An estimation of the mass difference of$$B_d^0 - \bar B_d^0 $$ system with heavy quark symmetry formalism is presented. The effective Hamiltonian describing the transition$$\bar hd \leftrightarrow h\bar d$$ (whereh=b forB_d⁰-system) is considered in a manifest left right symmetric (MLRS) model along with contribution from neutral Higgs boson. We use the spin and flavor symmetry for heavy quarks to obtain the transition matrix element 〈B_d⁰|ℋ_eff(x)|$$\bar B_d^0 $$_d⁰〉 in terms of Isgur-Wise function. Assuming thatB_d⁰ and$$\bar B_d^0 $$ states are at rest, we find that Isgur-Wise function turns out to be unity. However using the experimental values of ΔM_K and$$\Delta M_{B_4 } $$ as input, we find thatM_R=835 GeV andM_H⩾2·9 TeV.

SU(3) flavor symmetry allows the decay constantsf_D1 andf_D2 as well asf_B1 andf_B1 to be equal. But due toSU(3) flavor symmetry breaking the ratiosf_B1/f_B2 andf_D1/f_D2 are deviated from unity. We have estimated these ratios in the heavy quark effective theory and obtainedf_B1/f_B2=0.93,f_D1/f_D2=0.94 and the double ratio (f_B1/f_B2)/(f_D1/f_D2)=0.99.

The radiative decays of heavy mesons are considered in heavy quark symmetry formalism. Introducing the interpolating fields for the heavy mesons we obtain the transition matrix element and the corresponding decay widths in the heavy quark symmetry limits. The Isgur-Wise function present in the expression is determined by ISGW quark model. The results obtained agree reasonably well with other estimations.

The decay widths for the radiative decays of heavy baryons are calculated in the heavy quark effective theory. Introducing the interpolating fields for heavy baryons we obtain the transition matrix elements and the corresponding decay widths. Considering theSU(6) flavor-spin wave functions for heavy baryons, the coupling constants are calculated in the nonrelativistic quark model. Since the masses of the heavy baryons are not available, we have taken the predicted bag model masses. We find our results are quite different from that of the heavy quark bag model calculations.

We have analysed the two body non-leptonic charmed-meson decays of heavyB meson based on the factorization assumption. The transition matrix elements and the corresponding decay widths are calculated in the heavy quark and chiral symmetry limit and the Isgur-Wise function present in the expression is determined by the wave function model of Aliet al. The results obtained are quite interesting and agree reasonably well with the experimental data.

We have studied some of the two body nonleptonic decays ofB meson in the context of heavy quark effective theory using factorization hypothesis. Treatinga₁ as a free parameter, we have obtained its value asa₁=0.822±0.045, by correlating the experimental and predicted branching ratio for$$\bar B^0 \to D^ + \pi ^ - $$ process. With this value ofa₁ the branching ratios obtained for other decay channels are in good agreement with the experiment. The decay constant ofD meson is extracted to be 280.82 MeV. Heavy quark spin symmetry has also been tested.

The two body non-leptonic Λ_b decays are analysed in the HQET with factorization approximation and largeN_c limit. In this limit, Λ_b and Λ_c baryons can be treated as the bound states of chiral soliton and heavy meson, and consequently the Isgur-Wise function comes out in a straight forward manner. The results obtained remain well below their previously predicted upper limit.

Based on the factorization approximation, we have estimated the ratio of the branching fractions for the color suppressed nonleptonic decays Λ_b→ΛJ/ψ andB⁰→KJ/ψ. Treating thes-quark as heavy, we have used the HQET to calculate the hadronic matrix elements. The mesonic Isgur-Wise function is calculated in the quark model whereas for the baryonic IW function we have employed the bound state soliton picture. The results obtained agree very well with the recent CDF experimental data.

The weak radiative decay Λ_b→Λγ is studied in the heavy quark effective theory treatings-quark as heavy. This rare decay is induced by the short distance electromagnetic penguins. Including corrections of the order of (1/m_Q), we obtain the transition matrix element and the corresponding decay width. The Isgur-Wise function is evaluated in the largeN_c limit and the branching ratio obtained is 1.48×10⁻⁵.

Using the heavy quark approximation, we have studied the nonleptonic decay mode Λ_b→Λ_ca₁. We have included nonfactorizable contributions as well as factorizable ones in our analysis. The estimated branching ratio for this process is (1.4±0.1)% and the asymmetry parameter α found to be −0.8.