50 research outputs found
The New Flavor of Higgsed Gauge Mediation
Recent LHC bounds on squark masses combined with naturalness and flavor
considerations motivate non-trivial sfermion mass spectra in the supersymmetric
Standard Model. These can arise if supersymmetry breaking is communicated to
the visible sector via new extended gauge symmetries. Such extended symmetries
must be spontaneously broken, or confined, complicating the calculation of soft
masses. We develop a new formalism for calculating perturbative gauge-mediated
two-loop soft masses for gauge groups with arbitrary patterns of spontaneous
symmetry breaking, simplifying the framework of "Higgsed gauge mediation." The
resulting expressions can be applied to Abelian and non-Abelian gauge groups,
opening new avenues for supersymmetric model building. We present a number of
examples using our method, ranging from grand unified threshold corrections in
standard gauge mediation to soft masses in gauge extensions of the Higgs sector
that can raise the Higgs mass through non-decoupling D-terms. We also outline a
new mediation mechanism called "flavor mediation", where supersymmetry breaking
is communicated via a gauged subgroup of Standard Model flavor symmetries.
Flavor mediation can automatically generate suppressed masses for
third-generation squarks and implies a nearly exact U(2) symmetry in the first
two generations, yielding a "natural SUSY" spectrum without imposing ad hoc
global symmetries or giving preferential treatment to particular generations.Comment: 13 pages, 3 figures; v2: typos corrected, references adde
Multiple Gamma Lines from Semi-Annihilation
Hints in the Fermi data for a 130 GeV gamma line from the galactic center
have ignited interest in potential gamma line signatures of dark matter.
Explanations of this line based on dark matter annihilation face a parametric
tension since they often rely on large enhancements of loop-suppressed cross
sections. In this paper, we pursue an alternative possibility that dark matter
gamma lines could arise from "semi-annihilation" among multiple dark sector
states. The semi-annihilation reaction with a single final state photon is
typically enhanced relative to ordinary annihilation into photon pairs.
Semi-annihilation allows for a wide range of dark matter masses compared to the
fixed mass value required by annihilation, opening the possibility to explain
potential dark matter signatures at higher energies. The most striking
prediction of semi-annihilation is the presence of multiple gamma lines, with
as many as order N^3 lines possible for N dark sector states, allowing for dark
sector spectroscopy. A smoking gun signature arises in the simplest case of
degenerate dark matter, where a strong semi-annihilation line at 130 GeV would
be accompanied by a weaker annihilation line at 173 GeV. As a proof of
principle, we construct two explicit models of dark matter semi-annihilation,
one based on non-Abelian vector dark matter and the other based on retrofitting
Rayleigh dark matter.Comment: 15 pages of text, 8 figures. v2: refs adde
Colorful Twisted Top Partners and Partnerium at the LHC
In scenarios that stabilize the electroweak scale, the top quark is typically
accompanied by partner particles. In this work, we demonstrate how extended
stabilizing symmetries can yield scalar or fermionic top partners that
transform as ordinary color triplets but carry exotic electric charges. We
refer to these scenarios as "hypertwisted" since they involve modifications to
hypercharge in the top sector. As proofs of principle, we construct two
hypertwisted scenarios: a supersymmetric construction with spin-0 top partners,
and a composite Higgs construction with spin-1/2 top partners. In both cases,
the top partners are still phenomenologically compatible with the mass range
motivated by weak-scale naturalness. The phenomenology of hypertwisted
scenarios is diverse, since the lifetimes and decay modes of the top partners
are model dependent. The novel coupling structure opens up search channels that
do not typically arise in top-partner scenarios, such as pair production of
top-plus-jet resonances. Furthermore, hypertwisted top partners are typically
sufficiently long lived to form "top-partnerium" bound states that decay
predominantly via annihilation, motivating searches for rare narrow resonances
with diboson decay modes.Comment: 39 pages, 6 figures; v2: added minor clarifications and references;
published versio
Ideals with Larger Projective Dimension and Regularity
We define a family of homogeneous ideals with large projective dimension and
regularity relative to the number of generators and their common degree. This
family subsumes and improves upon constructions given in [Cav04] and [McC]. In
particular, we describe a family of three-generated homogeneous ideals in
arbitrary characteristic whose projective dimension grows asymptotically as
sqrt{d}^(sqrt(d) - 1).Comment: 10 pages. This work was completed at the MRC for Commutative Algebra
in Snowbird, UT, which was generously supported by the AM
