FASER, the ForwArd Search ExpeRiment, is a currently
operating experiment at the Large Hadron Collider (LHC) that can
detect light long-lived particles produced in the forward region of
the LHC interacting point. In this talk, we show the prospect of
detecting light CP-even and CP-odd scalars at FASER and FASER 2.
Considering a model-independent framework describing the most general
interactions between a CP-even or CP-odd scalar and SM particles using
the notation of coupling modifiers in the effective Lagrangian, we
develop the general formalism for the scalar production and decay. We
then analyze the FASER and FASER 2 reaches of light scalars in the
large tan beta region of the Type-I two Higgs doublet model as a case
study, in which light scalars with relatively long lifetime could be
accommodated. Both FASER and FASER 2 can probe a large part of the
parameter space in the large tan beta region up to 10^7, extending
beyond the constraints of the other existing experiments.