25 research outputs found
The Supersymmetric Higgs
In the Minimal Supersymmetric Standard Model (the MSSM), the electroweak
symmetry is restored as supersymmetry-breaking terms are turned off. We
describe a generic extension of the MSSM where the electroweak symmetry is
broken in the supersymmetric limit. We call this limit the "sEWSB" phase, short
for supersymmetric electroweak symmetry breaking. We define this phase in an
effective field theory that only contains the MSSM degrees of freedom. The
sEWSB vacua naturally have an inverted scalar spectrum, where the heaviest
CP-even Higgs state has Standard Model-like couplings to the massive vector
bosons; experimental constraints in the scalar Higgs sector are more easily
satisfied than in the MSSM.Comment: 34 pages, 5 figure
BMSSM Higgs Bosons at the Tevatron and the LHC
We study extensions of the Minimal Supersymmetric Standard Model (MSSM) with
new degrees of freedom that couple sizably to the MSSM Higgs sector and lie in
the TeV range. After integrating out the physics at the TeV scale, the
resulting Higgs spectrum can significantly differ from typical supersymmetric
scenarios, thereby providing a window Beyond the MSSM (BMSSM). Taking into
account current LEP and Tevatron constraints, we perform an in-depth analysis
of the Higgs collider phenomenology and explore distinctive characteristics of
our scenario with respect to both the Standard Model and the MSSM.
We propose benchmark scenarios to illustrate specific features of BMSSM Higgs
searches at the Tevatron and the LHC.Comment: 18 pages, 9 figures; added parameters for each benchmark point, typos
corrected, final version published by Phys. Rev.
Electroweak Phase Transition, Higgs Diphoton Rate, and New Heavy Fermions
We show that weak scale vector-like fermions with order one couplings to the
Higgs can lead to a novel mechanism for a strongly first-order electroweak
phase transition (EWPhT), through their tendency to drive the Higgs quartic
coupling negative. These same fermions could also enhance the loop-induced
branching fraction of the Higgs into two photons, as suggested by the recent
discovery of a ~125 GeV Higgs-like state at the CERN Large Hadron Collider
(LHC). Our results suggest that measurements of the diphoton decay rate of the
Higgs and its self coupling, at the LHC or perhaps at a future lepton collider,
could probe the EWPhT in the early Universe, with significant implications for
the viability of electroweak baryogenesis scenarios.Comment: 6 pages, 1 figure. Revised version shows that the original
conclusions hold in a distinct region of parameter space. New discussion on
collider probes adde
TASI 2011: Four Lectures on TeV Scale Extra Dimensions
Compact spatial dimension at the TeV scale remain an intriguing possibility
that is currently being tested at the LHC. We give an introductory review of
extra-dimensional models and ideas, from a phenomenological perspective, but
emphasizing the appropriate theoretical tools. We emphasize the power and
limitations of such constructions, and give a self-contained account of the
methods necessary to understand the associated physics. We also review a number
of examples that illustrate how extra-dimensional ideas can shed light on open
questions in the Standard Model. An introduction to holography is provided.
These are the notes of my TASI 2011 Lectures on Extra Dimensions.Comment: 79 pages, 15 figure
Minimal Composite Higgs Models at the LHC
We consider composite Higgs models where the Higgs is a pseudo-Nambu
Goldstone boson arising from the spontaneous breaking of an approximate global
symmetry by some underlying strong dynamics. We focus on the SO(5) -> SO(4)
symmetry breaking pattern, assuming the partial compositeness paradigm. We
study the consequences on Higgs physics of the fermionic representations
produced by the strong dynamics, that mix with the Standard Model (SM) degrees
of freedom. We consider models based on the lowest-dimensional representations
of SO(5) that allow for the custodial protection of the Z -> b b coupling, i.e.
