A
bstract
The leading contributions from heavy new physics to Higgs processes can be captured in a model-independent way by dimension-six operators in an effective Lagrangian approach. We present a ...complete analysis of how these contributions affect Higgs couplings. Under certain well-motivated assumptions, we find that 8 CP-even plus 3 CP-odd Wilson coefficients parametrize the main impact in Higgs physics, as all other coefficients are constrained by non-Higgs SM measurements. We calculate the most relevant anomalous dimensions for these Wilson coefficients, which describe operator mixing from the heavy scale down to the electroweak scale. This allows us to find the leading-log corrections to the predictions for the Higgs couplings in specific models, such as the MSSM or composite Higgs, which we find to be significant in certain cases.
We characterize models where electroweak symmetry breaking is driven by two light Higgs doublets arising as pseudo-Nambu–Goldstone bosons of new dynamics above the weak scale. They represent the ...simplest natural two Higgs doublet alternative to supersymmetry. We construct their low-energy effective Lagrangian making only few specific assumptions about the strong sector. These concern their global symmetries, their patterns of spontaneous breaking and the sources of explicit breaking. In particular we assume that all the explicit breaking is associated with the couplings of the strong sector to the Standard Model fields, that is gauge and (proto)-Yukawa interactions. Under those assumptions the scalar potential is determined at lowest order by very few free parameters associated to the top sector. Another crucial property of our scenarios is the presence of a discrete symmetry, in addition to custodial SO(4), that controls the
T-parameter. That can either be simple
CP or a
Z
2
that distinguishes the two Higgs doublets. Among various possibilities we study in detail models based on SO(6)/SO(4)
×
SO(2), focussing on their predictions for the structure of the scalar spectrum and the deviations of their couplings from those of a generic renormalizable two Higgs doublet model.
In Effective Field Theories (EFTs) with higher-dimensional operators many anomalous dimensions vanish at the one-loop level. With the use of supersymmetry, and a classification of the operators ...according to their embedding in super-operators, we are able to understand why many of these anomalous dimensions are zero. The key observation is that one-loop contributions from superpartners trivially vanish in many cases under consideration, making the superfield formalism a powerful tool even for non-supersymmetric models. We show this in detail in a simple U(1) model with a scalar and fermions, and explain how to extend this to SM EFTs and the QCD Chiral Lagrangian. This provides an understanding of why most “current–current” operators do not renormalize “loop” operators at the one-loop level, and allows to find the few exceptions to this ubiquitous rule.
We present a simple
N=1 five-dimensional model where the fifth dimension is compactified on the orbifold
S
1/
Z
2
. Non-chiral matter lives in the bulk of the fifth dimension (five dimensions) while ...chiral matter lives on the fixed points of the orbifold (four-dimensional boundaries). The massless sector constitutes the Minimal Supersymmetric Standard Model while the massive modes rearrange in
N=2 supermultiplets. After supersymmetry breaking by the Scherk-Schwarz mechanism the zero modes can be reduced to the non-supersymmetric Standard Model.
We consider the possibility of gauge bosons living in the recently proposed five-dimensional theory with localized gravity. We study the mass spectrum of the Kaluza-Klein (KK) excitations of the ...gauge fields and calculate their couplings to the boundaries of the fifth dimension. We find a different behaviour from the case of the graviton. In particular, we find that the massless mode is not localized in the extra dimension and that the KK excitations have sizeable couplings to the two boundaries. We also discuss possible phenomenological implications for the case of the standard model gauge bosons.
Based on the AdS/CFT correspondence we study the breaking of the chiral symmetry in QCD using a simple five-dimensional model. The model gives definite predictions for the spectrum of vector mesons, ...their decay constants and interactions as a function of one parameter related to the quark condensate. We calculate the coefficients
L
i
of the low-energy QCD chiral Lagrangian, as well as other physical quantities for the pions. All the predictions are shown to be in good agreement with the experimental data. We also show that they are robust under modifications of the 5D metric in the IR, and that some of them arise as a consequence of the higher-dimensional gauge symmetry. For example, at the tree-level, we find
M
ρ
≃
3
g
ρ
π
π
F
π
,
F
ρ
≃
3
F
π
and
BR
(
a
1
→
π
γ
)
=
0
.
We study the sparticle spectroscopy and electroweak breaking of theories where supersymmetry is broken by compactification (Scherk-Schwarz mechanism) at a TeV The evolution of the soft terms above ...the compactification scale and the resulting sparticle spectrum are very different from those of the usual MSSM and gauge-mediated theories. This is traced to the softness of the Scherk-Schwarz mechanism which leads to scalar sparticle masses that are only logarithmically sensitive to the cutoff starting at two loops. As a result, the mass-squareds of the squarks and sleptons are a loop factor smaller than those of the gauginos. In addition, the mechanism is very predictive and the sparticle spectrum depends on just two new parameters. A significant advantage of this mechanism relative to gauge mediation is that a Higgsino mass
μ ≈
M
susy
is automatically generated when supersymmetry is broken. Our analysis applies equally well to theories where the cutoff is near a TeV or
M
Pℓ
or some intermediate scale. We also use these observations to show how we may obtain compactification radii which are hierarchically larger than the fundamental cutoff scale.
The strongly-interacting light Higgs Giudice, Gian Francesco; Grojean, Christophe; Pomarol, Alex ...
The journal of high energy physics,
06/2007, Letnik:
2007, Številka:
6
Journal Article
PDF
