Parity-violating Coupling Research Articles

Parity-violating trispectrum from Chern-Simons gravity

A potential source for parity violation in the Universe is inflation. The simplest inflationary models have two fields: the inflaton and graviton, and the lowest-order parity-violating coupling between them is dynamical Chern-Simons (dCS) gravity with a decay constant f. Here, we show that dCS imprints a parity-violating signal in primordial scalar perturbations. Specifically, we find that, after dCS amplifies one graviton helicity due to a tachyonic instability, the graviton-mediated correlation between two pairs of scalars develops a parity-odd component. This correlation, the primordial scalar trispectrum, is then transferred to the corresponding curvature correlator and thus is imprinted in both large-scale structure (LSS) and the cosmic microwave background (CMB). We find that the parity-odd piece has roughly the same amplitude as its parity-even counterpart, scaled linearly by the degree of gravitational circular polarization Πcirc ∼ √ε[h 2/(M Pl f)] ≤ 1, with ε the slow-roll parameter, H the inflationary Hubble scale, and the upper bound saturated for purely circularly-polarized gravitons. We also find that, in the collapsed limit, the ratio of the two trispectra contains direct information about the graviton's spin. In models beyond standard inflationary dCS, e.g. those with multiple scalar fields or superluminal scalar sound speed, there can be a large enhancement factor F ≳ 106 to the trispectrum. We find that an LSS survey that contains N modes linear modes would place an nσ constraint on Πcirc r of ∼ 0.04 (n/3)(106/F)(106/N modes)1/2 from the parity-odd galaxy trispectrum, for tensor-to-scalar ratio r. We also forecast for several spectroscopic and 21-cm surveys. This constraint implies that, for high-scale single-field inflation parameters, LSS can probe very large dCS decay constants f ≲ 4 × 109 GeV(3/n)(F/106)(N modes/106)1/2. Our result is the first example of a massless particle yielding a parity-odd scalar trispectrum through spin-exchange.

Exploring dark Z_d-boson in future large hadron-electron collider

The interaction between the dark U(1)_d sector with the visible Standard Model (SM) sector takes place through the kinetic mixing between the dark photon U(1)_d field Z_d^mu and the SM U(1)_Y gauge field B_mu . After the electroweak and U(1)_d symmetry breaking, the dark photon Z_d^mu acquires a mass and mixes with the SM neutral vector boson Z_mu . This mixing leads to parity-violating coupling between the Z_d^mu and SM. The coupling between the dark photon and SM can be explored in low energy phenomenology as well as in collider experiments. The Lorentz structure of dark photon interaction with SM fermions is explored in the proposed high energy future Large Hadron-electron collider, which would provide efficient energy and a clean environment using cross-section and asymmetries associated with polarisation observable of the dark photon in leptons decay. A chi ^2-analysis is performed to compare the strength of various variables for both the charge- and neutral-current processes. Based on this analysis, 90% confidence level (C.L.) contours in the varepsilon -m_{Z_d} and varepsilon -g_V plane are obtained to put limits on the Z_d^mu mass up to 100 GeV, coupling strength varepsilon and on the Lorentz structure of dark photon coupling with the SM fermions (g_V) at sqrt{s} approx 1.3 TeV.

Search for trilepton resonances from chargino and neutralino pair production in s=13 TeV pp collisions with the ATLAS detector

A search is performed for the electroweak pair production of charginos and associated production of a chargino and neutralino, each of which decays through an $R$-parity-violating coupling into a lepton and a $W$, $Z$, or Higgs boson. The trilepton invariant-mass spectrum is constructed from events with three or more leptons, targeting chargino decays that include an electron or muon and a leptonically decaying $Z$ boson. The analyzed dataset corresponds to an integrated luminosity of 139 fb$^{-1}$ of proton-proton collision data produced by the Large Hadron Collider at a center-of-mass energy of $\sqrt{s}$ = 13 TeV and collected by the ATLAS experiment between 2015 and 2018. The data are found to be consistent with predictions from the Standard Model. The results are interpreted as limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model. Limits are also set on the production of charginos and neutralinos for a Minimal Supersymmetric Standard Model with an approximate $B$-$L$ symmetry. Charginos and neutralinos with masses between 100 GeV and 1100 GeV are excluded depending on the assumed decay branching fractions into a lepton (electron, muon, or $\tau$-lepton) plus a boson ($W$, $Z$, or Higgs).

