427 research outputs found
Collective Quartics from Simple Groups
This article classifies Little Higgs models that have collective quartic
couplings. There are two classes of collective quartics: Special Cosets and
Special Quartics. After taking into account dangerous singlets, the smallest
Special Coset models are SU(5)/SO(5) and SU(6)/Sp(6). The smallest Special
Quartic model is SU(5)/SU(3) x SU(2) x U(1) and has not previously been
considered as a candidate Little Higgs model.Comment: 22 pages, 2 figure
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
Probing Slepton Mass Non-Universality at e^+e^- Linear Colliders
There are many models with non-universal soft SUSY breaking sfermion mass
parameters at the grand unification scale. Even in the mSUGRA model scalar mass
unification might occur at a scale closer to M_Planck, and renormalization
effects would cause a mass splitting at M_GUT. We identify an experimentally
measurable quantity Delta that correlates strongly with delta m^2 =
m^2_{selectron_R}(M_GUT) - m^2_{selectron_L}(M_GUT), and which can be measured
at electron-positron colliders provided both selectrons and the chargino are
kinematically accessible. We show that if these sparticle masses can be
measured with a precision of 1% at a 500 GeV linear collider, the resulting
precision in the determination of Delta may allow experiments to distinguish
between scalar mass unification at the GUT scale from the corresponding
unification at Q ~ M_Planck. Experimental determination of Delta would also
provide a distinction between the mSUGRA model and the recently proposed
gaugino-mediation model. Moreover, a measurement of Delta (or a related
quantity Delta') would allow for a direct determination of delta m^2.Comment: 15 pages, RevTeX, 4 postscript figure
Near-brane SU(6) origin Higgs in Scherk-Schwarz breaking of five-dimensional SU(6) GUT
The symmetry breaking of five-dimensional SU(6) GUT is realized by
Scherk-Schwarz mechanisms through trivial and pseudo nontrivial orbifold S1/Z2
breakings to produce dimensional deconstruction 5D SU(6) \rightarrow4D SU(6).
The latter also induces near-brane weakly-coupled SU(6) Baby Higgs to further
break the symmetry into SU(3)C \otimes SU(3)H \otimes U(1)C. The model
successfully provides a scenario of the origin of (Little) Higgs from GUT
scale, produces the (intermediate and light) Higgs boson with the most
preferred range and establishes coupling unification and compactification scale
correctly.Comment: 23 pages, 5 figure
Supersymmetry and the Anomalous Anomalous Magnetic Moment of the Muon
The recently reported measurement of the muon's anomalous magnetic moment
differs from the standard model prediction by 2.6 standard deviations. We
examine the implications of this discrepancy for supersymmetry. Deviations of
the reported magnitude are generic in supersymmetric theories. Based on the new
result, we derive model-independent upper bounds on the masses of observable
supersymmetric particles. We also examine several model frameworks. The sign of
the reported deviation is as predicted in many simple models, but disfavors
anomaly-mediated supersymmetry breaking.Comment: 4 pages, 4 figures, version to appear in Phys. Rev. Let
Sneutrino Mass Measurements at e+e- Linear Colliders
It is generally accepted that experiments at an e+e- linear colliders will be
able to extract the masses of the selectron as well as the associated
sneutrinos with a precision of ~ 1% by determining the kinematic end points of
the energy spectrum of daughter electrons produced in their two body decays to
a lighter neutralino or chargino. Recently, it has been suggested that by
studying the energy dependence of the cross section near the production
threshold, this precision can be improved by an order of magnitude, assuming an
integrated luminosity of 100 fb^-1. It is further suggested that these
threshold scans also allow the masses of even the heavier second and third
generation sleptons and sneutrinos to be determined to better than 0.5%. We
re-examine the prospects for determining sneutrino masses. We find that the
cross sections for the second and third generation sneutrinos are too small for
a threshold scan to be useful. An additional complication arises because the
cross section for sneutrino pair to decay into any visible final state(s)
necessarily depends on an unknown branching fraction, so that the overall
normalization in unknown. This reduces the precision with which the sneutrino
mass can be extracted. We propose a different strategy to optimize the
extraction of m(\tilde{\nu}_\mu) and m(\tilde{\nu}_\tau) via the energy
dependence of the cross section. We find that even with an integrated
luminosity of 500 fb^-1, these can be determined with a precision no better
than several percent at the 90% CL. We also examine the measurement of
m(\tilde{\nu}_e) and show that it can be extracted with a precision of about
0.5% (0.2%) with an integrated luminosity of 120 fb^-1 (500 fb^-1).Comment: RevTex, 46 pages, 15 eps figure
The Little Higgs from a Simple Group
We present a model of electroweak symmetry breaking in which the Higgs boson
is a pseudo-Nambu-Goldstone boson. By embedding the standard model SU(2) x U(1)
into an SU(4) x U(1) gauge group, one-loop quadratic divergences to the Higgs
mass from gauge and top loops are canceled automatically with the minimal
particle content. The potential contains a Higgs quartic coupling which does
not introduce one-loop quadratic divergences. Our theory is weakly coupled at
the electroweak scale, it has new weakly coupled particles at the TeV scale and
a cutoff above 10 TeV, all without fine tuning. We discuss the spectrum of the
model and estimate the constraints from electroweak precision measurements.Comment: 29 pages, referencing error corrected after death threats, dude
remove
Solitons in Supersymmety Breaking Meta-Stable Vacua
In recently found supersymmetry-breaking meta-stable vacua of the
supersymmetric QCD, we examine possible exsitence of solitons. Homotopy groups
of the moduli space of the meta-stable vacua show that there is no nontrivial
soliton for SU(N_c) gauge group. When U(1)_B symmetry present in the theory is
gauged, we find non-BPS solitonic (vortex) strings whose existence and
properties are predicted from brane configurations. We obtain explicit
classical solutions which reproduce the predicitions. For SO(N_c) gauge group,
we find there are solitonic strings for N = N_f-N_c+4 = 2, and Z_2 strings for
the other N. The strings are meta-stable as they live in the meta-stable vacua.Comment: 30 pages, 14 figures, Comments on stability of non-BPS vortices are
added, Comments on sigma model solitons are added, An appendix is adde
Neutrino physics at large colliders
Large colliders are not sensitive to light neutrino masses and character, but
they can produce new heavy neutrinos, allowing also for the determination of
their Dirac or Majorana nature. We review the discovery limits at the next
generation of large colliders.Comment: LaTeX 32 pages. This review summarises and extends work presented at
several conferences. To appear in the proceedings of CORFU2005. References
adde
Unitarity in Dirichlet Higgs Model
We show that a five dimensional Universal Extra Dimension model, compactified
on a line segment, is consistently formulated even when the gauge symmetry is
broken solely by non-zero Dirichlet boundary conditions on a bulk Higgs field,
without any quartic interaction. We find that the longitudinal W+W- elastic
scattering amplitude, under the absence of the Higgs zero-mode, is unitarized
by exchange of infinite towers of KK Higgs bosons. Resultant amplitude scales
linearly with the scattering energy, exhibiting five dimensional nature. A
tree-level partial-wave unitarity condition is satisfied up to 6.7 (5.7) TeV
for the KK scale 430 (500) GeV, favored by the electroweak data within 90% CL.Comment: 14pages, 2 figures (v1); References added (v2); Trivial error
corrected: u -> t and \cos\theta -> -\cos\theta, references added (v3);
comments added, a reference added, version to appear in Eur. Phys. J. C (v4);
Expressions matched to EPJC style, obsolete affiliation (on leave) has been
removed (v5
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