1,043 research outputs found
Strongly Coupled Semi-Direct Mediation of Supersymmetry Breaking
Strongly coupled semi-direct gauge mediation models of supersymmetry breaking
through massive mediators with standard model charges are investigated by means
of composite degrees of freedom. Sizable mediation is realized to generate the
standard model gaugino masses for a small mediator mass without breaking the
standard model symmetries.Comment: 7 pages; v2: the model generalized, gaugino mass corrected; v3:
explanations expanded, references adde
Moduli Space of Global Symmetry in N=1 Supersymmetric Theories and the Quasi-Nambu-Goldstone Bosons
We derive the moduli space for the global symmetry in N=1 supersymmetric
theories. We show, at the generic points, it coincides with the space of
quasi-Nambu-Goldstone (QNG) bosons, which appear besides the ordinary
Nambu-Goldstone (NG) bosons when global symmetry G breaks down spontaneously to
its subgroup H with preserving N=1 supersymmetry. At the singular points, most
of the NG bosons change to the QNG bosons and the unbroken global symmetry is
enhanced. The G-orbits parametrized by the NG bosons are the fibre at the
moduli space and the singular points correspond to the point where H-orbit (in
G-orbit) shrinks. We also show the low-energy effective Lagrangian is the
arbitrary function of the orbit map.Comment: LaTex, 42 pages, 8 figures, final version to appear in
Int.J.Mod.Phys.
Mediation of supersymmetry breaking in extra dimensions
We review the mechanisms of supersymmetry breaking mediation that occur in
sequestered models, where the visible and the hidden sectors are separated by
an extra dimension and communicate only via gravitational interactions. By
locality, soft breaking terms are forbidden at the classical level and reliably
computable within an effective field theory approach at the quantum level. We
present a self-contained discussion of these radiative gravitational effects
and the resulting pattern of soft masses, and give an overview of realistic
model building based on this set-up. We consider both flat and warped extra
dimensions, as well as the possibility that there be localized kinetic terms
for the gravitational fields.Comment: LaTex, 15 pages; brief review prepared for MPLA. v2: minor
correction
Supersymmetry-Breaking Loops from Analytic Continuation into Superspace
We extend to all orders in perturbation theory a method to calculate
supersymmetry-breaking effects by analytic continuation of the renormalization
group into superspace. A central observation is that the renormalized gauge
coupling can be extended to a real vector superfield, thereby including soft
breaking effects in the gauge sector. We explain the relation between this
vector superfield coupling and the "holomorphic" gauge coupling, which is a
chiral superfield running only at 1 loop. We consider these issues for a number
of regulators, including dimensional reduction. With this method, the
renormalization group equations for soft supersymmetry breaking terms are
directly related to supersymmetric beta functions and anomalous dimensions to
all orders in perturbation theory. However, the real power of the formalism
lies in computing finite soft breaking effects corresponding to high-loop
component calculations. We prove that the gaugino mass in gauge-mediated
supersymmetry breaking is ``screened'' from strong interactions in the
messenger sector. We present the complete next-to-leading calculation of
gaugino masses (2 loops) and sfermion masses (3 loops) in minimal gauge
mediation, and several other calculations of phenomenological relevance.Comment: 50 pages, 1 ps and 1 eps figure, LaTe
Cosmological Simulations of Normal-Branch Braneworld Gravity
We introduce a cosmological model based on the normal branch of DGP
braneworld gravity with a smooth dark energy component on the brane. The
expansion history in this model is identical to LambdaCDM, thus evading all
geometric constraints on the DGP cross-over scale r_c. This model can serve as
a first approximation to more general braneworld models whose cosmological
solutions have not been obtained yet. We study the formation of large scale
structure in this model in the linear and non-linear regime using N-body
simulations for different values of r_c. The simulations use the code presented
in (F.S., arXiv:0905.0858) and solve the full non-linear equation for the
brane-bending mode in conjunction with the usual gravitational dynamics. The
brane-bending mode is attractive rather than repulsive in the DGP normal
branch, hence the sign of the modified gravity effects is reversed compared to
those presented in arXiv:0905.0858. We compare the simulation results with
those of ordinary LambdaCDM simulations run using the same code and initial
conditions. We find that the matter power spectrum in this model shows a
characteristic enhancement peaking at k ~ 0.7 h/Mpc. We also find that the
abundance of massive halos is significantly enhanced. Other results presented
here include the density profiles of dark matter halos, and signatures of the
brane-bending mode self-interactions (Vainshtein mechanism) in the simulations.
Independently of the expansion history, these results can be used to place
constraints on the DGP model and future generalizations through their effects
on the growth of cosmological structure.Comment: 17 pages, 10 figures; v2: minor changes; v3: references added; v4:
added appendix on comparison with previous results; matches published
version; v5: corrected Eqs. (2.4-2.5) and Fig. 1 following Ref. [28]; all
following results unchange
Self-Consistent Cosmological Simulations of DGP Braneworld Gravity
We perform cosmological N-body simulations of the Dvali-Gabadadze-Porrati
braneworld model, by solving the full non-linear equations of motion for the
scalar degree of freedom in this model, the brane bending mode. While coupling
universally to matter, the brane-bending mode has self-interactions that become
important as soon as the density field becomes non-linear. These
self-interactions lead to a suppression of the field in high-density
environments, and restore gravity to General Relativity. The code uses a
multi-grid relaxation scheme to solve the non-linear field equation in the
quasi-static approximation. We perform simulations of a flat self-accelerating
DGP model without cosmological constant. The results of the DGP simulations are
compared with standard gravity simulations assuming the same expansion history,
and with DGP simulations using the linearized equation for the brane bending
mode. This allows us to isolate the effects of the non-linear self-couplings of
the field which are noticeable already on quasi-linear scales. We present
results on the matter power spectrum and the halo mass function, and discuss
the behavior of the brane bending mode within cosmological structure formation.
We find that, independently of CMB constraints, the self-accelerating DGP model
is strongly constrained by current weak lensing and cluster abundance
measurements.Comment: 21 pages; 10 figures. Revised version matching published versio
Metastable gravity on classical defects
We discuss the realization of metastable gravity on classical defects in
infinite-volume extra dimensions. In dilatonic Einstein gravity, it is found
that the existence of metastable gravity on the defect core requires violation
of the Dominant Energy Condition for codimension Nc = 2 defects. This is
illustrated with a detailed analysis of a six-dimensional hyperstring minimally
coupled to dilaton gravity. We present the general conditions under which a
codimension Nc > 2 defect admits metastable modes, and find that they differ
from lower codimensional models in that, under certain conditions, they do not
require violation of energy conditions to support quasi-localized gravity.Comment: 10 pages, 3 figures, uses RevTeX, typos corrected, matches published
versio
Anomaly Mediated Supersymmetry Breaking in Four Dimensions, Naturally
We present a simple four-dimensional model in which anomaly mediated
supersymmetry breaking naturally dominates. The central ingredient is that the
hidden sector is near a strongly-coupled infrared fixed-point for several
decades of energy below the Planck scale. Strong renormalization effects then
sequester the hidden sector from the visible sector. Supersymmetry is broken
dynamically and requires no small input parameters. The model provides a
natural and economical explanation of the hierarchy between the
supersymmetry-breaking scale and the Planck scale, while allowing anomaly
mediation to address the phenomenological challenges posed by weak scale
supersymmetry. In particular, flavor-changing neutral currents are naturally
near their experimental limits.Comment: 14 pages, Late
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