83 research outputs found
Effective Field Theory Amplitudes the On-Shell Way: Scalar and Vector Couplings to Gluons
We use on-shell methods to calculate tree-level effective field theory (EFT)
amplitudes, with no reference to the EFT operators. Lorentz symmetry, unitarity
and Bose statistics determine the allowed kinematical structures. As a
by-product, the number of independent EFT operators simply follows from the set
of polynomials in the Mandelstam invariants, subject to kinematical
constraints. We demonstrate this approach by calculating several amplitudes
with a massive, SM-singlet, scalar () or vector () particle
coupled to gluons. Specifically, we calculate , and
amplitudes, which are relevant for the LHC production and three-gluon decays of
the massive particle. We then use the results to derive the massless-
amplitudes, and show how the massive amplitudes decompose into the
massless-vector plus scalar amplitudes. Amplitudes with the gluons replaced by
photons are straightforwardly obtained from the above.Comment: 25 pages, 3 figures v2: references added, typos fixed and equation
added in appendix, to appear in JHE
Lorentz Violation and Superpartner Masses
We consider Lorentz violation in supersymmetric extensions of the standard
model. We perform a spurion analysis to show that, in the simplest natural
constructions, the resulting supersymmetry-breaking masses are tiny. In the
process, we argue that one of the strongest bounds on Lorentz violation in the
photon Lagrangian, which comes from the absence of birefringence from distant
astrophysical sources, does not apply when Lorentz violation is parametrized by
a single vector.Comment: 13 pages. v3: some comments and a short appendix added to elaborate
on the relation between LV and SUSY breakin
WIMPless Dark Matter from Non-Abelian Hidden Sectors with Anomaly-Mediated Supersymmetry Breaking
In anomaly-mediated supersymmetry breaking (AMSB) models, superpartner masses
are proportional to couplings squared. Their hidden sectors therefore naturally
contain WIMPless dark matter, particles whose thermal relic abundance is
guaranteed to be of the correct size, even though they are not
weakly-interacting massive particles (WIMPs). We study viable dark matter
candidates in WIMPless AMSB models with non-Abelian hidden sectors and
highlight unusual possibilities that emerge in even the simplest models. In one
example with a pure SU(N) hidden sector, stable hidden gluinos freeze out with
the correct relic density, but have an extremely low, but natural, confinement
scale, providing a framework for self-interacting dark matter. In another
simple scenario, hidden gluinos freeze out and decay to visible Winos with the
correct relic density, and hidden glueballs may either be stable, providing a
natural framework for mixed cold-hot dark matter, or may decay, yielding
astrophysical signals. Last, we present a model with light hidden pions that
may be tested with improved constraints on the number of non-relativistic
degrees of freedom. All of these scenarios are defined by a small number of
parameters, are consistent with gauge coupling unification, preserve the
beautiful connection between the weak scale and the observed dark matter relic
density, and are natural, with relatively light visible superpartners. We
conclude with comments on interesting future directions.Comment: 25 page
Duality after Supersymmetry Breaking
Starting with two supersymmetric dual theories, we imagine adding a chiral
perturbation that breaks supersymmetry dynamically. At low energy we then get
two theories with soft supersymmetry-breaking terms that are generated
dynamically. With a canonical Kahler potential, some of the scalars of the
"magnetic" theory typically have negative mass-squared, and the vector-like
symmetry is broken. Since for large supersymmetry breaking the "electric"
theory becomes ordinary QCD, the two theories are then incompatible. For small
supersymmetry breaking, if duality still holds, the magnetic theory analysis
implies specific patterns of chiral symmetry breaking in supersymmetric QCD
with small soft masses.Comment: 6 pages, LaTex, uses moriond.sty (included). Talk presented by Y.S.
at the XXXIIIrd Rencontres de Moriond, Electroweak Interactions and Unified
Theories, Les Arcs, Savoie, France, March 14-21, 199
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