47 research outputs found
Little hierarchy in the minimally specified MSSM
We study constrained versions of the minimal supersymmetric model and
investigate the hierarchy between the electroweak scale and the scale of
superpartners that can be achieved without relying on specifying model
parameters by more than one digit. This approach automatically avoids scenarios
in which a large hierarchy is obtained by special choices of parameters and yet
keeps scenarios that would be otherwise disfavored by various sensitivity
measures. We consider models with universal gaugino and scalar masses, models
with non-universal Higgs masses or non-universal gaugino masses and focus on
scenarios in which all the model parameters are either of the same order or
zero at the grand unification scale. We find that the maximal hierarchy between
the electroweak scale and stop masses, requiring that model parameters are not
specified beyond one digit, ranges from a factor of for the CMSSM
up to for models with non-universal Higgs or gaugino masses.Comment: 17 pages, 4 figures, discussion expanded, matches published versio
Mass scale of vectorlike matter and superpartners from IR fixed point predictions of gauge and top Yukawa couplings
We use the IR fixed point predictions for gauge couplings and the top Yukawa
coupling in the MSSM extended with vectorlike families to infer the scale of
vectorlike matter and superpartners. We quote results for several extensions of
the MSSM and present results in detail for the MSSM extended with one complete
vectorlike family. We find that for a unified gauge coupling
vectorlike matter or superpartners are expected within 1.7 TeV (2.5 TeV) based
on all three gauge couplings being simultaneously within 1.5\% (5\%) from
observed values. This range extends to about 4 TeV for . We
also find that in the scenario with two additional large Yukawa couplings of
vectorlike quarks the IR fixed point value of the top Yukawa coupling
independently points to a multi-TeV range for vectorlike matter and
superpartners. Assuming a universal value for all large Yukawa couplings at the
GUT scale, the measured top quark mass can be obtained from the IR fixed point
for . The range expands to any for
significant departures from the universality assumption. Considering that the
Higgs boson mass also points to a multi-TeV range for superpartners in the
MSSM, adding a complete vectorlike family at the same scale provides a
compelling scenario where the values of gauge couplings and the top quark mass
are understood as a consequence of the particle content of the model.Comment: 31 pages, 9 figures, typos corrected, matches the published version.
v4: Appendix correcte
Top-bottom-tau Yukawa coupling unification in the MSSM+1VF and fermion masses as IR fixed points
In the MSSM extended by a complete vectorlike family, precise top, bottom and
tau Yukawa coupling unification can be achieved assuming SUSY threshold
corrections which are typical for comparable superpartner masses. Furthermore,
the unification is possible with a large unified coupling, implying that all
three fermion masses can be simultaneously close to their IR fixed points.
Assuming unified Yukawa couplings of order one or larger, the preferred common
scale of new physics (superpartners and vectorlike matter) is in the 3 TeV to
30 TeV range, with larger couplings favoring smaller scales. Splitting
superpartner masses from masses of vectorlike fields, the preferred scales
extend in both directions. The multi-TeV scale for superpartners is compatible
with and independently suggested by the Higgs boson mass.Comment: v2: matches published versio
Seven largest couplings of the standard model as IR fixed points
We report on an intriguing observation that the values of all the couplings
in the standard model except those related to first two generations can be
understood from the IR fixed point structure of renormalization group equations
in the minimal supersymmetric model extended by one complete vectorlike family
with the scale of new physics in a multi-TeV range.Comment: 5 pages, 3 figures, discussion added, matches published versio
Relic Challenges for Vector-Like Fermions as Connectors to a Dark Sector
New dark sectors consisting of exotic fields that couple only very feebly to
the Standard Model (SM) have strong theoretical motivation and may be relevant
to explaining the abundance of dark matter (DM). An important question for such
sectors is how they connect to the SM. For a dark sector with a new gauge
interaction, a natural connection arises from heavy vector-like fermions
charged under both the visible and dark gauge groups. The gauge charges of such
fermions imply that one or more of them is stable in the absence of additional
sources of dark symmetry breaking. A generic challenge for such connectors is
that they can produce too much dark matter or interact too strongly with nuclei
if they were ever thermalized in the early universe. In this paper we study
this challenge in a simple connector theory consisting of new vector-like
electroweak doublet and singlet fermions that also transform under the
fundamental representation of a new (Abelian) gauge force, and we show that
these connectors in their minimal form are almost always ruled out by existing
direct DM searches. To address this challenge, we investigate two solutions.
First, we study mitigating scattering on nuclei by introducing a Majorana mass
term for the singlet. And second, we investigate a mixing with SM leptons that
allows the connectors to decay while remaining consistent with cosmological
tests and searches for charged lepton flavor violation. Both solutions rely on
the presence of a dark Higgs field with a specific charge.Comment: 32 pages, 5 figures, added references, corrected plotting error,
conclusions unchange
Predictions for Muon Electric and Magnetic Dipole Moments from in Two-Higgs-Doublet Models with New Leptons
We calculate chirally-enhanced corrections to the muon's electric and
magnetic dipole moments in two-Higgs-doublet models extended by vectorlike
leptons, and we explore a sharp correlation between
and the muon's dipole moments in these models. Among many detailed predictions,
for a model with new leptons with the same quantum numbers as standard model
leptons, we find that necessarily
requires a muon electric dipole moment to be observed at near-future
experiments, assuming is measured within of
the standard model prediction for the current central value of the measured
muon magnetic moment. In all studied models, the predicted values of the
electric dipole moment can reach up to current experimental limits. Moreover,
we show that in some models there can be two sources of chiral enhancement,
parameterizing the correlation between and the
dipole moments by a complex number. This leads to sign-preferred predictions
for the electric dipole moment.Comment: 26 pages + 25 pages of appendices, 9 figure