LHC phenomenology and cosmology of string-inspired intersecting D-brane models

Abstract

We discuss the phenomenology and cosmology of a Standardlike Model inspired by string theory, in which the gauge fields are localized on D-branes wrapping certain compact cycles on an underlying geometry, whose intersection can give rise to chiral fermions. The energy scale associated with string physics is assumed to be near the Planck mass. To develop our program in the simplest way, we work within the construct of a minimal model with gauge-extended sector $U(3{)}_{B}\ifmmode\times\else\texttimes\fi{}Sp(1{)}_{L}\ifmmode\times\else\texttimes\fi{}U(1{)}_{{I}_{R}}\ifmmode\times\else\texttimes\fi{}U(1{)}_{L}$. The resulting $U(1)$ content gauges the baryon number $B$, the lepton number $L$, and a third additional Abelian charge ${I}_{R}$ which acts as the third isospin component of an $SU(2{)}_{R}$. All mixing angles and gauge couplings are fixed by rotation of the $U(1)$ gauge fields to a basis diagonal in hypercharge $Y$ and in an anomaly-free linear combination of ${I}_{R}$ and $B\ensuremath{-}L$. The anomalous ${Z}^{\ensuremath{'}}$ gauge boson obtains a string scale St\"uckelberg mass via a 4D version of the Green-Schwarz mechanism. To keep the realization of the Higgs mechanism minimal, we add an extra $SU(2)$ singlet complex scalar, which acquires a VEV and gives a TeV-scale mass to the nonanomalous gauge boson ${Z}^{\ensuremath{'}\ensuremath{'}}$. The model is fully predictive and can be confronted with dijet and dilepton data from LHC8 and, eventually, LHC14. We show that ${M}_{{Z}^{\ensuremath{'}\ensuremath{'}}}\ensuremath{\approx}3--4\text{ }\text{ }\mathrm{TeV}$ saturates current limits from the CMS and ATLAS Collaborations. We also show that for ${M}_{{Z}^{\ensuremath{'}\ensuremath{'}}}\ensuremath{\lesssim}5\text{ }\text{ }\mathrm{TeV}$, LHC14 will reach discovery sensitivity $\ensuremath{\gtrsim}5\ensuremath{\sigma}$. After that, we demonstrate in all generality that ${Z}^{\ensuremath{'}\ensuremath{'}}$ milliweak interactions could play an important role in observational cosmology. Finally, we examine some phenomenological aspects of the supersymmetric extension of the D-brane construct.