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Register a new userNon-local Higgs actions: Tree-level electroweak constraints and high-energy unitarity
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We consider electroweak symmetry breaking by a certain class of non-local Higgs sectors. Extending previous studies employing the Mandelstam condition, a straight Wilson line is used to make the Higgs action gauge invariant. We show the unitarization of vector-boson scattering for a wide class of non-local actions, but find that the Wilson-line model leads to tree-level corrections to electroweak precision observables, which restrict the parameter space of the model. We also find that Unhiggs models cannot address the hierarchy problem, once the parameters are expressed in terms of low-energy observables.
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We study the five chirality-flipping interactions that appear in the top-Higgs sector at leading order in the standard model effective field theory. We consider constraints from collider observables, flavor physics, and electric-dipole-moment experiments. This analysis results in very competitive constraints from indirect observables when one considers a single coupling at a time. In addition, we discuss how these limits are affected in scenarios in which multiple top-Higgs interactions are generated at the scale of new physics.
We set constraints on the trilinear Higgs boson self-coupling, $lambda_3$, by combining the information coming from the $W$ mass and leptonic effective Weinberg angle, electroweak precision observables, with the single Higgs boson analyses targeting the $gamma gamma,, ZZ^*,, WW^*, ,tau^+ tau^-$ and $bar{b} b$ decay channels and the double Higgs boson analyses in the $bbar{b}bbar{b}, , bbar{b}b tau^+ tau^-$ and $bbar{b}b gamma gamma$ decay channels, performed by the ATLAS collaboration. With the assumption that the new physics affects only the Higgs potential, values outside the interval $ -1.8, lambda_3^{rm SM} < lambda_3 < 9.2 , lambda_3^{rm SM}$ are excluded at $95%$ confidence level. With respect to similar analyses that do not include the information coming from the electroweak precision observables our analysis shows a stronger constraint on both positive and negative values of $lambda_3$.
We calculate the tree-level electroweak precision constraints on a wide class of little Higgs models including: variations of the Littlest Higgs SU(5)/SO(5), SU(6)/Sp(6), and SU(4)^4/SU(3)^4. By performing a global fit to the precision data we find that for generic regions of the parameter space the bound on the symmetry breaking scale f is several TeV, where we have kept the normalization of f constant in the different models. For example, the ``minimal implementation of SU(6)/Sp(6) is bounded by f>3.0 TeV throughout most of the parameter space, and SU(4)^4/SU(3)^4 is bounded by f^2 = f_1^2+f_2^2 > (4.2 TeV)^2. In certain models, such as SU(4)^4/SU(3)^4, a large f does not directly imply a large amount of fine tuning since the heavy fermion masses that contribute to the Higgs mass can be lowered below f for a carefully chosen set of parameters. We also find that for certain models (or variations) there exist regions of parameter space in which the bound on f can be lowered into the range 1-2 TeV. These regions are typically characterized by a small mixing between heavy and standard model gauge bosons, and a small (or vanishing) coupling between heavy U(1) gauge bosons and the light fermions. Whether such a region of parameter space is natural or not is ultimately contingent on the UV completion.
We present a new mechanism to generate large $A$-terms at tree-level in the MSSM through the use of superpotential operators. The mechanism trivially resolves the $A/m^2$ problem which plagues models with conventional, loop-induced $A$-terms. We study both MFV and non-MFV models; in the former, naturalness motivates us to construct a UV completion using Seiberg duality. Finally, we study the phenomenology of these models when they are coupled to minimal gauge mediation. We find that after imposing the Higgs mass constraint, they are largely out of reach of LHC Run I, but they will be probed at Run II. Their fine tuning is basically the minimum possible in the MSSM.
We study electroweak Sudakov corrections in high energy scattering, and the cancellation between real and virtual Sudakov corrections. Numerical results are given for the case of heavy quark production by gluon collisions involving the rates $gg to t bar t, b bar b, t bar b W, t bar t Z, b bar b Z, t bar t H, b bar b H$. Gauge boson virtual corrections are related to real transverse gauge boson emission, and Higgs virtual corrections to Higgs and longitudinal gauge boson emission. At the LHC, electroweak corrections become important in the TeV regime. At the proposed 100 TeV collider, electroweak interactions enter a new regime, where the corrections are very large and need to be resummed.
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