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.

We analyze the loop induced decays of the Higgs boson into pairs of gluons and photons in the Littlest Higgs model. We find that the deviation of the partial widths for these decays relative to their Standard Model values scales with 1/f 2 , where f ∼ TeV is the mass scale of the new heavy particles in the model. For f = 1 TeV, Γ(H → gg) is reduced by 6 − 10% and Γ(H → γγ) is reduced by 5 − 7% compared to their Standard Model values. While the LHC and a linear e + e − collider would be sensitive to these deviations only for relatively low values of f < ∼ 650 GeV, a photon collider could probe the deviation in Γ(H → γγ) up to f < ∼ 1.1 (0.7) TeV at the 2 (5) σ

Many beyond the standard model theories include a stable dark matter candidate that yields missing or invisible energy in collider detectors. If observed at the CERN Large Hadron Collider, we must determine if its mass and other properties (and those of its partners) predict the correct dark matter relic density. We give a new procedure for determining its mass with small error. DOI: 10.1103/PhysRevLett.100.252001 PACS numbers: 13.85.Qk, 14.80.Ly One of the most dramatic possibilities for the Large Hadron Collider (LHC) is the observation of events with large missing energy compatible with the production of a stable, weakly interacting particle that could explain the Universe's relic dark matter content. Many beyond the standard model (SM) theories contain such a particle, denoted N. In particular, in the minimal supersymmetric standard model (MSSM) the lightest neutralino~0 1 is stable if R parity is conserved. Each LHC event must contain two N's that each emerge at the end of a chain decay. For example, in the MSSM, a large production rate is associated with the squark pair,qq , production, and eachq can have substantial probability to decay viaq ! q~0 2 ! q'' ! q' '~0 1 (' e; ; ), where~0 2 andl are the second lightest neutralino and slepton, respectively. More generally, we will use the notation Z ! 7 Y ! 7 5 X ! 7 5 3 1 N , where particles 7, 5, and 3 are standard model jets or leptons and Z, Y, and X are intermediate on-shell resonances. This event structure is illustrated in Fig. 1. This Letter gives a procedure for accurately determining M Z , M Y , M X , and M N for this topology.Many mass determination procedures examine only one decay chain at a time [1][2][3][4]. This often does not allow one to solve for the event's missing momenta. An exception is a very long decay chain starting from the gluino [2]. Considering both decay chains simultaneously gives us more information and allows a better determination of the masses [5][6][7]. For the decay chains of Fig. 1, if all particles can be correctly located on the decay chains and there are no experimental effects, by considering two events we can solve for all the 4-momenta in both events and determine all the masses up to a discrete ambiguity. After examining a small number of event pairings, a unique solution will emerge.Assuming we can isolate LHC events with the topology in Fig. 1 and using m N m N

We examine in a model-independent manner the measurements that can be performed at B-factories with sensitivity to dark matter. If a singlet scalar, pseudo-scalar, or vector is present and mediates the Standard Model -dark matter interaction, it can mediate invisible decays of quarkonium states such as the Υ, J/Ψ, and η. Such scenarios have arisen in the context of supersymmetry, extended Higgs sectors, solutions the supersymmetric µ problem, and extra U(1) gauge groups from grand unified theories and string theory. Existing Bfactories running at the Υ(4S) can produce lower Υ resonances by emitting an Initial State Radiation (ISR) photon. Using a combination of ISR and radiative decays, the initial state of an invisibly decaying quarkonium resonance can be tagged, giving sensitivity to the spin and CP-nature of the particle that mediates standard model-dark matter interactions. These measurements can discover or place strong constraints on dark matter scenarios where the dark matter is approximately lighter than the b-quark. collected at the Υ(4S), the B-factories can limit BR(Υ(1S) → invisible) < ∼ 0.1%.