662 research outputs found
Heavy superpartners with less tuning from hidden sector renormalisation
In supersymmetric extensions of the Standard Model, superpartner masses
consistent with collider bounds typically introduce significant tuning of the
electroweak scale. We show that hidden sector renormalisation can greatly
reduce such a tuning if the supersymmetry breaking, or mediating, sector runs
through a region of strong coupling not far from the weak scale. In the
simplest models, only the tuning due to the gaugino masses is improved, and a
weak scale gluino mass in the region of 5 TeV may be obtained with an
associated tuning of only one part in ten. In models with more complex
couplings between the visible and hidden sectors, the tuning with respect to
sfermions can also be reduced. We give an example of a model, with low scale
gauge mediation and superpartner masses allowed by current LHC bounds, that has
an overall tuning of one part in twenty.Comment: 18 pages, 6 figure
Electroweak relaxation from finite temperature
We study theories which naturally select a vacuum with parametrically small
Electroweak Scale due to finite temperature effects in the early universe. In
particular, there is a scalar with an approximate shift symmetry broken by a
technically natural small coupling to the Higgs, and a temperature dependent
potential. As the temperature of the universe drops, the scalar follows the
minimum of its potential altering the Higgs mass squared parameter. The scalar
also has a periodic potential with amplitude proportional to the Higgs
expectation value, which traps it in a vacuum with a small Electroweak Scale.
The required temperature dependence of the potential can occur through strong
coupling effects in a hidden sector that are suppressed at high temperatures.
Alternatively, it can be generated perturbatively from a one-loop thermal
potential. In both cases, for the scalar to be displaced, a hidden sector must
be reheated to temperatures significantly higher than the visible sector.
However this does not violate observational constraints provided the hidden
sector energy density is transferred to the visible sector without disrupting
big bang nucleosynthesis. We also study how the mechanism can be implemented
when the visible sector is completed to the Minimal Supersymmetric Standard
Model at a high scale. Models with a UV cutoff of 10 TeV and no fields taking
values over a range greater than 10^12 GeV are possible, although the scalar
must have a range of order 10^8 times the effective decay constant in the
periodic part of its potential.Comment: 17 pages, 1 figure, JHEP versio
Retrofitted Natural Supersymmetry from a U(1)
We propose that a single, spontaneously broken, U(1) gauge symmetry may be
responsible for suppressing both the first two generation Yukawa couplings, and
also, in a correlated manner, parameters in the dynamical supersymmetry (SUSY)
breaking sector by the mechanism of retrofitting. In the dynamical SUSY
breaking sector, these small parameters are typically required in order to
introduce R-symmetry breaking in a controlled manner and obtain
phenomenologically viable meta-stable vacua. The heavy U(1) multiplet mediates
a dominant contribution to the first two generation MSSM sfermion soft masses,
while gauge mediation provides a parametrically suppressed soft term
contribution to the stop and most other states, so realising a natural SUSY
spectrum in a fashion consistent with SUSY unification. In explicit models the
spectra obtained can be such that current LHC limits are evaded, and
predictions of flavour changing processes are consistent with observation. We
examine both implementations with low scale mediation, and string-motivated
examples where the U(1) is anomalous before the inclusion of a generalised
Green-Schwarz mechanism.Comment: V2: References adde
Annihilation Signals from Asymmetric Dark Matter
In the simplest models of asymmetric dark matter (ADM) annihilation signals
are not expected, since the DM is non-self-conjugate and the relic density of
anti-DM is negligible. We investigate a new class of models in which a
symmetric DM component, in the `low-mass' 1-10 GeV regime favoured for linking
the DM and baryon asymmetries, is repopulated through decays. We find that, in
models without significant velocity dependence of the annihilation cross
section, observational constraints generally force these decays to be
(cosmologically) slow. These late decays can give rise to gamma-ray signal
morphologies differing from usual annihilation profiles. A distinctive feature
of such models is that signals may be absent from dwarf spheroidal galaxies.Comment: 31 pages, 9 figures, v3; minor corrections, and reference added -
matches version published in JHE
Searching for Fermi Surfaces in Super-QED
The exploration of strongly-interacting finite-density states of matter has
been a major recent application of gauge-gravity duality. When the theories
involved have a known Lagrangian description, they are typically deformations
of large supersymmetric gauge theories, which are unusual from a
condensed-matter point of view. In order to better interpret the
strong-coupling results from holography, an understanding of the weak-coupling
behavior of such gauge theories would be useful for comparison. We take a first
step in this direction by studying several simple supersymmetric and
non-supersymmetric toy model gauge theories at zero temperature. Our
supersymmetric examples are super-QED and
super-QED, with finite densities of electron number and R-charge respectively.
Despite the fact that fermionic fields couple to the chemical potentials we
introduce, the structure of the interaction terms is such that in both of the
supersymmetric cases the fermions do not develop a Fermi surface. One might
suspect that all of the charge in such theories would be stored in the scalar
condensates, but we show that this is not necessarily the case by giving an
example of a theory without a Fermi surface where the fermions still manage to
contribute to the charge density.Comment: 37 pages, 3 figures. V3: minor clarifications added, version to
appear in JHE
Axion Mediation
We explore the possibility that supersymmetry breaking is mediated to the
Standard Model sector through the interactions of a generalized axion multiplet
that gains a F-term expectation value. Using an effective field theory
framework we enumerate the most general possible set of axion couplings and
compute the Standard Model sector soft-supersymmetry-breaking terms. Unusual,
non-minimal spectra, such as those of both natural and split supersymmetry are
easily implemented. We discuss example models and low-energy spectra, as well
as implications of the particularly minimal case of mediation via the QCD axion
multiplet. We argue that if the Peccei-Quinn solution to the strong-CP problem
is realized in string theory then such axion-mediation is generic, while in a
field theory model it is a natural possibility in both DFSZ- and KSVZ-like
regimes. Axion mediation can parametrically dominate gravity-mediation and is
also cosmologically beneficial as the constraints arising from axino and
gravitino overproduction are reduced. Finally, in the string context, axion
mediation provides a motivated mechanism where the UV completion naturally
ameliorates the supersymmetric flavor problem.Comment: 32 pages, 3 figures, references added, minor change
Alien Registration- Hardy, Edward (Sanford, York County)
https://digitalmaine.com/alien_docs/3428/thumbnail.jp
The Heterotic Superpotential and Moduli
We study the four-dimensional effective theory arising from ten-dimensional
heterotic supergravity compactified on manifolds with torsion. In particular,
given the heterotic superpotential appropriately corrected at
to account for the Green-Schwarz anomaly cancellation
mechanism, we investigate properties of four-dimensional Minkowski vacua of
this theory. Considering the restrictions arising from F-terms and D-terms we
identify the infinitesimal massless moduli space of the theory. We show that it
agrees with the results that have recently been obtained from a ten-dimensional
perspective where supersymmetric Minkowski solutions including the Bianchi
identity correspond to an integrable holomorphic structure, with infinitesimal
moduli calculated by its first cohomology. As has recently been noted,
interplay of complex structure and bundle deformations through holomorphic and
anomaly constraints can lead to fewer moduli than may have been expected. We
derive a relation between the number of complex structure and bundle moduli
removed from the low energy theory in this way, and give conditions for there
to be no complex structure moduli or bundle moduli remaining in the low energy
theory. The link between Yukawa couplings and obstruction theory is also
briefly discussed.Comment: 35 pages, minor correction
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