2 A strongly first order EWPT generically requires a modified Higgs - - PowerPoint PPT Presentation

Toyama, Japan

Higgs as a Probe of New Physics 2015

TESTING ELECTROWEAK BARYOGENESIS

VIA DI-HIGGS MEASUREMENTS

Tao Liu

Hong Kong University of Science and Technology

Saturday, February 14, 15

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EW Baryogenesis and Higgs Physics

[A. Cohen et al’93, P. Huet and A. Nelson’96]

Baryon asymmetry may be generated during EW phase transition, if strongly

first order - electroweak baryogenesis (EWBG)

Strongly correlated with Higgs physics: The related CP-phase must enter Higgs couplings A strongly first order EWPT generically requires a modified Higgs potential

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Strongly First Order EWPT

Need to generate a bump for the Higgs potential at high temperature. Not achievable in the SM How to achieve it in BSM physics?

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λ λSM = 1 + 2v4 m2

hΛ2 = 1 + O(1)

V (H) = µ2H†H + κ(H†H)2 + 1 Λ2 (H†H)3

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Mechanism (1): Higher Dim Operators

[A. Noble and M. Perelstein, ’07]

A negative kappa helps achieve EWPT of

strongly first order

Leads to a tri-Higgs coupling at zero

temperature [C. Grojean, G. Servant and J. Wells, ’04]

ξ = hH(Tc)i Tc

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Veff(H, T) = V0(H) + VT 6=0(H, T) + VT =0(H, T) = 1 2 ✓ −µ2 + gφκT 2 24 ◆ H2 − gφκ3/2T 24 √ 2π H3 + λ 4 H4 + VT =0(H, T)

V0(φ, T) = −µ2|H|2 + κ|φ|2|H|2 + η|H|4

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Mechanism (2): BSM Scalar (No Mixing with Higgs)

[A. Noble and M. Perelstein, ’07]

Typically a discrete symmetry is

introduced

The well-known stop-assisted

strongly 1st order EWPT falls into this category

If colored or electrically charged,

may modify Higgs gauge couplings and be probed at HL-LHC or ILC/ CEPC [A. Katz, M. Perelstein, ’14]

Numerically, 20% or more shift in

tri-Higgs coupling

ξ = hH(Tc)i Tc

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λ λSM = 1 35 ✓ λ0v cos3 θ + 1 4(a1 + 2a2x0) cos2 θ sin θ + 1 2a2v cos θ sin2 θ + b3 3 sin3 θ + b4x0 sin3 θ ◆

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Mechanism (3): Higgs-Singlet Mixing

[Profumo, Ramsey-Musolf, Wainwright, Winslow. ’14]

‘

Multiple contributions => broad range of lambda

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λ λSM = 1 35 ✓ λ0v cos3 θ + 1 4(a1 + 2a2x0) cos2 θ sin θ + 1 2a2v cos θ sin2 θ + b3 3 sin3 θ + b4x0 sin3 θ ◆

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Mechanism (3): Higgs-Singlet Mixing

The measurements of the tri-Higgs coupling provides an efficient probe for the EWPT strength and a direct test of the EWBG feasibility

‘

[Profumo, Ramsey-Musolf, Wainwright, Winslow. ’14]

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Di-Higgs Production in the SM

[J. Baglio, A. Djouadi et. al., ’13]

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General Comments

Rare process! Mainly focus on pp -> hh production

[J. Baglio, A. Djouadi et. al., ’13]

Various decay modes have been studied

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Current Focus: pp -> hh

Good: simple topology; clean channel, e.g., hh -> bb+di-photon Not good: negative correlation with lambda; with a positive shift in lambda Lower signal rate Weaker dependence on the tri-Higgs coupling

[R. Frederix et. al., ’14]

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0 < λ λSM < 4

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Positive correlation with tri-Higgs coupling in the SM neighborhood With a positive shift in lambda higher signal rate stronger dependence on the tri-Higgs coupling

Complementary Method: pp -> tthh

[TL, H. Zhang, 1410.1855] [C. Englert et. al.,1409.8074]

∆λ λ =

∆λ λ

• λ/λSM=1

λ λSM exp

⇣

λ/λSM−1 3

⌘

for pp -> tthh (same kinematics is assumed), with

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Illustration: pp -> tthh with hh -> bbbb

pp > hh > bb + di-photon pp > tthh > ttbbbb VS Relatively high Xsection * low Br = 35 ab Relatively low Xsection * high Br = 300 ab

HL-LHC: > 2.0 sigma statistical significance is achievable in searching for

the SM di-Higgs production;

Comparable to that of the pp -> hh -> bb + diphoton (cut-based): 1.3-2.3

sigma [Y. Yao, ’13; V. Barger et. al. ’13; ATL-PHYS-PUB-2014-019] [TL, H. Zhang, 1410.1855]

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Assuming that NP enters tri-Higgs coupling only, if any Mechanism (1) and (2): HL-LHC shows a good sensitivity Mechanism (3): HL-LHC shows some sensitivity

Tri-Higgs Coupling Measurement via pp -> tthh

[TL, H. Zhang, 1410.1855]

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Outlook

Further improvements: e.g., consider pp -> tt hh -> ttWW bb: loses some signal

rate, gains from same-sign leptons [suggested by A. Juste]

A probe for new physics, e.g., ; Certainly needs to think how to disentangle various contributions to the di-

Higgs production

What are the gains from 100 TeV pp collider. To what extent can we test EWPT

• f strongly first order (by combining with the other channels)?

t¯ thh Λ

[R. Frederix et. al., ’14]

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Tank yo!

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General Comments

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