We study the low-energy phenomenology of the little Higgs model. We first discuss the linearized effective theory of the ''littlest Higgs model'' and study the low-energy constraints on the model parameters. We identify sources of the corrections to low-energy observables, discuss model-dependent arbitrariness, and outline some possible directions of extensions of the model in order to evade the precision electroweak constraints. We then explore the characteristic signatures to test the model in the current and future collider experiments. We find that the CERN LHC has great potential to discover the new SU(2) gauge bosons and the possible new U(1) gauge boson to the multi-TeV mass scale. Other states such as the colored vectorlike quark T and doubly charged Higgs boson ⌽ ϩϩ may also provide interesting signals. At a linear collider, precision measurements on the triple gauge boson couplings could be sensitive to the new physics scale of a few TeV. We provide a comprehensive list of the linearized interactions and vertices for the littlest Higgs model in the appendices.

Completely natural electroweak symmetry breaking is easily achieved in supersymmetric models if there is a SM-like Higgs boson, h, with m h < ∼ 100 GeV. In the minimal supersymmetric model, such an h decays mainly to bb and is ruled out by LEP constraints. However, if the MSSM Higgs sector is expanded so that h decays mainly to still lighter Higgs bosons, e.g. h → aa, with Br(h → aa) > 0.7, and if ma < 2m b , then the LEP constraints are satisfied. In this letter, we show that in the next-tominimal supersymmetric model the above h and a properties (for the lightest CP-even and CP-odd Higgs bosons, respectively) imply a lower bound on Br(Υ → γa) that dedicated runs at present (and future) B factories can explore.Low energy supersymmetry remains one of the most attractive solutions to the naturalness / hierarchy problem of the Standard Model (SM). However, the minimal supersymmetric model (MSSM), containing exactly two Higgs doublets, suffers from the "µ problem" and requires rather special parameter choices in order that the light Higgs mass is above LEP limits without electroweak symmetry breaking being "fine-tuned", i.e. highly sensitive to supersymmetry-breaking parameters chosen at the grand-unification scale. Both problems are easily solved by adding Higgs (super) fields to the MSSM. For generic SUSY parameters well-below the TeV scale, finetuning is absent [1] and a SM-like h is predicted with m h < ∼ 100 GeV. Such an h can avoid LEP limits on the tightly constrained e + e − → Z +b ′ s channel if Br(h → bb) is small by virtue of large Br(h → aa), where a is a new light (typically CP-odd) Higgs boson, and m a < 2m b so that a → bb is forbidden [2]. The perfect place to search for such an a is in Upsilon decays, Υ → γa. The simplest MSSM extension, the next-to-minimal supersymmetric model (NMSSM), naturally predicts that the lightest h and a, h 1 and a 1 , have all the right features [1,2,3,4,5]. In this letter, we show that large Br(h 1 → a 1 a 1 ) implies, at fixed m a1 , a lower bound on Br(Υ → γa 1 ) (from now on, Υ is the 1S resonance unless otherwise stated) that is typically within reach of present and future B factories.In the NMSSM, a light a 1 with substantial Br(h 1 → a 1 a 1 ) is a very natural possibility for m Z -scale soft parameters developed by renormalization group running starting from U (1) R symmetric GUT-scale soft parameters [5]. (See also [6,7] for discussions of the light a 1 scenario.) The fine-tuning-preferred m h1 ∼ 100 GeV (for tan β > ∼ f ew) gives perfect consistency with precision electroweak data and the reduced Br(h 1 → bb) ∼ 0.09 − 0.15 explains the ∼ 2.3σ excess at LEP in the Zbb channel at M bb ∼ 100 GeV. The motivation for this scenario is thus very strong.Hadron collider probes of the NMSSM Higgs sector are problematical. The h 1 → a 1 a 1 → 4τ (2m τ < m a1 < 2m b ) or 4 jets (m a1 < 2m τ ) signal is a very difficult one at the Tevatron and very possibly at the LHC [8,9,10,11]. Higgs discovery or, at the very least, certification of a marginal LHC Higgs signal will requi...

We assess the extent to which the NMSSM can allow for light dark matter in the 2 GeV < ∼ m χ 0 1 < ∼ 12 GeV mass range with correct relic density and large spin-independent direct-detection cross section, σSI , in the range suggested by CoGeNT and DAMA. For standard assumptions regarding nucleon s-quark content and cosmological relic density, ρ, we find that the NMSSM falls short by a factor of about 10 to 15 (3 to 5) without (with) significant violation of the current (g − 2)µ constraints.

We systematically discuss the consequences of genuine dimension-six Higgs operators. These operators are not subject to stringent constraints from electroweak precision data. However, they can modify the couplings of the Higgs boson to electroweak gauge bosons and, in particular, the Higgs self-interactions. We study the sensitivity to which those couplings can be probed at future e + e − linear colliders in the sub-TeV and in the multi-TeV range. We find that for √ s = 500 GeV with a luminosity of 1 ab −1 the anomalous W W H and ZZH couplings may be probed to about the 0.01 level, and the anomalous HHH coupling to about the 0.1

We describe a kinematic method which is capable of determining the overall mass scale in SUSY-like events at a hadron collider with two missing (dark matter) particles. We focus on the kinematic topology in which a pair of identical particles is produced with each decaying to two leptons and an invisible particle (schematically, pp → Y Y + jets followed by each Y decaying via Y → ℓX → ℓℓ ′ N where N is invisible). This topology arises in many SUSY processes such as squark and gluino production and decay, not to mention tt di-lepton decays. In the example where the final state leptons are all muons, our errors on the masses of the particles Y , X and N in the decay chain range from 4 GeV for 2000 events after cuts to 13 GeV for 400 events after cuts. Errors for mass differences are much smaller. Our ability to determine masses comes from considering all the kinematic information in the event, including the missing momentum, in conjunction with the quadratic constraints that arise from the Y , X and N mass-shell conditions. Realistic missing momentum and lepton momenta uncertainties are included in the analysis.