Searcharxiv⌕ Search

arXiv subjects

Manmohan Gupta

Publications and source records attributed to Manmohan Gupta.

At least 55 records · Page 3Linked to original sources

$x-$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↗

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↗

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↗

Implications of unitarity and precision measurements on CKM matrix elements

Unitarity along with precision measurements of sin2β, V_{us} and V_{cb} allows one to find a lower bound V_{ub}\geq 0.0035 which, on using the recently measured angle αof the unitarity triangle, translates to V_{ub}= 0.0035\pm 0.0002. This precise value, stable for a good deal of changes in α, along with CP violating phase δfound from unitarity allows the construction of a `precise' CKM matrix. The above unitarity based value of V_{ub} is in agreement with the latest exclusive value used as input by UTfit, CKMfitter, HFAG, however underlines the so called `tension' faced by the latest inclusive V_{ub}=0.00449 \pm 0.00033. Further, using this inclusive value of V_{ub} along with the latest sin2β, one finds δ=23 ^{\rm o}- 39 ^{\rm o}, again in conflict with δmeasured in B-decays. The calculated ranges of the elements of the CKM matrix are in excellent agreement with those obtained recently by UTfit, CKMfitter and HFAG. Also, the ratio \frac{V_{ts}}{V_{td}} is in agreement with its latest measured value, whereas there is some disagreement between the `measured' and the calculated V_{td} values.

hep-ph↗

Constructing the CKM and PMNS matrices from mixing data

The CKM and PMNS matrices have been constructed based on the latest measurements, largely free from theoretical inputs as well as likely NP effects in the case of the former. To facilitate the construction of the CKM matrix in the PDG representation as well as in view of the comparatively large error in the measured value of the CP violating phase δ, the possibility of its construction from the tree level measured CKM elements has also been explored using the unitarity triangle. In view of the persistent difference between the |V_{ub}| exclusive and inclusive values, we have carried out separate analyses corresponding to these. The PMNS matrix has been constructed by incorporating the constraints due to solar and atmospheric neutrinos as well as by giving full variation to the Dirac-like CP violating phase δand considering different values of s_{13} having implications for different models of lepton mass matrices. Taking clue from quark mixing phenomenology, an analogous analysis of the leptonic unitarity triangle allows an estimate of the likely presence of CP violation in the leptonic sector.

hep-ph↗

Implications of Fritzsch-like lepton mass matrices

Using seesaw mechanism and Fritzsch-like texture 6 zero and 5 zero lepton Dirac mass matrices, detailed predictions for cases pertaining to normal/inverted hierarchy as well as degenerate scenario of neutrino masses have been carried out. All the cases considered here pertaining to inverted hierarchy and degenerate scenario of neutrino masses are ruled out by the existing data. For the normal hierarchy cases, the lower limit of m_{ν1} and of s_{13} as well as the range of Dirac-like CP violating phase δwould have implications for the texture 6 zero and texture 5 zero cases considered here.

hep-ph↗

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↗

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↗

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↗

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↗

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↗

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↗

Implications of texture 4 zero lepton mass matrices for U_{e3}

Lepton mass matrices similar to texture 4 zero quark mass matrices, known to be quite successful in explaining the CKM phenomenology, have been considered for finding the mixing matrix element U_{e3} (\equiv s_{13}) respecting the CHOOZ constraint, with s_{12} and Δm_{12}^2 constrained by SNP and s_{23} and Δm_{23}^2 constrained by ANP. Taking charged lepton mass matrix M_l to be diagonal, we find that the ranges of s_{13} corresponding to different SNP solutions very well include the corresponding values of s_{13} found by Akhmedov et al. by considering neutrino mass matrix M_ν with no texture zeros. Considering M_l and M_ν both to be real and non-diagonal, s_{13} ranges for the four SNP solutions come out to be: \sim 0-0.19 (LMA), 0.038-0.093 (SMA), 0.042-0.095 (LOW), 0.038-0.096 (VO) which remain of the same order when M_l and M_ν are considered to be complex and non-diagonal.

hep-ph↗

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↗

Probing CKM parameters through unitarity, ε_K and Δm_{B_{d,s}}

The unitarity based analysis carried out in hep-ph/0106161, involving the evaluation of Jarlskog's rephasing invariant parameter J and the angles of the unitarity triangle is extended to include the effects of K^0-\bar K^0 and B^0-\bar B^0 mixings. The present analysis attempts to evaluate CP violating phase δ, V_{td} and the angles of the unitarity triangle by invoking the constraints imposed by unitarity, K^0 -\bar K^0 and B^0 -\bar B^0 mixings separately as well as collectively, using the "full scanning" of input parameters. Interestingly, our results indicate that the lower limit of δis mostly determined by unitarity, while the upper limit is governed by constraints from Δm_{B_d}. Our analysis yields sin2β=0.50-0.88, which is in agreement with the BABAR results, however has marginal overlap only with the lower limit of recent BELLE results.

hep-ph↗

Exploring the construction of "Reference" triangle through unitarity

Motivated by the possibility of the low value of sin2βin the measurements of BABAR and BELLE collaborations, we have explored the possibilty of construction of reference unitarity triangle using the unitarity of the CKM matrix, the existence of nonzero CP violating phase δand the experimental values of the well known CKM elements, without involving any inputs from the processes which might include the new physics effects. The angles of the reference triangle are evaluated by finding δthrough the Jarlskog's rephasing invariant parameter J. The present data and the unitarity of the CKM matrix give δ=50^o \pm 20^o, which translates to 130^o \pm 20^o in the second quadrant. The corresponding range for sin2βis 0.21 to 0.88. This range is broadly in agreement with the recently updated BABAR and BELLE results. However, a value of \sin2 \leq 0.2, advocated by Silva and Wolfenstein as a benchmark for new physics, would suggest a violation in the three generation unitarity and would hint towards the existence of a fourth generation. Further, the future refinements in the CKM elements will push the lower limit on sin2βstill higher.

hep-ph↗

Three flavor neutrino oscillations, LSND, SNP and ANP

The recently reanalysed LSND data is investigated in the context of three flavor oscillations, with an emphasis on mass hierarchies and $s_{13}$. The resultant mass hierarchies and oscillation angles are tested with regard to "key" features of solar neutrinos and atmospheric neutrinos, e.g., "average" survival probability in the case of solar neutrinos, and zenith angle dependence and up-down asymmetry in the case of high energy atmospheric neutrinos. We find there are three distinct mass hierarchies, e.g., $Δm << ΔM, Δm < ΔM$ and $Δm \simeq ΔM$. In the first and second case, the calculated range of $s_{13}$ is in agreement with the "LMA" solution of Akhmedov {\it et al.}, the lower limit on $s_{13}$ in these cases is also in agreement with the recent analysis of Garcia {\it et al.} based on the constraints of SNP, ANP and CHOOZ, therefore, strongly supporting the neutrino oscillations observed at LSND. Further, the solutions of $s_{13}$ found in the third case correspond to the value of $s_{13}$ found by Akhmedov {\it et al.} in the case of "SMA" and "LOW" solutions. A rough estimate of the possibility of the existence of CP violation in the leptonic sector is also carried out for different possible ranges of $s_{13}$, indicating that the CP asymmetries may be measureable even in the case of LSND.

hep-ph↗

What is inside the nucleon?

We briefly review the structure of nucleon in the context of QCD, Constituent Quark Model and Chiral Quark Model.

hep-ph↗