1001-25 Primary results of the rapid emergency department heart failure outpatient trial (REDHOT): A multicenter trial examining B-type natriuretic peptide levels, emergency physician decision making and outcomes in patients presenting with shortness of breath
The Spectrum of Goldstini and Modulini
When supersymmetry is broken in multiple sectors via independent dynamics,
the theory furnishes a corresponding multiplicity of "goldstini" degrees of
freedom which may play a substantial role in collider phenomenology and
cosmology. In this paper, we explore the tree-level mass spectrum of goldstini
arising from a general admixture of F-term, D-term, and almost no-scale
supersymmetry breaking, employing non-linear superfields and a novel gauge
fixing for supergravity discussed in a companion paper. In theories of F-term
and D-term breaking, goldstini acquire a mass which is precisely twice the
gravitino mass, while the inclusion of no-scale breaking renders one of these
modes, the modulino, massless. We argue that the vanishing modulino mass can be
explained in terms of an accidental and spontaneously broken "global"
supersymmetry.Comment: 10 pages, 2 figures; v2: typo corrected, references updated; v3:
version to appear in JHE
Flavor Mediation Delivers Natural SUSY
If supersymmetry (SUSY) solves the hierarchy problem, then naturalness
considerations coupled with recent LHC bounds require non-trivial superpartner
flavor structures. Such "Natural SUSY" models exhibit a large mass hierarchy
between scalars of the third and first two generations as well as degeneracy
(or alignment) among the first two generations. In this work, we show how this
specific beyond the standard model (SM) flavor structure can be tied directly
to SM flavor via "Flavor Mediation". The SM contains an anomaly-free SU(3)
flavor symmetry, broken only by Yukawa couplings. By gauging this flavor
symmetry in addition to SM gauge symmetries, we can mediate SUSY breaking via
(Higgsed) gauge mediation. This automatically delivers a natural SUSY spectrum.
Third-generation scalar masses are suppressed due to the dominant breaking of
the flavor gauge symmetry in the top direction. More subtly, the
first-two-generation scalars remain highly degenerate due to a custodial U(2)
symmetry, where the SU(2) factor arises because SU(3) is rank two. This
custodial symmetry is broken only at order (m_c/m_t)^2. SUSY gauge coupling
unification predictions are preserved, since no new charged matter is
introduced, the SM gauge structure is unaltered, and the flavor symmetry treats
all matter multiplets equally. Moreover, the uniqueness of the anomaly-free
SU(3) flavor group makes possible a number of concrete predictions for the
superpartner spectrum.Comment: 17 pages, 7 figures, 2 tables. v2 references added, minor changes to
flavor constraints and a little discussion adde
Pathways to ischemic neuronal cell death: are sex differences relevant?
We have known for some time that the epidemiology of human stroke is sexually dimorphic until late in life, well beyond the years of reproductive senescence and menopause. Now, a new concept is emerging: the mechanisms and outcome of cerebral ischemic injury are influenced strongly by biological sex as well as the availability of sex steroids to the brain. The principal mammalian estrogen (17 β estradiol or E2) is neuroprotective in many types of brain injury and has been the major focus of investigation over the past several decades. However, it is becoming increasingly clear that although hormones are a major contributor to sex-specific outcomes, they do not fully account for sex-specific responses to cerebral ischemia. The purpose of this review is to highlight recent studies in cell culture and animal models that suggest that genetic sex determines experimental stroke outcome and that divergent cell death pathways are activated after an ischemic insult. These sex differences need to be identified if we are to develop efficacious neuroprotective agents for use in stroke patients
Visible Supersymmetry Breaking and an Invisible Higgs
If there are multiple hidden sectors which independently break supersymmetry,
then the spectrum will contain multiple goldstini. In this paper, we explore
the possibility that the visible sector might also break supersymmetry, giving
rise to an additional pseudo-goldstino. By the standard lore, visible sector
supersymmetry breaking is phenomenologically excluded by the supertrace sum
rule, but this sum rule is relaxed with multiple supersymmetry breaking.
However, we find that visible sector supersymmetry breaking is still
phenomenologically disfavored, not because of a sum rule, but because the
visible sector pseudo-goldstino is generically overproduced in the early
universe. A way to avoid this cosmological bound is to ensure that an R
symmetry is preserved in the visible sector up to supergravity effects. A key
expectation of this R-symmetric case is that the Higgs boson will dominantly
decay invisibly at the LHC.Comment: v1 - 27 pages, 13 figures, 1 table; v2 - references added; v3 -
expanded discussion of higgs sector, JHEP versio