Searcharxiv⌕ Search

arXiv subjects

Harleen Dahiya

Publications and source records attributed to Harleen Dahiya.

At least 127 records · Page 7Linked to original sources
arXiv2010

Spin 1/2^+, spin 3/2^+ and transition magnetic moments of low lying and charmed baryons

Magnetic moments of the low lying and charmed spin 1/2^+ and spin 3/2^+ baryons have been calculated in the SU(4) chiral constituent quark model (\chiCQM) by including the contribution from c \bar c fluctuations. Explicit calculations have been carried out for the contribution coming from the valence quarks, "quark sea" polarizations and their orbital angular momentum. The implications of such a model have also been studied for magnetic moments of the low lying spin 3/2^+ \to 1/2^+ and 1/2^+ \to 1/2^+ transitions as well as the transitions involving charmed baryons. We are able to achieve an excellent agreement with data for the case of low lying spin 1/2^+ baryons and spin 3/2^+ baryons. For the spin 1/2^+ and spin 3/2^+ charmed baryon magnetic moments, our results are consistent with the predictions of the QCD sum rules, Light Cone sum rules and Spectral sum rules. For the cases where "light" quarks dominate in the valence structure, the sea and orbital contributions are found to be fairly significant however, they cancel in the right direction to give the correct magnitude of the total magnetic moment. On the other hand, when there is an excess of "heavy" quarks, the contribution of the "quark sea" is almost negligible. The effects of configuration mixing and quark masses have also been investigated.

hep-ph↗
arXiv2010

Nucleon shape and electromagnetic form factors in the chiral constituent quark model

The electromagnetic form factors are the most fundamental quantities to describe the internal structure of the nucleon and the shape of a spatially extended particle is determined by its intrinsic quadrupole moment which can be related to the charge radii. We have calculated the electromagnetic form factors, nucleon charge radii and the intrinsic quadrupole moment of the nucleon in the framework of chiral constituent quark model. The results obtained are comparable to the latest experimental studies and also show improvement over some theoretical interpretations.

hep-ph↗
arXiv2009

Magnetic moments of spin {1/2}^+ and spin {3/2}^+ charmed baryons

The magnetic moments of spin ${1/2}{^+}$ and spin ${3/2}{^+}$ charmed baryons have been calculated in chiral constituent quark model ($χ$CQM). The effects of configuration mixing and quark masses have also been investigated. The results are not only in good agreement with existing experimental data but also show improvement over other phenomenological models.

hep-ph↗
arXiv2009

Weak vector and axial-vector form factors in the chiral constituent quark model with configuration mixing

The effects of SU(3) symmetry breaking and configuration mixing have been investigated for the weak vector and axial-vector form factors in the chiral constituent quark model (χCQM) for the strangeness changing as well as strangeness conserving semi-leptonic octet baryon decays in the nonperturbative regime. The results are in good agreement with existing experimental data and also show improvement over other phenomenological models.

hep-ph↗
arXiv2008

Semi-leptonic Octet Baryon Weak Axial-Vector Form Factors in the Chiral Constitutent Quark Model

The weak vector and axial-vector form factors have been investigated for the semi-leptonic octet baryon decays in the chiral constituent quark model with configuration mixing (\chiCQM_{config}). The effects of SU(3) symmetry breaking and configuration mixing have also been investigated and the results are not only in good agreement with existing experimental data but also show improvement over other phenomenological models.

hep-ph↗
arXiv2008

Spin and Flavor Strange Quark Content of the Nucleon

Several spin and flavor dependent parameters characterizing the strangeness content of the nucleon have been calculated in the chiral constituent quark model with configuration mixing (\chiCQM_{config}) which is known to provide a satisfactory explanation of the ``proton spin crisis'' and related issues. In particular, we have calculated the strange spin polarization Δs, the strangeness contribution to the weak axial vector couplings Δ_8 etc., strangeness contribution to the magnetic moments μ(p)^s etc., the strange quark flavor fraction f_s, the strangeness dependent quark flavor ratios \frac{2 \bar s}{u+d} and \frac{2 \bar s}{\bar u+ \bar d} etc.. Our results are consistent with the recent experimental observations.

