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Shyam Balaji

Publications and source records attributed to Shyam Balaji.

39 records · Page 3Linked to original sources
arXiv2020

Unified SU(4) theory for the $R_{D^{(*)}}$ and $R_{K^{(*)}}$ anomalies

We propose a chiral Pati-Salam theory based on the gauge group $SU(4)_C\times SU(2)_L\times SU(2)_R$. The left-handed quarks and leptons are unified into a fundamental representation of $SU(4)_C$, while right-handed quarks and leptons have a separate treatment. The deviations measured in the rare semi-leptonic decays $B\to D^{(*)} τ\barν$ are explained by a scalar leptoquark which couples to right-handed fields and is contained in the $SU(4)_C\times SU(2)_R$ breaking scalar multiplet. The measured deviation of lepton flavor universality in the rare decays $\bar B\to \bar K^{(*)}\ell^+\ell^-$, $\ell=μ,e$ is explained via the $SU(4)_C$ leptoquark gauge boson. The model predicts a new sub-GeV scale sterile neutrino which participates in the anomaly and can be searched for in upcoming neutrino experiments. The theory satisfies the current most sensitive experimental constraints and its allowable parameter regions will be probed as more precise measurements from the LHCb and Belle II experiments become available.

hep-ph↗
arXiv2019

A chiral SU(4) explanation of the $b\to s$ anomalies

We propose a variant of the Pati-Salam model, with gauge group $SU(4)_C\times SU(2)_L\times U(1)_{Y'}$, in which the chiral left-handed quarks and leptons are unified into a $\underline{4}$ of $SU(4)_C$, while the right-handed quarks and leptons have quite a distinct treatment. The $SU(4)_C$ leptoquark gauge bosons can explain the measured deviation of lepton flavour universality in the rare decays: $\bar B \to \bar K^{(*)}\bar\ell\ell, \ell=μ,e$ (taken as a hint of new physics). The model satisfies the relevant experimental constraints and makes predictions for the important $B$ and $τ$ decays. These predictions will be tested at the LHCb and Belle II experiments when increased statistics become available.

hep-ph↗
arXiv2018

More stringent constraints on the unitarised fermionic dark matter Higgs portal

We revisit the simplest model of Higgs portal fermionic dark matter. The dark matter in this scenario is thermally produced in the early universe due to the interactions with the Higgs boson which is described by a non-renormalisable dimension-5 operator. The dark matter-Higgs scattering amplitude grows as $\propto \sqrt{s}$, signalling a breakdown of the effective description of the Higgs-dark matter interactions at large enough (compared to the mass scale $Λ$ of the dimention-5 operator) energies. Therefore, in order to reliably compute Higgs-dark matter scattering cross sections, we employ the K-matrix unitarisation procedure. To account for the desired dark matter abundance, the unitarised theory requires appreaciably smaller $Λ$ than the non-unitarised version, especially for dark matter masses around and below the Higgs resonance, $m_χ\lesssim 65$ GeV, and $m_χ\gtrsim $ few TeV. Consequently, we find that the pure scalar CP-conserving model is fully excluded by current direct dark matter detection experiments.

hep-ph↗