Abstract
Motivated by the ongoing searches for new physics at the LHC, we explore the low energy consequences of a D-brane inspired $ SU(4)_C\times SU(2)_L \times SU(2)_R$ (4-2-2) model. The Higgs sector consists of an $SU(4)$ adjoint, a pair $H+\bar H$ in $(4,1,2)+(\bar 4,1,2)$, and a bidoublet field in $h(1,2,2)$. With the $SU(4)$ adjoint the symmetry breaks to a left-right symmetric $SU(3)_C\times U(1)_{B-L} \times SU(2)_L \times SU(2)_R$ model. A missing partner mechanism protects the $SU(2)_R$ Higgs doublets in $H,\bar H$, which subsequently break the symmetry to the Standard Model at a few TeV scale. An inverse seesaw mechanism generates masses for the observed neutrinos and also yields a sterile neutrino which can play the r\^ole of dark matter if its mass lies in the keV range. Other phenomenological implications including proton decay are briefly discussed.
Highlights
Broken left-right symmetry and the idea of quark-lepton unification are nicely encapsulated in the SUð4ÞC × SUð2ÞL × SUð2ÞR (4-2-2) gauge symmetry proposed by Pati and Salam (PS) [1]
We have analyzed a class of 4-2-2 models within the framework of intersecting D-branes
The low energy spectrum contains additional particles that normally do not appear in the usual field theory based
Summary
Broken left-right symmetry and the idea of quark-lepton unification are nicely encapsulated in the SUð4ÞC × SUð2ÞL × SUð2ÞR (4-2-2) gauge symmetry proposed by Pati and Salam (PS) [1]. Quarks and leptons, its symmetry structure consists of a product of non-Abelian factors and, as such, does not necessarily imply unification of the gauge couplings Given this fact, from the above string theory realizations, the intersecting D-brane set up appears to be the most natural scenario. Since the magnitude of these VEVs determines the breaking scale, the anomalous Uð1Þ symmetries are expected to break at the compactification scale too The solution of these issues is related to the specific string construction one considers, and it is of particular importance in the subsequent analysis since it is decisive in shaping the effective field theory model and its low energy predictions. In particular, that the triplet pair D−3 þ Dþ3 found in the decomposition of the sextets has the quantum numbers of leptoquarks, since they simultaneously carry both baryon and lepton numbers under the definitions (3), (4)
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