hep-ph↗
arXiv2008

Chiral Odd Generalized Parton Distributions in Impact Parameter Space

We investigate the chiral odd generalized parton distributions (GPDs) for the quantum fluctuations of an electron in QED. The light-front wave function (LFWF) of this system gives a template for the quark spin-one diquark structure of the valence LFWF of the proton. We express the GPDs in terms of overlaps of LFWFs and obtain their representation in impact parameter space when the momentum transfer is purely transverse. We show the spin-orbit correlation effect of the two-particle LFWF as well as the correlation between the constituent spin and the transverse spin of the target.

hep-ph↗
arXiv2007

Strangeness Content of the Nucleon in the \chiCQM_{config}

Several parameters characterizing the strangeness content of the nucleon have been calculated in the chiral constituent quark model with configuration mixing (\chiCQM_{config}) which is known to provide a satisfactory explanation of the ``proton spin problem'' and related issues. In particular, we have calculated the strange spin polarization Δs, the strangeness contribution to the weak axial vector couplings Δ_8 etc., strangeness contribution to the magnetic moments μ(p)^s etc., the strange quark flavor fraction f_s, the strangeness dependent quark ratios \frac{2 \bar s}{u+d} and \frac{2 \bar s}{\bar u+\bar d} etc.. Our results show in general excellent agreement with the recent experimental observations.

hep-ph↗
arXiv2007

$x-$dependence of the quark distribution functions in the $χ$CQM$_{\rm config}$

Chiral constituent quark model with configuration mixing (\chiCQM_{\rm config}) is known to provide a satisfactory explanation of the ``proton spin problem'' and related issues. In order to enlarge the scope of \chiCQM_{\rm config}, we have attempted to phenomenologically incorporate x-dependence in the quark distribution functions. In particular, apart from calculating valence and sea quark distributions q_{\rm val}(x) and \bar q(x), we have carried out a detailed analysis to estimate the sea quark asymmetries \bar d(x)-\bar u(x), \bar d(x)/\bar u(x) and \frac{\bar d(x)-\bar u(x)}{u(x)-d(x)} as well as spin independent structure functions F_2^p(x)-F_2^n(x) and $F_2^n(x)/F_2^p(x)$ as functions of $x$. We are able to achieve a satisfactory fit for all the above mentioned quantities simultaneously. The inclusion of effects due to configuration mixing have also been examined in the case F_2^p(x)-F_2^n(x) and F_2^n(x)/F_2^p(x) where the valence quark distributions dominate and it is found that it leads to considerable improvement in the results. Further, the valence quark structure has also be tested by extrapolating the predictions of our model in the limit x \to 1 where data is not available.

hep-ph↗
arXiv2007

Strangeness in the Nucleon

There are several different experimental indications, such as the strangeness contribution to the magnetic moment of the proton, sigma_{πN} term, strange spin polarization, ratio of strange and non strange quark flavor distributions which suggest that the nucleon contains a hidden strangeness component which is contradictory to the naive constituent quark model. Chiral constituent quark model with configuration mixing (\chiCQM_{\rm config}) is known to provide a satisfactory explanation of the ``proton spin problem'' and related issues. In the present work, we have extended the model to carry out the calculations for the parameters pertaining to the strange quark content of the nucleon, for example, the strange spin polarization Δs, strange components of the weak axial vector form factors ΔΣand Δ_8 as well as F and D, strangeness magnetic moment of the proton μ_p^s, the strange quark content in the nucleon f_s coming from the σ_{πN} term, the ratios between strange and non-strange quarks \frac{2 s}{u+d} and \frac{2 s}{\bar u+ \bar d}, contribution of strangeness to angular momentum sum rule etc.. Our result demonstrates the broad consistency with the experimental observations as well as other theoretical considerations.

hep-ph↗
arXiv2007

Implications of η' Coupling in the Chiral Constituent Quark Model

Using the latest data pertaining to \bar u-\bar d asymmetry and the spin polarization functions, detailed implications of the possible values of the coupling strength of the singlet Goldstone boson η' have been investigated in the \chiCQM with configuration mixing. Using Δu, Δ_3, \bar u-\bar d and \bar u/\bar d, the possible ranges of the coupling parameters a, α^2 a, β^2 a and ζ^2 a, representing respectively the probabilities of fluctuations to pions, K, ηand η^{'}, are found. To further constrain the coupling strength of η', detailed fits have been obtained for spin polarization functions, quark distribution functions and baryon octet magnetic moments. The fits clearly establish that a small non-zero value of the coupling of η' is preferred over the higher values of $η'$ as well as when ζ=0, the latter implying the absence of η' from the dynamics of \chiCQM. Our best fit achieves an overall excellent fit to the data, in particular for Δu, Δd, Δ_8 as well as the magnetic moments μ_{n}, μ_{Σ^-}, μ_{Σ^+} and μ_{Ξ^-}. The implications of η' on the gluon polarization have also been investigated.

