This document proposes a collection of simplified models relevant to the design of new-physics searches at the Large Hadron Collider (LHC) and the characterization of their results. Both ATLAS and CMS have already presented some results in terms of simplified models, and we encourage them to continue and expand this effort, which supplements both signature-based results and benchmark model interpretations. A simplified model is defined by an effective Lagrangian describing the interactions of a small number of new particles. Simplified models can equally well be described by a small number of masses and cross-sections. These parameters are directly related to collider physics observables, making simplified models a particularly effective framework for evaluating searches and a useful starting point for characterizing positive signals of new physics. This document serves as an official summary of the results from the 'Topologies for Early LHC Searches' workshop, held at SLAC in September

We point out that the flavor problem in theories with dynamical electroweak symmetry breaking can be effectively decoupled if the physics above the TeV scale is strongly conformal, and the electroweak order parameter has a scaling dimension d = 1 + ǫ with ǫ ≃ 1/few. There are many restrictions on small values of ǫ: for ǫ ≪ 1, electroweak symmetry breaking requires a finetuning similar to that of the standard model; large-N conformal field theories (including those obtained from the AdS/CFT correspondence) require fine-tuning for d < 2; 'walking technicolor' theories cannot have d < 2, according to gap equation analyses. However, strong small-N conformal field theories with ǫ ≃ 1/few avoid all these constraints, and can give rise to natural dynamical electroweak symmetry breaking with a top quark flavor scale of order 10 1/ǫ TeV, large enough to decouple flavor. Small-N theories also have an acceptably small Peskin-Takeuchi S parameter. This class of theories provides a new direction for dynamical electroweak symmetry breaking without problems from flavor or electroweak precision tests. A possible signal for these theories is a prominent scalar resonance below the TeV scale with couplings similar to a heavy standard model Higgs.

We construct supersymmetric models of SO(10) unification in which the gauge symmetry is broken by orbifold compactification. We find that using boundary conditions to break the gauge symmetry down to SU (3) C ⊗ SU (2) L ⊗ U (1) Y ⊗ U (1) X without leaving unwanted massless states requires at least two extra dimensions, motivating us to work with 6D orbifolds. SO(10) is broken by two operations, each of which induces gauge-breaking to either the Georgi-Glashow, Pati-Salam, or flipped SU (5) ⊗ U (1) subgroups; assigning different unbroken subgroups to the two operations leaves only the standard model gauge group and U (1) X unbroken. The models we build employ extra-dimensional mechanisms for naturally realizing doublet-triplet splitting, suppressing proton decay, and avoiding unwanted grand-unified fermion mass relations. We find some tension between being free of anomalies of the 6D bulk, accommodating a simple mechanism for generating right-handed neutrino masses, and preserving the precise prediction of the weak mixing angle.

We propose signals in the cosmic microwave background to probe the type and spectrum of neutrino masses. In theories that have spontaneous breaking of approximate lepton flavor symmetries at or below the weak scale, light pseudo-Goldstone bosons recouple to the cosmic neutrinos after nucleosynthesis and affect the acoustic oscillations of the electron-photon fluid during the eV era.Deviations from the Standard Model are predicted for both the total energy density in radiation during this epoch, ∆N ν , and for the multipole of the n'th CMB peak at large n, ∆l n . The latter signal is difficult to reproduce other than by scattering of the known neutrinos, and is therefore an ideal test of our class of theories. In many models, the large shift ∆l n ≈ 8n S depends on the number of neutrino species that scatter via the pseudo-Goldstone boson interaction. This interaction is proportional to the neutrino masses, so that the signal reflects the neutrino spectrum.The prediction for ∆N ν is highly model dependent, but can be accurately computed within any given model. It is very sensitive to the number of pseudo-Goldstone bosons, and therefore to the underlying symmetries of the leptons, and is typically in the region of 0.03 < ∆N ν < 1. This signal is significantly larger for Majorana neutrinos than for Dirac neutrinos, and, like the scattering signal, varies as the spectrum of neutrinos is changed from hierarchical to inverse hierarchical to degenerate.