No chiral light bending by clumps of axion-like particles

Abstract We study the propagation of light in the presence of a parity-violating coupling between photons and axion-like particles (ALPs). Naively, this interaction could lead to a split of light rays into two separate beams of different polarization chirality and with different refraction angles. However, by using the eikonal method we explicitly show that this is not the case and that ALP clumps do not produce any spatial birefringence. This happens due to non-trivial variations of the photon’s frequency and wavevector, which absorb time-derivatives and gradients of the ALP field. We argue that these variations represent a new way to probe the ALP-photon coupling with precision frequency measurements.

Constraining R -parity-violating couplings in τ -processes at the LHC and in electroweak precision measurements

We find new limits on the nine ${\ensuremath{\lambda}}_{3jk}^{\ensuremath{'}}$ $R$-parity violating couplings of the minimal supersymmetric standard model, using Drell-Yan differential cross sections at the LHC and electroweak precision measurements from LEP and SLC. Specifically, limits on six of the nine ${\ensuremath{\lambda}}_{3jk}^{\ensuremath{'}}$-couplings, with $j=1$ or 2, are obtained using Drell-Yan data, providing the strongest bounds on three of these couplings. Four of the nine couplings are currently best constrained by electroweak data, which we reexamine here using a specifically lepton flavor-violating observable. The remaining two couplings are best constrained due to their contributions to neutrino masses, a bound which we update here. We also update previous limits on all ${\ensuremath{\lambda}}_{ijk}^{\ensuremath{'}}$-couplings using both electroweak data and neutrino mass bounds. A table of all current bounds on ${\ensuremath{\lambda}}_{ijk}^{\ensuremath{'}}$ is given in the Appendix.

Polarization of top and chargino from stop decay in natural SUSY

Top squark (stop) plays a crucial role in the naturalness of supersymmetry (SUSY) models, which has been extensively searched for in the LHC experiments. Due to the parity-violating couplings, top quark and chargino thus produced from stop decay are expected to be polarized. We investigate the polarization of top quark and chargino, from which we find that the mass differences between neutralino and stop/chargino can affect the degree of polarization of top quark/chargino in the stop decay. We then examine the top polarization effects on kinematics of stop decay in natural SUSY (NSUSY) at the LHC and the results show that several observables have the discriminating power for different polarized top quark at the LHC, which may be useful for testing the nature of stop couplings in NSUSY.

Limits on R -parity-violating couplings from Drell-Yan processes at the LHC

We find constraints on R-Parity Violating (RPV) couplings of the minimal supersymmetric standard model, using Drell-Yan differential cross sections at the LHC. Specifically, we look at the constraints on $\lambda'LQD^c$ couplings from monolepton and dilepton data published by ATLAS, with either electrons or muons in the final state. Out of the 18 RPV couplings to which the LHC is at least potentially sensitive by this technique, we find new limits on 12 (or 13) of them, for squarks masses above 1 (or 2) TeV. We also show that one can employ our techniques to achieve significantly stronger bounds at a high-luminosity upgrade of the LHC.

Search for B−L R -parity-violating top squarks in s=13 TeV pp collisions with the ATLAS experiment

A search is presented for the direct pair production of the stop, the supersymmetric partner of the top quark, that decays through an $R$-parity-violating coupling to a final state with two leptons and two jets, at least one of which is identified as a $b$-jet. The dataset corresponds to an integrated luminosity of 36.1 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of $\sqrt{s} = 13$ TeV, collected in 2015 and 2016 by the ATLAS detector at the LHC. No significant excess is observed over the Standard Model background, and exclusion limits are set on stop pair production at a 95% confidence level. Lower limits on the stop mass are set between 600 GeV and 1.5 TeV for branching ratios above 10% for decays to an electron or muon and a $b$-quark.

A new twist on top quark spin correlations

Top-antitop pairs produced at hadron colliders are largely unpolarized, but their spins are highly correlated. The structure of these correlations varies significantly over top production phase space, allowing very detailed tests of the Standard Model. Here, we explore top quark spin correlation measurement from a general perspective, highlighting the role of azimuthal decay angles. By taking differences and sums of these angles about the top-antitop production axis, the presence of spin correlations can be seen as sinusoidal modulations resulting from the interference of different helicity channels. At the LHC, these modulations exhibit nontrivial evolution from near-threshold production into the boosted regime, where they become sensitive to almost the entire QCD correlation effect for centrally produced tops. We demonstrate that this form of spin correlation measurement is very robust under full kinematic reconstruction, and should already be observable with high significance using the current LHC data set. We also illustrate some novel ways that new physics can alter the azimuthal distributions. In particular, we estimate the power of our proposed measurements in probing for anomalous color-dipole operators, as well as for broad resonances with parity-violating couplings. Using these methods, the 2012 run of the LHC may be capable of setting simultaneous limits on the top quark’s anomalous chromomagnetic and chromoelectric dipole moments at the level of 3 × 10−18 cm (0.03/m t ).

