578 research outputs found
A New Look at Higgs Constraints on Stops
We present a simple new way to visualize the constraints of Higgs coupling
measurements on light stops in natural SUSY scenarios beyond the MSSM, which
works directly in the plane of stop mass eigenvalues (with no need to make
assumptions about mixing angles). For given stop mass eigenvalues, the smallest
value of that can bring the correction to the and couplings into agreement with data is computed. Requiring that
this is consistent--i.e. that the chosen mass eigenvalues can be the
outcome of diagonalizing a matrix with a given off-diagonal term--rules out the
possibility that both stops have a mass below 400 GeV. Requiring that
is not fine-tuned for agreement with the data shows that neither stop can
be lighter than 100 GeV. These constraints are interesting because,
unlike direct searches, they apply no matter how stops decay, and suggest a
minimum electroweak fine-tuning of between a factor of 5 and 10. We show that a
multi-parameter fit can slightly weaken this conclusion by allowing a large
Higgs coupling to -quarks, but only if a second Higgs boson is within reach
of experiment. Certain models, like -symmetric models with Dirac gauginos,
are much more strongly constrained because they predict negligible . We
illustrate how the constraints will evolve given precise measurements at future
colliders (HL-LHC, ILC, and TLEP), and comment on the more difficult case of
Folded Supersymmetry.Comment: v2: references added, accepted by JHE
Electric Dipole Moments in Natural Supersymmetry
We discuss electric dipole moments (EDMs) in the framework of CP-violating
natural supersymmetry (SUSY). Recent experimental results have significantly
tightened constraints on the EDMs of electrons and of mercury, and substantial
further progress is expected in the near future. We assess how these results
constrain the parameter space of natural SUSY. In addition to our discussion of
SUSY, we provide a set of general formulas for two-loop fermion EDMs, which can
be applied to a wide range of models of new physics. In the SUSY context, the
two-loop effects of stops and charginos respectively constrain the phases of
and to be small in the natural part of parameter space. If
the Higgs mass is lifted to 125 GeV by a new tree-level superpotential
interaction and soft term with CP-violating phases, significant EDMs can arise
from the two-loop effects of bosons and tops. We compare the bounds arising
from EDMs to those from other probes of new physics including colliders, , and dark matter searches. Importantly, improvements in reach not
only constrain higher masses, but require the phases to be significantly
smaller in the natural parameter space at low mass. The required smallness of
phases sharpens the CP problem of natural SUSY model building.Comment: 37 pages plus appendices, 16 figures; v2: journal versio
Top Partners at the LHC: Spin and Mass Measurement
If one takes naturalness seriously and also assumes a weakly coupled
extension of the Standard Model (SM) then there are predictions for
phenomenology that can be inferred in a model independent framework. The first
such prediction is that there must be some colored particle with mass O(TeV)
that cancels the top loop contribution to the quadratic divergence of the Higgs
mass. In this paper we begin a model independent analysis of the phenomenology
of this "top partner," t'. We make one additional assumption that it is odd
under a parity which is responsible for the stability of a WIMP dark matter
candidate, N. We focus on three questions to be explored at the LHC: discovery
opportunities, mass determination, and spin determination of this top partner.
We find that within a certain region of masses for the t' and N, t'\bar{t'} is
easily discovered in the t\bar{t}+2N decay with the tops decaying fully
hadronically. We show that without having to rely on other channels for new
physics that for a a given t' spin the masses of t' and N can be measured using
kinematic information (e.g. average MET or H_T) and total cross section. A
degeneracy due to the spin remains, but with several hundred inverse fb of
luminosity we demonstrate potentially useful new methods for determining the t'
spin over a wide range of masses. Our methods could be useful for
distinguishing supersymmetric and non-supersymmetric models.Comment: 28 pages, 5 figure
Continuum-Mediated Dark Matter-Baryon Scattering
Many models of dark matter scattering with baryons may be treated either as a
simple contact interaction or as the exchange of a light mediator particle. We
study an alternative, in which a continuum of light mediator states may be
exchanged. This could arise, for instance, from coupling to a sector which is
approximately conformal at the relevant momentum transfer scale. In the
non-relativistic effective theory of dark matter-baryon scattering, which is
useful for parametrizing direct detection signals, the effect of such continuum
mediators is to multiply the amplitude by a function of the momentum transfer
q, which in the simplest case is just a power law. We develop the basic
framework and study two examples: the case where the mediator is a scalar
operator coupling to the Higgs portal (which turns out to be highly
constrained) and the case of an antisymmetric tensor operator that mixes with the hypercharge field strength and couples to dark matter
tensor currents, which has an interesting viable parameter space. We describe
the effect of such mediators on the cross sections and recoil energy spectra
that could be observed in direct detection.Comment: 30 pages, 6 figures. v2: minor changes, references adde
The Weak Gravity Conjecture and Emergence from an Ultraviolet Cutoff
We study ultraviolet cutoffs associated with the Weak Gravity Conjecture
(WGC) and Sublattice Weak Gravity Conjecture (sLWGC). There is a magnetic WGC
cutoff at the energy scale with an associated sLWGC tower of
charged particles. A more fundamental cutoff is the scale at which gravity
becomes strong and field theory breaks down entirely. By clarifying the nature
of the sLWGC for nonabelian gauge groups we derive a parametric upper bound on
this strong gravity scale for arbitrary gauge theories. Intriguingly, we show
that in theories approximately saturating the sLWGC, the scales at which loop
corrections from the tower of charged particles to the gauge boson and graviton
propagators become important are parametrically identical. This suggests a
picture in which gauge fields emerge from the quantum gravity scale by
integrating out a tower of charged matter fields. We derive a converse
statement: if a gauge theory becomes strongly coupled at or below the quantum
gravity scale, the WGC follows. We sketch some phenomenological consequences of
the UV cutoffs we derive.Comment: 50 pages, 5 figures. v2: references added, clarified remarks about
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