess is confirmed by the [Formula: see text] TeV LHC Run II.

Anomaly-free models for flavour anomalies

We explore the constraints imposed by the cancellation of triangle anomalies on models in which the flavour anomalies reported by LHCb and other experiments are due to an extra U(1)^prime gauge boson Z^prime . We assume universal and rational U(1)^prime charges for the first two generations of left-handed quarks and of right-handed up-type quarks but allow different charges for their third-generation counterparts. If the right-handed charges vanish, cancellation of the triangle anomalies requires all the quark U(1)^prime charges to vanish, if there are either no exotic fermions or there is only one Standard Model singlet dark matter (DM) fermion. There are non-trivial anomaly-free models with more than one such ‘dark’ fermion, or with a single DM fermion if right-handed up-type quarks have non-zero U(1)^prime charges. In some of the latter models the U(1)^prime couplings of the first- and second-generation quarks all vanish, weakening the LHC Z^prime constraint, and in some other models the DM particle has purely axial couplings, weakening the direct DM scattering constraint. We also consider models in which anomalies are cancelled via extra vector-like leptons, showing how the prospective LHC Z^prime constraint may be weakened because the Z^prime rightarrow mu ^+ mu ^- branching ratio is suppressed relative to other decay modes.