LargeNcexpansion and the parity-violatingπ,N,Δcouplings

In the limit of large N{sub c} we first consider the N{sub c} ordering of the various parity-violating {pi}, N, {delta} couplings. Then we derive the relations among these couplings and consistency relations from the stability of these couplings under the chiral loop corrections with and without the mass splitting between N and {delta}. Especially we find that h{sub {delta}}=-(3/{radical}(5))h{sub {pi}} in the large N{sub c} limit, which correctly reproduces the relative sign and magnitude of the Desplanques-Donoghue-Holstein values for these parity-violating couplings.

Polarized tops from stop decays at the LHC

In supersymmetric models, scalar top quarks, or stops, generically have parity-violating couplings to top quarks. As a result, tops produced in stop decays should be polarized. In this paper, we will argue that this effect may be observable at the LHC with realistic integrated luminosities, provided that one of the stops is copiously produced and can decay to a top and a neutralino. We define the ``effective'' stop mixing angle, which determines the degree of top polarization, and discuss the prospects for a measurement of this angle at the LHC. If some information about the neutralino mixing matrix is available, this measurement can be used to constrain the mixing angle in the stop sector, one of the most important ingredients in assessing the naturalness of electroweak symmetry breaking in the MSSM.

Parity-violating nuclear force as derived from QCD sum rules

Parity-violating nuclear force, as may be accessed from parity-violation studies in nuclear systems, represents an area of nonleptonic weak interactions that has been the subject of experimental investigations for several decades. In the simple meson-exchange picture, a parity-violating nuclear force may be parametrized as arising from the exchange of $\ensuremath{\pi},\ensuremath{\rho},\ensuremath{\omega}$, or other mesons with strong meson-nucleon coupling at one vertex and weak parity-violating meson-nucleon coupling at the other vertex. The QCD sum rule method allows for a fairly complicated, but nevertheless straightforward, leading-order loop-contribution determination of the various parity-violating $\mathrm{MNN}$ couplings starting from QCD (with the nontrivial vacuum) and Glashow-Salam-Weinberg electroweak theory. We continue our earlier investigation of the parity-violating $\ensuremath{\pi}\mathit{NN}$ coupling (by Henley, Hwang, and Kisslinger) to other parity-violating couplings. Our predictions are in reasonable overall agreement with the results estimated on phenomenological grounds, such as in the now classic paper of Desplanques, Donoghue, and Holstein, in the global experimental fit of Adelberger and Haxton, or the effective field theory thinking of Ramsey-Musolf and Page.

MeasuringZ′couplings at the CERN LHC

We study the properties of potential new ${Z}^{\ensuremath{'}}$ gauge bosons produced through the Drell-Yan mechanism at the Large Hadron Collider (LHC). Our analysis is performed using a fully differential next-to-leading-order QCD calculation with spin correlations, interference effects, and experimental acceptances included. We examine the distinguishability of different models and the feasibility of extracting general coupling information with statistical, residual scale, and current parton distribution function error estimates included. We extend a previous parametrization of ${Z}^{\ensuremath{'}}$ couplings to include parity-violating coupling combinations and introduce a convenient technique for simulating new gauge bosons on-peak using the concept of basis models. We illustrate our procedure using several example ${Z}^{\ensuremath{'}}$ models. We find that one can extract reliably four combinations of generation-independent quark and lepton couplings in our analysis. For a ${Z}^{\ensuremath{'}}$ mass of 1.5 TeV, one can determine coupling information very well assuming $100\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity, and a precise measurement becomes possible with $1{\mathrm{ab}}^{\ensuremath{-}1}$ at the super-LHC (SLHC). For a 3 TeV mass, a reasonable determination requires the SLHC.

Tagging sneutrino resonances at a linear collider with associated photons

Sneutrino resonances at a high-energy linear ${e}^{+}{e}^{\ensuremath{-}}$ collider may be one of the clearest signals of supersymmetry without $R$ parity, especially when the $R$-parity-violating coupling is too small to produce observable excesses in four-fermion processes. However, there is no guarantee that the sneutrino pole will lie anywhere near the machine energy. We show that associated photon production induces the necessary energy spread, and that the resonance then leaves a clear imprint in the photon spectrum. It follows that tagging of a hard monoenergetic photon for a variety of possible final states provides a realistic method of separating sneutrino resonance signals from the standard model backgrounds.

