The Veneziano ghost field has been proposed as an alternative source of dark energy whose energy density is consistent with the cosmological observations. In this model, the energy density of QCD ghost field is expressed in terms of QCD degrees of fr
eedom at zero temperature. We extend this model to finite temperature to search the model predictions from late time to early universe. We depict the variations of QCD parameters entering the calculations, dark energy density, equation of state, Hubble and deceleration parameters on temperature from zero to a critical temperature. We compare our results with the observations and theoretical predictions existing at different eras. It is found that this model safely defines the universe from quark condensation up to now and its predictions are not in tension with those of the standard cosmology. The EoS parameter of dark energy is dynamical and evolves from $-1/3$ in the presence of radiation to $-1$ at late time. The finite temperature ghost dark energy predictions on the Hubble parameter well fit to those of $Lambda$CDM and observations at late time.
We comparatively analyze the flavor changing neutral current process of the $Lambda_b rightarrow Lambda ell^+ ell^-$ in the standard model as well as topcolor-assisted technicolor model using the form factors calculated via light cone QCD sum rules i
n full theory. In particular, we calculate the decay width, branching ratio and lepton forward-backward asymmetry related to this decay channel. We compare the results of the topcolor-assisted technicolor model with those of the standard model and debate how the results of the topcolor-assisted technicolor model depart from the standard model predictions. We also compare our results on the differential branching ratio with recent experimental data provided by CDF and LHCb Collaborations.
We investigate the radiative process of the $Lambda_brightarrow Lambda gamma$ in the standard model as well as models with one or two compact universal extra dimensions. Using the form factors entered to the low energy matrix elements, calculated via
light cone QCD in full theory, we calculate the total decay width and branching ratio of this decay channel. We compare the results of the extra dimensional models with those of the standard model on the considered physical quantities and look for the deviations of the results from the standard model predictions at different values of the compactification scale (1/R).
We work out the semileptonic $Lambda_brightarrow Lambda ell^+ ell^-$ transition in standard as well as different supersymmetric models. In particular, considering the parametrization of the matrix elements entered the low energy effective Hamiltonian
in terms of form factors in full QCD, we calculate the amplitude and differential decay rate responsible for this decay channel in supersymmetric models. We then use the form factors calculated via light cone QCD sum rules in full theory to analyze the differential branching ratio and lepton forward-backward asymmetry of this decay channel in different supersymmetric models and compare the obtained results with those of the standard model. We also discuss how the results of different supersymmetric models deviate from the standard model predictions and which SUSY scenarios are favored.
Using newly available form factors obtained from light cone QCD sum rules in full theory, we study the flavor changing neutral current transition of $Sigma_b rar Sigma mu^+ mu^-$ decay in the family non-universal $Z^prime$ model. In particular, we ev
aluate the differential branching ratio, forward-backward asymmetry as well as some related asymmetry parameters and polarizations. We compare the obtained results with the predictions of the standard model and discuss the sensitivity of the observables under consideration to family non-universal $Z^prime$ gauge boson. The order of differential branching ratio shows that this decay mode can be checked at LHC in near future.
We obtain a lower limit on the compactification scale of extra dimension via comparison of the branching ratio in the baryonic $Lambda_brightarrow Lambda mu^+ mu^-$ decay channel recently measured by CDF collaboration and our previous theoretical stu
dy. We also use the newly available form factors calculated via light cone QCD sum rules in full theory to analyze the flavour changing neutral current process of the $Sigma_b rightarrow Sigma ell^+ ell^-$ in universal extra dimension scenario in the presence of a single extra compact dimension. We calculate various physical quantities like branching ratio, forward-backward asymmetry, baryon polarizations and double lepton polarization asymmetries defining the decay channel under consideration. We also compare the obtained predictions with those of the standard model.
Using the responsible form factors calculated via full QCD, we analyze the $Lambda_{b}rightarrow Lambda ell^{+}ell^{-}$ transition in the standard model containing fourth generation quarks (SM4). We discuss effects of the presence of $t$ fourth famil
y quark on related observables like branching ratio, forward-backward asymmetry, baryon polarization as well as double lepton polarization asymmetries. We also compare our results with those obtained in the SM as well as with predictions of the SM4 but using form factors calculated within heavy quark effective theory. The obtained results on branching ratio indicate that the $Lambda_{b}rightarrow Lambda ell^{+}ell^{-}$ transition is more probable in full QCD comparing to the heavy quark effective theory. It is also shown that the results on all considered observables in SM4 deviate considerably from the SM predictions when $m_{t}geq 400 GeV$.
We analyze the semileptonic $Bto K_2^*(1430)l^+l^-$ transition in universal extra dimension model. In particular, we present the sensitivity of related observables such as branching ratio, polarization distribution and forward-backward asymmetry to t
he compactification factor (1/R) of extra dimension. The obtained results from extra dimension model show overall a considerable deviation from the standard model predictions for small values of the compactification factor. This can be considered as an indication for existence of extra dimensions.
Using the related form factors from full QCD which recently are available, we provide a comprehensive analysis of the $Lambda_b rightarrow Lambda ell^+ ell^-$ transition in universal extra dimension model in the presence of a single universal extra d
imension called the Applequist-Cheng-Dobrescu model. In particular, we analyze some related observables like branching ratio, forward-backward asymmetry, double lepton polarization asymmetries and polarization of the $Lambda$ baryon in terms of compactification radius and corresponding form factors. We present the sensitivity of these observables to the compactification parameter, 1/R up to 1/R=1000 GeV. We also compare the results with those obtained using the form factors from heavy quark effective theory as well as the SM predictions.
The loop level flavor changing neutral currents transitions of the $Sigma_{b}to n l^+l^-$ and $Sigma_{c}to p l^+l^-$ are investigated in full QCD and heavy quark effective theory in the light cone QCD sum rules approach. Using the most general form o
f the interpolating current for $Sigma_{Q}$, $Q=b$ or $c$, as members of the recently discovered sextet heavy baryons with spin 1/2 and containing one heavy quark, the transition form factors are calculated using two sets of input parameters entering the nucleon distribution amplitudes, namely, QCD sum rules and lattice QCD inputs. The obtained results are used to estimate the decay rates of the corresponding transitions. Since such type transitions occurred at loop level in the standard model, they can be considered as good candidates to search for the new physics effects beyond the SM.
