Higgs boson production at LHC as a probe of littlest Higgs models with T-parity

Lei Wang

ITP

LW, J. M. Yang, PRD77, 015020 (2008)

Outline Motivation Littlest Higgs models with T-parity Single Higgs boson production via gluon-gluon

fusion Higgs-pair production via gluon-gluon fusion A Higgs boson in association with a pair of top

quarks at LHC Conclusions

Assume SM valid up to some momentum scale . Then the largest

radiative corrections to the Higgs mass are from the top quark loop:

Motivation

Maximum scale for new physics if we allow 10% fine tuning:

Ann. Rev. Nucl. Part. Sci.55, 229-270 (2005),M. Schmaltz, D. Tucker-Smith

The TeV-scale quark greatly affects the Higgs boson production processes which are dominated by top quark:

Single Higgs boson production via gluon-gluon fusion

Higgs-pair production via gluon-gluon fusion

A Higgs boson in association with a pair of top quarks at LHC

Even these Higgs boson production processes can be as a probe of different little Higgs models.

Existence of new TeV-scale quark with specific couplings to the Higgs so that the loops involving the TeV-scale quark cancel the quadratic divergence from the top quark loop .

A characteristic feature of little Higgs models:

PRD69, 075002 (2004), M. Perelstein, M. E. PeskinJHEP 0601,099, (2006), T. Han, H. E. Logan, L. T. Wang

Higgs boson is a pseudo-Goldstone boson

Combination of both couplings break global symmetry protecting Higgs mass from radiative corrections.

No 1-loop quadratic divergence!

Little Higgs mechanism(collective symmetry breaking)

Littlest Higgs models with T-parity

Littlest Higgs model

Based on non-linear sigma model.

Global symmetry:

Gauge symmetries:

(5) (5)SU SO

1 2(2) (1) (2) (1) (2) (1) (1)EMSU U SU U SU U U

Higgs is an exact Goldstone boson under either SU(3) global symmetry. Combination of both couplings breaks global symmetry enough to allow Higgs to become a pseudo-Goldstone boson.

(5) / (5)SU SO

JHEP 0207, 034 (2002), N. Arkani-Hamed, A. G. Cohen, E. Katz, A.E. Nelson

The characteristic difference between littlest Higgs models with T-parity

We comparatively study two different littlest Higgs models with T-parity. The characteristic difference is the new heavy T-quark, which cancels the quadratic divergence from the top quark loop.

Model-I: T-quark is T-even under T-parity

Model-II: T-quark is T-odd under T-parity PRD74, 055001 (2006), H. C. Cheng, I. Low, L. T. Wang

JHEP 0309, 051, 2003, H. C. Cheng, I. Low

Top-quark Yukawa interaction

1(3)SU T-parity

T-parity

Under T-parity:

Model-IJHEP 0309, 051 (2003), H. C. Cheng, I. LowPRD71, 035016 (2005), J. Hubisz, P. Meade

where i, j, k summed over 1, 2, 3 whereas x, y summed over 4, 5.

2(3)SU

Higgs interaction and mass term for top quark and partners:

The t and T are the linear combination of and .u U

where ‘+’ represents T-even and ‘-’ represents T-odd.

PRD69, 075002 (2004), M. Perelstein, M. E. PeskinJHEP 0601,099, (2006), T. Han, H. E. Logan, L. T. Wang

For , the 1-loop quadratic divergences can be canceled.

where .

Model-II

where i, j, k summed over 1, 2, 3 whereas x, y summed over 4, 5.

where l, m, n summed over 3, 4, 5 whereas r, s summed over 1, 2.

PRD74, 055001 (2006), H. C. Cheng, I. Low, L. T. Wang

Top-quark Yukawa interaction

The will introduce mixing between the light T-even and the heavy T-even fermions, which can be removed by the additional interactions,

T-parity

T-parity

Under T-parity:

1(3)SU 2(3)SU

The t and are the linear combination of and .u U T

For , Higgs interaction and mass term for top quark and partners:

The relation provides an important test of the little Higgs mechanism.

Higgs interaction and mass term for the other new quarks:

Model-I: three generations

Model-II:

The first two generations

The third generation

where .

Single-Higgs via gluon-gluon fusion

In the SM, top-quark loop dominates the amplitude.

In the model-I and model-II, the corrections are from the top-quark loops through modified coupling and loops of new T-even and T-odd quarks.

The results are not sensitive to the heavy quark mass. We take

in model-I and in model-II, and mh=150GeV. New particle scale f can be as low as 500GeV.

This process was studied in Model-I :

PLB640, 263 (2006), C. R. Chen, K. Tobe, C. P.Yuan.

1 2

JHEP 0601, 135 (2006), J. Hubisz, P. Meade, A. Noble, M. Perelstein

Single Higgs production via gluon-gluon fusion at LHC

The production cross section can be significantly suppressed.

Higgs-pair production via gluon-gluon fusion at LHC

In the SM, top-quark loop dominates the amplitude.

In the model-I and model-II, the corrections are from the top-quark loops through modified coupling and the tree-level coupling. The loops of new T-even and T-odd quarks also come into play.

htt hhtt

Higgs-pair production via gluon-gluon fusion at LHC

The production cross section can be significantly enhanced.

production at LHC

At tree-level, the correction is from the modified coupling.

ht t

htt

production at LHCht t

The production cross section can be significantly suppressed.

Conclusions The Higgs boson production processes which are dominated by to

p quark: 1. Single Higgs boson production via gluon-gluon fusion, 2. Higgs-pair production via gluon-gluon fusion, 3. A Higgs boson in association with a pair of top quarks at LHC.

Model-I and model-II can alter the SM cross sections sizably and their corrections also differ significantly. Therefore, the Higgs boson productions at the LHC may shed some light on these two models or even distinguish them.

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