Astrophysical Constraints on Singlet Scalars at LHC
  We consider the viability of new heavy gauge singlet scalar particles at
colliders such as the LHC. Our original motivation for this study came from the
possibility of a new heavy particle of mass ~ TeV decaying significantly into
two photons at colliders, such as LHC, but our analysis applies more broadly.
We show that there are significant constraints from astrophysics and cosmology
on the simplest UV complete models that incorporate such new particles and its
associated collider signal. The simplest and most obvious UV complete model
that incorporates such signals is that it arises from a new singlet scalar (or
pseudo-scalar) coupled to a new electrically charged and colored heavy fermion.
Here we show that these new fermions (and anti-fermions) would be produced in
the early universe, then form new color singlet heavy mesons with light quarks,
obtain a non-negligible freeze-out abundance, and remain in kinetic equilibrium
until decoupling. These heavy mesons possess interesting phenomenology,
dependent on their charge, including forming new bound states with electrons
and protons. We show that a significant number of these heavy states would
survive for the age of the universe and an appreciable number would eventually
be contained within the earth and solar system. We show that this leads to
detectable consequences, including the production of highly energetic events
from annihilations on earth, new spectral lines, and, spectacularly, the
destabilization of stars. The lack of detection of these consequences rules out
such simple UV completions, putting pressure on the viability of such new
particles at LHC. To incorporate such a scalar would require either much more
complicated UV completions or even further new physics that provides a decay
channel for the associated fermion.