Constraints on the parity-violating couplings of a new gauge boson

High-energy particle physics experiments allow for the possible existence of a new light, very weakly coupled, neutral gauge boson (the U boson). This one permits for light (spin-12 or spin-0) particles to be acceptable Dark Matter candidates, by inducing sufficient (stronger than weak) annihilation cross sections into e+e−. They could be responsible for the bright 511 keV γ ray line observed by INTEGRAL from the galactic bulge. Such a new interaction may have important consequences, especially at lower energies. Parity-violation atomic-physics experiments provide strong constraints on such a U boson, if its couplings to quarks and electrons violate parity. With the constraints coming from an unobserved axionlike behaviour of this particle, they favor a pure vector coupling of the U boson to quarks and leptons, unless the corresponding symmetry is broken sufficiently above the electroweak scale.

THE ANAPOLE MOMENT OF DIRAC NEUTRINOS IN LEFT–RIGHT SYMMETRIC MODEL AND IN MINIMAL SUPERSYMMETRIC MODEL

The static parity-violating coupling of Dirac neutrino to an external electromagnetic field is calculated in the SU (2) L × SU (2) R × U (1) left–right model and in the N=1 broken supergravity model (MSSM).

Light quark fragmentation in polarized Z0 decays at SLD

We report results on two physics topics from the SLD experiment at the SLAC Linear Collider, using our full sample of 550,000 events of the type e + e − → Z 0 → q q . The electron beam was polarized, enabling the quark and antiquark hemispheres to be tagged in each event. One physics topic is the first study of rapidities signed such that positive rapidity is along the quark rather than antiquark direction. Distributions of ordered differences in signed rapidity between pairs of particles are analyzed, providing the first direct observation of baryon number ordering along the q q axis. The other topic is the first direct measurement of A s , the parity-violating coupling of the Z 0 to strange quarks, by measuring the left-right forward-backward production asymmetry in polar angle of the tagged s quark. We obtain A s = 0.895 ± 0.066( stat.) ± 0.062( syst.), which is consistent with the Standard Model and is currently the most precise measurement of this quantity.

First direct measurement of the parity-violating coupling of the Z0 to the s quark

We present the first direct measurement of A(s), the parity-violating coupling of the Z0 boson to the strange quark, using approximately 550 000 e(+)e(-)-->Z0-->hadrons events recorded by the SLC Large Detector with a polarized e(-) beam. We tagged Z0-->s&smacr; events by the absence of B or D hadrons and the presence in each hemisphere of a high momentum K+/- or K(0)(s). Fitting the polar angle distributions of the strangeness-signed thrust axis gave A(s) = 0.895+/-0.066(stat)+/-0.062(syst). The analyzing power and uu+d&dmacr; background were constrained using the data, greatly reducing any model dependence.

Identified hadron production and light quark fragmentation in Z0 decays

We have measured the differential cross sections for the production of π +, K +, K 0, K ∗0 , φ, p, Λ and their corresponding antiparticles in separate samples of flavor-tagge Z 0 → light-flavor ( u u − , d d − , or s s − ), Z 0 → c c − and Z 0 → b b − events. Clear flavor dependences are observed, and the results are compared with the predictions of three fragmentation models. We have also performed a direct measurement of A s , the parity-violating coupling of the Z 0 to strange quarks, by measuring the left-right-forward-backward production asymmetry in polar angle of the tagged s quark. Our preliminary result is A s = 0.82 ± 0.10( stat.) ± 0.07( syst.).

B→Xsli+lj−decays withR-parity violation

We consider $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}{l}_{i}^{+}{l}_{j}^{\ensuremath{-}}$ decays in the minimal supersymmetric standard model with explicit $R$-parity violation. From the present upper limits on the branching ratios for these processes, we obtain the constraints on the product combinations of the $R$-parity-violating couplings which are in many cases more severe than the previous ones. Taking into account the invariant dilepton mass spectrum and the forward-backward asymmetry of the emitted leptons, we show that the spectra and asymmetries obtained from $R$-parity-violating interactions are different from the SM ones. Therefore, they may be used in the future to disentangle $R$-parity-violating effects from the SM in these processes. We also show that it is possible to discriminate two types of $R$-parity-violating effects from each other. The general expectation of the enhancement of the forward-backward asymmetry of the emitted leptons in the minimal supersymmetric standard model with $R$ parity may be corrupted by $R$-parity violation.