Two-Point Functions and S-Parameter in QCD-like Theories

We calculated the vector, axial-vector, scalar and pseudo-scalar two-point functions up to two-loop level in the low-energy effective field theory for three different QCD-like theories. In addition we also calculated the pseudo-scalar decay constant $G_M$. The QCD-like theories we used are those with fermions in a complex, real or pseudo-real representation with in general n flavours. These case correspond to global symmetry breaking pattern of $SU(n)_L\times SU(n)_R\to SU(n)_V$, $SU(2n)\to SO(2n)$ or $SU(2n)\to Sp(2n)$. We also estimated the S parameter for those different theories.Comment: 29 page

EWPD Constraints on Flavor Symmetric Vector Fields

Electroweak precision data constraints on flavor symmetric vector fields are determined. The flavor multiplets of spin one that we examine are the complete set of fields that couple to quark bi-linears at tree level while not initially breaking the quark global flavor symmetry group. Flavor safe vector masses proximate to, and in some cases below, the electroweak symmetry breaking scale are found to be allowed. Many of these fields provide a flavor safe mechanism to explain the t tbar forward backward anomaly, and can simultaneously significantly raise the allowed values of the Standard Model Higgs mass consistent with electroweak precision data.Comment: Matches version published in JHE

Probing for Invisible Higgs Decays with Global Fits

We demonstrate by performing a global fit on Higgs signal strength data that large invisible branching ratios Br_{inv} for a Standard Model (SM) Higgs particle are currently consistent with the experimental hints of a scalar resonance at the mass scale m_h ~ 124 GeV. For this mass scale, we find Br_{inv} < 0.64 (95 % CL) from a global fit to individual channel signal strengths supplied by ATLAS, CMS and the Tevatron collaborations. Novel tests that can be used to improve the prospects of experimentally discovering the existence of a Br_{inv} with future data are proposed. These tests are based on the combination of all visible channel Higgs signal strengths, and allow us to examine the required reduction in experimental and theoretical errors in this data that would allow a more significantly bounded invisible branching ratio to be experimentally supported. We examine in some detail how our conclusions and method are affected when a scalar resonance at this mass scale has couplings deviating from the SM ones.Comment: 32pp, 15 figures v2: JHEP version, ref added & comment added after Eq.

On theories of enhanced CP violation in B_s,d meson mixing

The DO collaboration has measured a deviation from the standard model (SM) prediction in the like sign dimuon asymmetry in semileptonic b decay with a significance of 3.2 sigma. We discuss how minimal flavour violating (MFV) models with multiple scalar representations can lead to this deviation through tree level exchanges of new MFV scalars. We review how the two scalar doublet model can accommodate this result and discuss some of its phenomenology. Limits on electric dipole moments suggest that in this model the coupling of the charged scalar to the right handed u-type quarks is suppressed while its coupling to the d-type right handed quarks must be enhanced. We construct an extension of the MFV two scalar doublet model where this occurs naturally.Comment: 10 pages, 7 figures, v3 final JHEP versio

Meson-meson Scattering in QCD-like Theories

We discuss meson-meson scattering at next-to-next-to-leading order in the chiral expansion for QCD-like theories with general $n$ degenerate flavours for the cases with a complex, real and pseudo-real representation. I.e. with global symmetry and breaking pattern $SU(n)_L\times SU(n)_R\to SU(n)_V$, $SU(2n)\to SO(2n)$ and $SU(2n)\to Sp(2n)$. We obtain fully analytical expressions for all these cases. We discuss the general structure of the amplitude and the structure of the possible intermediate channels for all three cases. We derive the expressions for the lowest partial wave scattering length in each channel and present some representative numerical results. We also show various relations between the different cases in the limit of large $n$.Comment: 61 page

