  We use a $\mathcal{O}(\Lambda_\text{QCD}/m_c)$ heavy quark effective theory
scheme, where only $\mathcal{O}(\Lambda_\text{QCD}/m_b)$ and perturbative QCD
short distance corrections are neglected, to study the matrix elements of the
scalar, pseudoscalar, vector, axial-vector and tensor currents between the
$\Lambda_b$ ground state and the odd parity charm $\Lambda_c(2595)^+$ and
$\Lambda_c(2625)^+$ resonances. We show that in the near-zero recoil regime,
the scheme describes reasonably well, taking into account uncertainties, the
results for the 24 form-factors obtained in lattice QCD (LQCD) just in terms of
only 4 Isgur-Wise (IW) functions. We also find some support for the possibility
that the $\Lambda_c(2595)^+$ and $\Lambda_c(2625)^+$ resonances might form a
heavy-quark spin symmetry (HQSS) doublet. However, we argue that the available
LQCD description of these two resonances is not accurate enough to disentangle
the possible effects of the $\Sigma_c \pi$ and $\Sigma_c^*\pi$ thresholds,
located only a few MeV above their position, and that it cannot be ruled out
that these states are not HQSS partners. Finally, we study the ratio
$\frac{d\Gamma[\Lambda_b\to \Lambda_{c,1/2^-}^* \ell
\bar\nu_\ell]/dq^2}{d\Gamma[\Lambda_b\to \Lambda_{c,3/2^-}^*\ell
\bar\nu_\ell]/dq^2}$ of the Standard Model differential semileptonic decay
widths, with $q^\mu$ the momentum transferred between the initial and final
hadrons. We provide a natural explanation for the existence of large
deviations, near the zero recoil, of this ratio from 1/2 (value predicted in
the infinite heavy quark mass limit, assuming that the $\Lambda_{c,1/2^-}^*$
and $\Lambda_{c,3/2^-}^*$ are the two members of a HQSS doublet) based on
S-wave contributions to the $\Lambda_b\to \Lambda_{c,1/2^-}^*$ decay amplitude
driven by a sub-leading IW function.

High Energy Physics - Phenomenology