Pseudosmooth Tribrid Inflation in $SU(5)$
  A realistic tribrid model of sneutrino inflation is constructed in an
$R$-symmetric $SU(5)$ grand unified theory (GUT). To avoid the monopole
problem, a pseudosmooth inflationary trajectory is generated with the help of
an additional $Z_5$ symmetry which is broken during and after inflation. The
predictions of inflationary parameters are made at the central value of the
scalar spectral index, $n_s =0.968$. The largest possible value of the tensor
to scalar ratio, $r\lesssim 0.0027$, is obtained with sub-Planckian field
values ($\lesssim m_P$). A successful realization of reheating and leptogenesis
is achieved by avoiding the gravitino problem with a reheat temperature as low
as $10^6$ GeV. The predicted range of the gauge symmetry breaking scale, $ 5
\times 10^{16} \lesssim M/\text{GeV} \lesssim 5 \times 10^{17}$, turns out to
be somewhat larger than the typical GUT scale. With additional vector-like
families, a successful gauge coupling unification is achieved by avoiding the
no-go theorem related to $R$-symmetric $SU(5)$ GUT.
