Speaker
Description
We explore a possibility that an inflaton, which drives the cosmological inflation in the early universe, can be detected by the recently approved FASER at the High-Luminosity LHC (HL-LHC). We consider nonminimal quartic inflation scenario in the minimal U(1)$_X$ extension of the Standard Model (SM) with the classical conformal invariance, where the inflaton is identified with the U(1)$_X$ Higgs field ($\phi$). By virtue of the classical conformal invariance and the radiative U(1)$_X$ symmetry breaking via the Coleman-Weinberg mechanism, the inflationary predictions (in particular, the tensor-to-scaler ratio ($r$)), the U(1)$_X$ coupling ($g_X$) and the U(1)$_X$ gauge boson mass ($m_{Z^\prime}$), are all determined by only two free parameters, the inflaton mass ($m_\phi$) and its mixing angle ($\theta$) with the SM Higgs field. FASER can search for the inflaton for the parameter ranges of $0.1 \leq m_\phi[{\rm GeV}] \leq 4$ and $10^{-5} \leq \theta \leq 10^{-3}$. Each point in the ($m_\phi$, $\theta$)-plane searched by FASER has a one-to-one correspondence with inflationary predictions ($r$) and $Z^\prime$ boson search parameters ($g_X$ and $m_{Z^\prime}$) at the HL-LHC. Therefore, the cosmological observation, LHC experiment, and long-lived particle search at FASER are complementary to test our scenario.
Summary
We explore a possibility that an inflaton can be detected by the recently approved FASER at the High-Luminosity LHC.
