1,737 research outputs found
The Minimal Moose for a Little Higgs
Recently a new class of theories of electroweak symmetry breaking have been
constructed. These models, based on deconstruction and the physics of theory
space, provide the first alternative to weak-scale supersymmetry with naturally
light Higgs fields and perturbative new physics at the TeV scale. The Higgs is
light because it is a pseudo-Goldstone boson, and the quadratically divergent
contributions to the Higgs mass are cancelled by new TeV scale ``partners'' of
the {\em same} statistics. In this paper we present the minimal theory space
model of electroweak symmetry breaking, with two sites and four link fields,
and the minimal set of fermions. There are very few parameters and degrees of
freedom beyond the Standard Model. Below a TeV, we have the Standard Model with
two light Higgs doublets, and an additional complex scalar weak triplet and
singlet. At the TeV scale, the new particles that cancel the 1-loop quadratic
divergences in the Higgs mass are revealed. The entire Higgs potential needed
for electroweak symmetry breaking--the quartic couplings as well as the
familiar negative mass squared--can be generated by the top Yukawa coupling,
providing a novel link between the physics of flavor and electroweak symmetry
breaking.Comment: 15 pages. References added. Included clarifying comments on the
origin of quartic couplings, and on power-counting. More elegant model for
generating Higgs potential from top Yukawa coupling presente
Mooses, Topology and Higgs
New theories of electroweak symmetry breaking have recently been constructed
that stabilize the weak scale and do not rely upon supersymmetry. In these
theories the Higgs boson is a weakly coupled pseudo-Goldstone boson. In this
note we study the class of theories that can be described by theory spaces and
show that the fundamental group of theory space describes all the relevant
classical physics in the low energy theory. The relationship between the low
energy physics and the topological properties of theory space allow a
systematic method for constructing theory spaces that give any desired low
energy particle content and potential. This provides us with tools for
analyzing and constructing new theories of electroweak symmetry breaking.Comment: 16 pages, 11 figure
Phenomenology of Electroweak Symmetry Breaking from Theory Space
Recently, a new class of realistic models for electroweak symmetry breaking
have been constructed, without supersymmetry. These theories have naturally
light Higgs bosons and perturbative new physics at the TeV scale. We describe
these models in detail, and show that electroweak symmetry breaking can be
triggered by a large top quark Yukawa coupling. A rich spectrum of particles is
predicted, with a pair of light Higgs doublets accompanied by new light weak
triplet and singlet scalars. The lightest of these new scalars is charged under
a geometric discrete symmetry and is therefore stable, providing a new
candidate for WIMP dark matter. At TeV energies, a plethora of new heavy
scalars, gauge bosons and fermions are revealed, with distinctive quantum
numbers and decay modes.Comment: 22 pages, latex, 6 figures. Numerical results corrected,
clarifications added, conclusions unchange
Shape of Deconstruction
We construct a six-dimensional Maxwell theory using a latticized extra space,
the continuum limit of which is a shifted torus recently discussed by Dienes.
This toy model exhibits the correspondence between continuum theory and
discrete theory, and give a geometrical insight to theory-space model building.Comment: 10 pages, 2 figures, RevTeX4. a citation adde
What Precision Electroweak Physics Says About the SU(6)/Sp(6) Little Higgs
We study precision electroweak constraints on the close cousin of the
Littlest Higgs, the SU(6)/Sp(6) model. We identify a near-oblique limit in
which the heavy W' and B' decouple from the light fermions, and then calculate
oblique corrections, including one-loop contributions from the extended top
sector and the two Higgs doublets. We find regions of parameter space that give
acceptably small precision electroweak corrections and only mild fine tuning in
the Higgs potential, and also find that the mass of the lightest Higgs boson is
relatively unconstrained by precision electroweak data. The fermions from the
extended top sector can be as light as 1 TeV, and the W' can be as light as 1.8
TeV. We include an independent breaking scale for the B', which can still have
a mass as low as a few hundred GeV.Comment: 52 pages, 16 figure
A "Littlest Higgs" Model with Custodial SU(2) Symmetry
In this note, a ``littlest higgs'' model is presented which has an
approximate custodial SU(2) symmetry. The model is based on the coset space
. The light pseudo-goldstone bosons of the theory
include a {\it single} higgs doublet below a TeV and a set of three
triplets and an electroweak singlet in the TeV range. All of these scalars
obtain approximately custodial SU(2) preserving vacuum expectation values. This
model addresses a defect in the earlier moose
model, with the only extra complication being an extended top sector. Some of
the precision electroweak observables are computed and do not deviate
appreciably from Standard Model predictions. In an S-T oblique analysis, the
dominant non-Standard Model contributions are the extended top sector and higgs
doublet contributions. In conclusion, a wide range of higgs masses is allowed
in a large region of parameter space consistent with naturalness, where large
higgs masses requires some mild custodial SU(2) violation from the extended top
sector.Comment: 22 pages + 8 figures; JHEP style, added references and extra
discussion on size of T contributions, as well as some other minor
clarifications. Version to appear in JHE
Vacuum Stability in Split Susy and Little Higgs Models
We study the stability of the effective higgs potential in the split
supersymmetry and Little Higgs models. In particular, we study the effects of
higher dimensional operators in the effective potential on the higgs mass
predictions. We find that the size and sign of the higher dimensional operators
can significantly change the higgs mass required to maintain vacuum stability
in Split Susy models. In the Little Higgs models the effects of higher
dimensional operators can be large because of a relatively lower cut-off scale.
