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Vector Higgs-Portal Dark Matter and Fermi-LAT Gamma Ray Line. Ki -Young Choi , Hyun Min Lee, Osamu Seto June 2013 Presented by Randy Lafler. Outline. Observation Model Lagrangian Feynman Diagrams Conclusions. Observation.

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Vector higgs portal dark matter and fermi lat gamma ray line

Vector Higgs-Portal Dark Matter and Fermi-LAT Gamma Ray Line

Ki-Young Choi, Hyun Min Lee,

Osamu Seto

June 2013

Presented by Randy Lafler


  • Observation

  • Model

  • Lagrangian

  • Feynman Diagrams

  • Conclusions


  • In the Fermi-LAT data a Gamma Ray Line Spectrum was found at Eγ=130 GeV

    • Narrow Spectral Lines originating from the Galactic Center

  • Signature independently confirmed by other groups and Officially Investigated By Fermi-LAT Collaboration

    • Peak shifted to 135 GeV

  • Possible Explanations

    • Monoenergetic Pulsar Winds, Fermi Bubble, or Instrument Effects including Earth Limb Signal

Proposed explanation
Proposed Explanation

  • Fermi-LAT Collaboration and H.E.S.S Collaboration reported only upper bound on annihilation X-Section of WIMPs

    • Could be DM

  • DM is neutral

    • Cannot annihilate into γ’s at tree level

    • Generation of γ’s must happen via loops of charged particles which DM is directly or indirectly coupled

    • Annihilation X-Section into γ’s is much suppressed compared to other tree level annihilation channels

    • In order for Large Branching Fraction, DM must have Large Coupling to New Charged Particle Running in Loops


  • Vector DM couples to SM via Higgs Portal Interactions

  • Gauge Sector: SU(3)C x SU(2)L x U(1)Y x U(1)x

  • Introduce a Complex Scalar Field S1

    • It obtains a Vacuum Expectation Value (VEV) and Spontaneously Breaks the Extra U(1)x Gauge Symmetry

  • To have DM annihilation into a Photon Pair

    • Introduce SU(2) Singlet Charged Scalar S2+

    • Y=1

    • Neutral under U(1)x

  • Higgs Doublet φ and All SM particles are Neutral under U(1)x

  • DM is the Gauge Boson of U(1)x after Spontaneously Broken by VEV of Hidden Higgs Field at RenormalizableLevel (S1)

  • Ensure stability of VDM

    • When U(1)x is broken there is a remnant Symmetry Z2 under which S1 S1* and X  -X

  • DM predominately annihilates into W and Z through s-channel exchange of h and H Higgs Bosons in Early Universe

    • Ensure observed Thermal Relic Abundance of DM

Model lagrangian
Model Lagrangian

  • Fuv = duXv - dvXu

  • Du S1 = (du – igxXu)S1

    • Covariant Derivatives (CD) with respect to U(1)x and U(1)Y

    • After EW Symmetry Breaking, D2S2 is reduced to CD with respect to U(1)em Symmetry

  • Final term

    • Li is SM lepton doublet with flavor index i = 1,2,3

    • C is Charge Conjugation Operator

    • Dot denotes SU(2) Antisymmetric product

    • Lepton Flavor Violation because fij is Antisymmetric

    • S2+  li+/- +

Mass eigenstates h and h
Mass Eigenstates h and H

  • Expand Higgs Doublet φand S1 Fields around EW vacuum

    • <φ>=v/sqrt(2) and <S1> =vs/sqrt(2)

    • v = 246 GeV

  • For small sin(α)

    • h ~ φ; SM Higgs particle

    • H ~ φs ; Singlet

Vdm annihilation to w z
VDM Annihilation to W,Z

  • XX  Zγ will produce additional Gamma Ray Line at Eγ=114GeV

    • Flux is reduced by 0.21

  • XXZZ

    • Flux is negligible

Vdm annihilation diagram to photons

Annihilation of VDM to Photon Pair at loop level

VDM Annihilation Diagram to Photons

Explanation of observations
Explanation of Observations

  • When H has small coupling to W and Z but Large (Quartic) Coupling to Charged Scalar S2+

    • Diphoton production from DM annihilation takes larger branching fraction of annihilation X-Section

  • Annihilation into WW or ZZ must now be suppressed to prevent generation of excess Continuum Photons

  • Explains both Relic DM Density and Gamma Ray Line

  • S2+ Lepton Coupling Matrix fij< O(10-2) to be consistent with EW Precision Measurements


  • Mx=MH/2=135 GeV

    • MH = 270 GeV

  • To have Gamma Ray Line Spectrum at Eγ=135Gev

    • <σv>XX γγ = 1.1x10-10 GeV-2

  • Gamma Ray Line at Eγ114 GeV

    • 0.21 reduced flux

  • Lepton Flavor Violation from Charged Scalar S2+ decay


  • Renormalizable Model of Vector DM

  • Extra SU(1)x Gauge Boson is DM candidate and interacts with SM particles through Higgs Portal

  • For Quartic Coupling between Singlet Scalar H and Charged Scalar S2+, DM annihilation into photons has sizable Branching Fraction

  • Finding Singlet Scalar H will be hard to find due to small mixing with the Higgs

  • S2 would be accessible at LHC due to distinct signature that 2 oppositely signed Leptons of different flavors are equally produced from S2 decay


  • Choi, Ki-Young, Hyun Hyun Lee, and Osamu Seto. "Vector Higgs-Portal Dark Matter and Fermi-Lat Gamma Ray Line." PHYSICAL REVIEW (2013)