hep-ph↗
arXiv2006

Chiral constituent quark model and the coupling strength of eta'

Using the latest data pertaining to \bar u-\bar d asymmetry and the spin polarization functions, detailed implications of the possible values of the coupling strength of the singlet Goldstone boson η' have been investigated in the \chiCQM with configuration mixing. Using Δu, Δ_3, \bar u-\bar d and \bar u/\bar d, the possible ranges of the coupling parameters a, α^ 2, β^ 2 and ζ^ 2, representing respectively the probabilities of fluctuations to pions, K, ηand η^{'}, are shown to be 0.10 \lesssim a \lesssim 0.14, 0.2\lesssim α\lesssim 0.5, 0.2\lesssim β\lesssim 0.7 and 0.10 lesssim |ζ| \lesssim 0.70. To constrain the coupling strength of η', detailed fits have been obtained for spin polarization functions, quark distribution functions and baryon octet magnetic moments corresponding to the following sets of parameters: a=0.1, α=0.4, β=0.7, |ζ|=0.65 (Case I); a=0.1, α=0.4, β=0.6, |ζ|=0.70 (Case II); a=0.14, α=0.4, β=0.2, ζ=0 (Case III) and a=0.13, α=β=0.45, |ζ|=0.10 (Case IV). Case I represents the calculations where a is fixed to be 0.1, in accordance with earlier calculations, whereas other parameters are treated free and the Case IV represents our best fit. The fits clearly establish that a small non-zero value of the coupling of η' is preferred over the higher values of η' as well as when ζ=0, the latter implying the absence of η' from the dynamics of \chiCQM. Our best fit achieves an overall excellent fit to the data, in particular the fit for Δu, Δd, Δ_8 as well as the magnetic moments μ_{n}, μ_{Σ^-}, μ_{Σ^+} and μ_{Ξ^-} is almost perfect, the μ_{Ξ^-} being a difficult case for most of the similar calculations.

hep-ph↗
arXiv2004

Singlet GB contributions in the chiral constituent quark model

The implications of the latest data pertaining to \bar u-\bar d asymmetry and the spin polarization functions on the contributions of singlet Goldstone boson η' within \chiCQM with configuration mixing for explaining the ``proton spin problem'' have been investigated. It is found that the present data favors smaller values of the coupling of singlet Goldstone Boson η' as compared to the corresponding contributions from π, K and ηGoldstone bosons. It seems that a small non-zero value of the coupling of η' (ζ\neq 0) is preferred over ζ=0 phenomenologically.

hep-ph↗
arXiv2004

Chiral quark model and the nucleon spin

Using \chiQM with configuration mixing, the contribution of the gluon polarization to the flavor singlet component of the total spin has been calculated phenomenologically through the relation ΔΣ(Q^2)=ΔΣ-\frac{3α_s(Q^2)}{2π}Δg(Q^2) as defined in the Adler-Bardeen scheme, where ΔΣon the right hand side is Q^2 independent. For evaluation the contribution of gluon polarization Δg'(=\frac{3α_s(Q^2)}{2π}Δg(Q^2)), ΔΣis found in the \chiQM by fixing the latest E866 data pertaining to \bar u-\bar d asymmetry and the spin polarization functions whereas ΔΣ(Q^2) is taken to be 0.30\pm0.06 and α_s= 0.287\pm0.020, both at Q^2=5{\rm GeV}^2. The contribution of gluon polarization Δg' comes out to be 0.33 which leads to an almost perfect fit for spin distribution functions in the \chiQM. When its implications for magnetic moments are investigated, we find perfect fit for many of the magnetic moments. If an attempt is made to explain the angular momentum sum rule for proton by using the above value of Δg', one finds the contribution of gluon angular momentum to be as important as that of the q \bar q pairs.