Working with a specific model we find that a contribution from the higher
dimensional operator with coefficient of O(1) can destabilize the vacuum.Comment: Latex 22 pages, 3 figures. Added discussion, published versio
Little Hierarchy, Little Higgses, and a Little Symmetry
Little Higgs theories are an attempt to address the little hierarchy problem,
i.e., the tension between the naturalness of the electroweak scale and the
precision measurements showing no evidence for new physics up to 5-10 TeV. In
little Higgs theories, the Higgs mass-squareds are protected to the one-loop
order from the quadratic divergence. This allows the cutoff to be raised up to
\~10 TeV, beyond the scales probed by the precision data. However, strong
constraints can still arise from the contributions of the new TeV scale
particles and hence re-introduces the fine-tuning problem. In this paper we
show that a new symmetry, denoted as T-parity, under which all heavy gauge
bosons and scalar triplets are odd, can remove all the tree-level contributions
to the electroweak observables and therefore makes the little Higgs theories
completely natural. The T-parity can be manifestly implemented in a majority of
little Higgs models by following the most general construction of the low
energy effective theory a la Callan, Coleman, Wess and Zumino. In particular,
we discuss in detail how to implement the T-parity in the littlest Higgs model
based on SU(5)/SO(5). The symmetry breaking scale f can be even lower than 500
GeV if the contributions from the unknown UV physics at the cutoff are somewhat
small. The existence of -parity has drastic impacts on the phenomenology of
the little Higgs theories. The T-odd particles need to be pair-produced and
will cascade down to the lightest T-odd particle (LTP) which is stable. A
neutral LTP gives rise to missing energy signals at the colliders which can
mimic supersymmetry. It can also serve as a good dark matter candidate.Comment: 20 pages, 2 figures, RevTeX; v2: Yukawa sector in the SU(5)/SO(5)
model slightly modified. Also added comments on the Dirac mass term for the
fermionic doublet partner; v3: clarifying comments on the modified Yukawa
sector. version to appear on JHE
Higher dimensional supersymmetry in 4D superspace
We present an explicit formulation of supersymmetric Yang-Mills theories from
\D= 5 to 10 dimensions in the familiar \N=1,\D=4 superspace. This provides
the rules for globally supersymmetric model building with extra dimensions and
in particular allows us to simply write down SUSY preserving
interactions between bulk fields and fields localized on branes. We present a
few applications of the formalism by way of illustration, including
supersymmetric ``shining'' of bulk fields, orbifolds and localization of chiral
fermions, anomaly inflow and super-Chern-Simons theories.Comment: Typos corrected. Added reference to early work by Marcus, Sagnotti
and Siegel and a term to the non-Abelian Lagrangian for D>5 formally needed
for gauge invariance. The results however remain unchange
Precision Electroweak Observables in the Minimal Moose Little Higgs Model
Little Higgs theories, in which the Higgs particle is realized as the
pseudo-Goldstone boson of an approximate global chiral symmetry have generated
much interest as possible alternatives to weak scale supersymmetry. In this
paper we analyze precision electroweak observables in the Minimal Moose model
and find that in order to be consistent with current experimental bounds, the
gauge structure of this theory needs to be modified. We then look for viable
regions of parameter space in the modified theory by calculating the various
contributions to the S and T parameters.Comment: v2: 17 pages, 9 figures. Typeset in JHEP style. Added a references
and two figures showing parameter space for each of two reference points.
Corrected typo
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