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

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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

- 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

- 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

Model

- 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

- 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

- 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

- XX Zγ will produce additional Gamma Ray Line at Eγ=114GeV
- Flux is reduced by 0.21
- XXZZ
- Flux is negligible

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

Predictions

- 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

Conclusion

- 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

References

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

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