the 5, 10 and 14. We find a generic suppression of the gluon fusion process,
while the Higgs branching fractions can be enhanced or suppressed compared to
the SM. Interestingly, a precise measurement of the Higgs boson couplings can
distinguish between different realizations in the fermionic sector, thus
providing crucial information about the nature of the UV dynamics.Comment: 55 pages, 18 figures, References adde
The Dynamical Composite Higgs
We present a simple microscopic realization of a pseudo-Nambu-Goldstone
(pNGB) boson Higgs scenario arising from the breaking of . The Higgs constituents are explicitly identified as well as the
interactions responsible for forming the bound state and breaking the
electroweak symmetry. This outcome follows from the presence of four-fermion
interactions with a super-critical coupling, and uses the Nambu-Jona-Lasinio
mechanism to break the global symmetry. The Higgs potential is found to
be insensitive to high energy scales due to the existence of an approximate
infrared fixed point. The appearance of vector resonances is described and the
correspondence with other proposals in the literature established. The model
described here is significantly simpler than other recent ultraviolet
completions of pNGB scenarios. The observed Higgs mass can be accommodated, and
agreement with electroweak precision tests achieved in certain regions of
parameter space. There are also new vector-like fermions, some of which may lie
within reach of the LHC. In addition, we predict a heavy standard model singlet
scalar in the multi-TeV range. The amount of fine-tuning required in the model
is studied. Finally, we show that such a scheme can be completed in the
ultraviolet by a renormalizable theory.Comment: 32 pages plus appendices, 7 figures - reference adde
Calculable Dynamical Supersymmetry Breaking on Deformed Moduli Spaces
We consider models of dynamical supersymmetry breaking in which the
extremization of a tree-level superpotential conflicts with a quantum
constraint. We show that in such models the low-energy effective theory near
the origin of moduli space is an O'Raifeartaigh model, and the sign of the
mass-squared for the pseudo-flat direction at the origin is calculable. We
analyze vector-like models with gauge groups SU(N) and Sp(2N) with and without
global symmetries. In all cases there is a stable minimum at the origin with an
unbroken U(1)_R symmetry.Comment: 8 pages, LaTeX2e, no figure
A Critical Cosmological Constant from Millimeter Extra Dimensions
We consider `brane universe' scenarios with standard-model fields localized
on a 3-brane in 6 spacetime dimensions. We show that if the spacetime is
rotationally symmetric about the brane, local quantities in the bulk are
insensitive to the couplings on the brane. This potentially allows
compactifications where the effective 4-dimensional cosmological constant is
independent of the couplings on the 3-brane. We consider several possible
singularity-free compactification mechanisms, and find that they do not
maintain this property. We also find solutions with naked spacetime
singularities, and we speculate that new short-distance physics can become
important near the singularities and allow a compactification with the desired
properties. The picture that emerges is that standard-model loop contributions
to the effective 4-dimensional cosmological constant can be cut off at
distances shorter than the compactification scale. At shorter distance scales,
renormalization effects due to standard-model fields renormalize the 3-brane
tension, which changes a deficit angle in the transverse space without
affecting local quantities in the bulk. For a compactification scale of order
10^{-2} mm, this gives a standard-model contribution to the cosmological
constant in the range favored by cosmology.Comment: 15 pages, LaTeX2e. Major revisions; see abstrac
Realistic Anomaly-mediated Supersymmetry Breaking
We consider supersymmetry breaking communicated entirely by the
superconformal anomaly in supergravity. This scenario is naturally realized if
supersymmetry is broken in a hidden sector whose couplings to the observable
sector are suppressed by more than powers of the Planck scale, as occurs if
supersymmetry is broken in a parallel universe living in extra dimensions. This
scenario is extremely predictive: soft supersymmetry breaking couplings are
completely determined by anomalous dimensions in the effective theory at the
weak scale. Gaugino and scalar masses are naturally of the same order, and
flavor-changing neutral currents are automatically suppressed. The most glaring
problem with this scenario is that slepton masses are negative in the minimal
supersymmetric standard model. We point out that this problem can be simply
solved by coupling extra Higgs doublets to the leptons. Lepton flavor-changing
neutral currents can be naturally avoided by approximate symmetries. We also
describe more speculative solutions involving compositeness near the weak
scale. We then turn to electroweak symmetry breaking. Adding an explicit \mu
term gives a value for B\mu that is too large by a factor of order 100. We
construct a realistic model in which the \mu term arises from the vacuum
expectation value of a singlet field, so all weak-scale masses are directly
related to m_{3/2}. We show that fully realistic electroweak symmetry breaking
can occur in this model with moderate fine-tuning.Comment: 32 pages, LaTeX2e, 3 eps figure