Pure-glue hidden valleys through the Higgs portal

We consider the possibility that the Higgs boson can act as a link to a hidden sector in the context of pure-glue hidden valley models. In these models the standard model is weakly coupled, through loops of heavy messengers fields, to a hidden sector whose low energy dynamics is described by a pure-Yang-Mills theory. Such a hidden sector contains several metastable hidden glueballs. In this work we shall extend earlier results on hidden valleys to include couplings of the messengers to the standard model Higgs sector. The effective interactions at one-loop couple the hidden gluons to the standard model particles through the Higgs sector. These couplings in turn induce hidden glueball decays to fermion pairs, or cascade decays with multiple Higgs emission. The presence of effective operators of different mass dimensions, often competing with each other, together with a great diversity of states, leads to a great variability in the lifetimes and decay modes of the hidden glueballs. We find that most of the operators considered in this paper are not heavily constrained by precision electroweak physics, therefore leaving plenty of room in the parameter space to be explored by the future experiments at the LHC.Comment: 44 pages, 16 figures. Major revision for JHEP, corrected an error in Eq. 5.1, comments adde

Exploring the Higgs Portal with 10/fb at the LHC

We consider the impact of new exotic colored and/or charged matter interacting through the Higgs portal on Standard Model Higgs boson searches at the LHC. Such Higgs portal couplings can induce shifts in the effective Higgs-gluon-gluon and Higgs-photon-photon couplings, thus modifying the Higgs production and decay patterns. We consider two possible interpretations of the current LHC Higgs searches based on ~ 5/fb of data at each detector: 1) a Higgs boson in the mass range (124-126) GeV and 2) a `hidden' heavy Higgs boson which is underproduced due to the suppression of its gluon fusion production cross section. We first perform a model independent analysis of the allowed sizes of such shifts in light of the current LHC data. As a class of possible candidates for new physics which gives rise to such shifts, we investigate the effects of new scalar multiplets charged under the Standard Model gauge symmetries. We determine the scalar parameter space that is allowed by current LHC Higgs searches, and compare with complementary LHC searches that are sensitive to the direct production of colored scalar states.Comment: 27 pages, 11 figures; v2: references added, correction to scalar form factor, numerical results updated with Moriond 2012 data, conclusions unchange

Composite Higgs Search at the LHC

The Higgs boson production cross-sections and decay rates depend, within the Standard Model (SM), on a single unknown parameter, the Higgs mass. In composite Higgs models where the Higgs boson emerges as a pseudo-Goldstone boson from a strongly-interacting sector, additional parameters control the Higgs properties which then deviate from the SM ones. These deviations modify the LEP and Tevatron exclusion bounds and significantly affect the searches for the Higgs boson at the LHC. In some cases, all the Higgs couplings are reduced, which results in deterioration of the Higgs searches but the deviations of the Higgs couplings can also allow for an enhancement of the gluon-fusion production channel, leading to higher statistical significances. The search in the H to gamma gamma channel can also be substantially improved due to an enhancement of the branching fraction for the decay of the Higgs boson into a pair of photons.Comment: 32 pages, 16 figure

Hiding a Heavy Higgs Boson at the 7 TeV LHC

A heavy Standard Model Higgs boson is not only disfavored by electroweak precision observables but is also excluded by direct searches at the 7 TeV LHC for a wide range of masses. Here, we examine scenarios where a heavy Higgs boson can be made consistent with both the indirect constraints and the direct null searches by adding only one new particle beyond the Standard Model. This new particle should be a weak multiplet in order to have additional contributions to the oblique parameters. If it is a color singlet, we find that a heavy Higgs with an intermediate mass of 200 - 300 GeV can decay into the new states, suppressing the branching ratios for the standard model modes, and thus hiding a heavy Higgs at the LHC. If the new particle is also charged under QCD, the Higgs production cross section from gluon fusion can be reduced significantly due to the new colored particle one-loop contribution. Current collider constraints on the new particles allow for viable parameter space to exist in order to hide a heavy Higgs boson. We categorize the general signatures of these new particles, identify favored regions of their parameter space and point out that discovering or excluding them at the LHC can provide important indirect information for a heavy Higgs. Finally, for a very heavy Higgs boson, beyond the search limit at the 7 TeV LHC, we discuss three additional scenarios where models would be consistent with electroweak precision tests: including an additional vector-like fermion mixing with the top quark, adding another U(1) gauge boson and modifying triple-gauge boson couplings.Comment: 42 pages, 12 figure