605 research outputs found
Exponential Hierarchies from Anderson Localization in Theory Space
We present a new mechanism for generating exponential hierarchies in
four-dimensional field theories inspired by Anderson localization in one
dimension, exploiting an analogy between the localization of electron energy
eigenstates along a one-dimensional disordered wire and the localization of
mass eigenstates along a local "theory space" with random mass parameters. Mass
eigenstates are localized even at arbitrarily weak disorder, with exponentially
suppressed couplings to sites in the theory space. The mechanism is quite
general and may be used to exponentially localize fields of any spin. We apply
the localization mechanism to two hierarchies in Standard Model parameters ---
the smallness of neutrino masses and the ordering of quark masses --- and
comment on possible relevance to the electroweak hierarchy problem. This raises
the compelling possibility that some of the large hierarchies observed in and
beyond the Standard Model may result from disorder, rather than order.Comment: 5 pages and 1 figur
Testing Split Supersymmetry with Inflation
Split supersymmetry (SUSY) -- in which SUSY is relevant to our universe but
largely inaccessible at current accelerators -- has become increasingly
plausible given the absence of new physics at the LHC, the success of gauge
coupling unification, and the observed Higgs mass. Indirect probes of split
SUSY such as electric dipole moments (EDMs) and flavor violation offer hope for
further evidence but are ultimately limited in their reach. Inflation offers an
alternate window into SUSY through the direct production of superpartners
during inflation. These particles are capable of leaving imprints in future
cosmological probes of primordial non-gaussianity. Given the recent
observations of BICEP2, the scale of inflation is likely high enough to probe
the full range of split SUSY scenarios and therefore offers a unique advantage
over low energy probes. The key observable for future experiments is
equilateral non-gaussianity, which will be probed by both cosmic microwave
background (CMB) and large scale structure (LSS) surveys. In the event of a
detection, we forecast our ability to find evidence for superpartners through
the scaling behavior in the squeezed limit of the bispectrum.Comment: 19 pages, 6 figure
The Fraternal WIMP Miracle
We identify and analyze thermal dark matter candidates in the fraternal twin
Higgs model and its generalizations. The relic abundance of fraternal twin dark
matter is set by twin weak interactions, with a scale tightly tied to the weak
scale of the Standard Model by naturalness considerations. As such, the dark
matter candidates benefit from a "fraternal WIMP miracle," reproducing the
observed dark matter abundance for dark matter masses between 50 and 150 GeV.
However, the couplings dominantly responsible for dark matter annihilation do
not lead to interactions with the visible sector. The direct detection rate is
instead set via fermionic Higgs portal interactions, which are likewise
constrained by naturalness considerations but parametrically weaker than those
leading to dark matter annihilation. The predicted direct detection cross
section is close to current LUX bounds and presents an opportunity for the next
generation of direct detection experiments.Comment: 22 pages, 6 figures. v2: Relic abundance calculations revised and
improved, citations added. Conclusions largely unchanged. v3: Minor changes,
accepted by JCA
Scherk-Schwarz Supersymmetry Breaking in 4D
Using the techniques of dimensional deconstruction, we present 4D models that
fully reproduce the physics of 5D supersymmetric theories compactified on an
S^1/Z_2 orbifold with general Scherk-Schwarz supersymmetry breaking (SSSB)
boundary conditions. In contrast to previous approaches, our deconstruction
involves only soft supersymmetry breaking. Deconstruction preserves many of the
attractive features of SSSB without the cumbersome architecture of a full fifth
dimension, ambiguity of the ultraviolet completion, or challenges associated
with stabilizing a large radius of compactification. We proceed to deconstruct
various five-dimensional models featuring Scherk-Schwarz boundary conditions,
including folded supersymmetry.Comment: 21 pages with appendices, 6 figure
Rescuing Massive Photons from the Swampland
Stringent Swampland conjectures aimed at effective theories containing
massive abelian vectors have recently been proposed (arXiv:1808.09966), with
striking phenomenological implications. In this article, we show how effective
theories that parametrically violate the proposed conjectures can be
UV-completed into theories that satisfy them. The UV-completion is accessible
through both the St\"uckelberg and Higgs mechanisms, with all dimensionless
parameters taking values from the UV perspective. These
constructions feature an IR limit containing a light vector that is
parametrically separated from any other massive states, and from any cut-off
scale mandated by quantum gravity consistency requirements. Moreover, the
cut-off--to--vector--mass ratio remains parametrically large even in the
decoupling limit in which all other massive states (including any scalar
excitations) become arbitrarily heavy. We discuss how apparently strong
constraints imposed by the proposed conjectures on phenomenologically
interesting models, including specific production mechanisms of dark photon
dark matter, are thereby circumvented.Comment: 15 page
Building a Better mSUGRA: WIMP Dark Matter Without Flavor Violation
The appearance of a natural dark matter candidate, the neutralino, is among
the principal successes of minimal supergravity (mSUGRA) and its descendents.
In lieu of a suitable ultraviolet completion, however, theories of
gravity-mediated supersymmetry breaking such as mSUGRA suffer from arbitrary
degrees of flavor violation. Though theories of gauge-mediated supersymmetry
breaking are free from such prohibitive flavor violation, they typically lack
natural neutralino dark matter candidates. Yet this conventional dichotomy
breaks down when the hidden sector is strongly coupled; in models of
gauge-mediated supersymmetry breaking, the neutralino may be the lightest
supersymmetric particle (LSP) if the fields of the hidden sector possess large
anomalous dimensions. In fact, general models of so-called "sequestered" gauge
mediation possess the full richness of neutralino dark matter found in mSUGRA
without corresponding flavor problems. Here we explore generalized models of
sequestered gauge mediation and the rich variety of neutralino dark matter they
exhibit.Comment: 26 pages, 7 figure
Axion-Assisted Electroweak Baryogenesis
We consider a hidden-valley gauge sector, G, with strong coupling scale
Lambda~TeV and CP-violating topological parameter, theta, as well as a new
axion degree of freedom which adjusts theta to near zero in the current
universe. If the G-sector couples to the Standard Model via weak-scale states
charged under both, then in the early universe it is possible for the
CP-violation due to theta (which has not yet been adjusted to zero by the
hidden axion) to feed in to the SM and drive efficient baryogenesis during the
electroweak (EW) phase transition, independent of the effectively small amount
of CP violation present in the SM itself. While current constraints on both the
new axion and charged states are easily satisfied, we argue that the LHC can
investigate the vast majority of parameter space where EW-baryogenesis is
efficiently assisted, while the hidden axion should comprise a significant
fraction of the dark matter density. In the supersymmetric version, the
``messenger'' matter communicating between the SM- and G-sectors naturally
solves the little hierarchy problem of the MSSM. The connection of the hidden
scale and masses of the ``quirk''-like messengers to the EW scale via the
assisted electroweak baryogenesis mechanism provides a reason for such new
hidden valley physics to lie at the weak scale.Comment: 22+1 pages, 3 figure
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