hep-ph↗
arXiv2003

Octet and Decuplet Baryon Magnetic Moments in the Chiral Quark Model

Octet and decuplet baryon magnetic moments have been formulated within the \chiQM with configuration mixing incorporating the sea quark polarizations and their orbital angular momentum through the generalization of the Cheng-Li mechanism. When the parameters of \chiQM without configuration mixing are fixed by incorporating the latest data pertaining to $\bar u-\bar d$ asymmetry (E866) and the spin polarization functions, in the case of octet magnetic moments the results not only show improvement over the nonrelativistic quark model results but also give a non zero value for the right hand side of Coleman-Glashow sum rule, usually zero in most of the models. When effects of configuration mixing and ``mass adjustments'' due to confinement are included, in the case of p, Σ^+, Ξ^o, the ΣΛtransition magnetic moment and the violation of Coleman Glashow sum rule an almost perfect agreement with data is obtained. In the case of decuplet magnetic moments, we obtain a good overlap for Δ^{++}, Ω^- and the transition magnetic moment $ΔN$ for which data are available. In case, we incorporate in our analysis the gluon polarization Δg, found phenomenologically through the relation ΔΣ(Q^2)=ΔΣ-\frac{3α_s(Q^2)}{2π}Δg(Q^2), we not only obtain improvement in the quark spin distribution functions and magnetic moments but also the value of Δg comes out to be in good agreement with certain recent measurements as well as theoretical estimates.

hep-ph↗
arXiv2003

SU(4) Chiral Quark Model with Configuration Mixing

Chiral quark model with configuration mixing and broken SU(3)\times U(1) symmetry has been extended to include the contribution from c\bar c fluctuations by considering broken SU(4) instead of SU(3). The implications of such a model have been studied for quark flavor and spin distribution functions corresponding to E866 and the NMC data. The predicted parameters regarding the charm spin distribution functions, for example, Δc, \frac{Δc}{ΔΣ}, \frac{Δc}{c} as well as the charm quark distribution functions, for example, \bar c, \frac{2\bar c}{(\bar u+\bar d)}, \frac{2 \bar c}{(u+d)} and \frac{(c+ \bar c)}{\sum (q+\bar q)} are in agreement with other similar calculations. Specifically, we find Δc=-0.009, \frac{Δc}{ΔΣ}=-0.02, \bar c=0.03 and \frac{(c+ \bar c)}{\sum (q+\bar q)}=0.02 for the \chiQM parameters a=0.1, α=0.4, β=0.7, ζ_{E866}=-1-2 β, ζ_{NMC}=-2-2 βand γ=0.3, the latter appears due to the extension of SU(3) to SU(4).

hep-ph↗
arXiv2002

Octet magnetic moments and the Coleman-Glashow sum rule violation in the chiral quark model

Baryon octet magnetic moments when calculated within the chiral quark model, incorporating the orbital angular momentum as well as the quark sea contribution through the Cheng-Li mechanism, not only show improvement over the non relativistic quark model results but also gives a non zero value for the right hand side of Coleman-Glashow sum rule. When effects due to spin-spin forces between constituent quarks as well as `mass adjustments' due to confinement are added, it leads to an excellent fit for the case of p, Σ^+, Ξ^o and violation of Coleman-Glashow sum rule, whereas in almost all the other cases the results are within 5% of the data.

hep-ph↗
arXiv2002

Octet magnetic moments and the violation of CGSR in $χ$QM with configuration mixing

Octet baryon magnetic moments are calculated within \chiQM, respecting color spin spin forces (Szczepaniak et al., PRL 87, 072001(2001)), incorporating the orbital angular momentum as well as the quark sea contribution through the Cheng and Li mechanism (PRL 80, 2789(1998)). Using configuration mixing generated by color spin spin forces as well as the concept of ``effective'' quark mass to include the effects of confinement, we are able to get an excellent fit to the octet magnetic moments as well as the violation of Coleman Glashow Sum Rule (CGSR) without any further input except for the ones already used in \chiQM as well as in NRQM. Specifically, in the case of p, Σ^+, Ξ^o, and violation of CGSR we get a perfect fit whereas in almost all the other cases the results are within 5% of the data.

hep-ph↗