245 research outputs found
En-gauging Naturalness
The discovery of a 125.5 GeV Higgs with standard model-like couplings and
naturalness considerations motivate gauge extensions of the MSSM. We analyse
two variants of such an extension and carry out a phenomenological study of
regions of the parameter space satisfying current direct and indirect
constraints, employing state-of-the art two-loop RGE evolution and GMSB
boundary conditions. We find that due to the appearance of non-decoupled
D-terms it is possible to obtain a 125.5 GeV Higgs with stops below 2 TeV,
while the uncolored sparticles could still lie within reach of the LHC. We
compare the contributions of the stop sector and the non-decoupled D-terms to
the Higgs mass, and study their effect on the Higgs couplings. We further
investigate the nature of the next-to lightest supersymmetric particle, in
light of the GMSB motivated searches currently being pursued by ATLAS and CMS.Comment: 45 pages, 17 figures, Supplementary material
SupplementaryQSMxEW-Regime1.pdf attached in source. v2: preprint number added
v3: Appendix A.6, Published in EPJ
Threshold enhancement of diphoton resonances
The data collected by the LHC collaborations at an energy of 13 TeV indicates
the presence of an excess in the diphoton spectrum that would correspond to a
resonance of a 750 GeV mass. The apparently large production cross section is
nevertheless very difficult to explain in minimal models. We consider the
possibility that the resonance is a pseudoscalar boson with a two--photon
decay mediated by a charged and uncolored fermion having a mass at the threshold and a very small decay width, MeV; one can then generate
a large enhancement of the amplitude which explains the excess
without invoking a large multiplicity of particles propagating in the loop,
large electric charges and/or very strong Yukawa couplings. The implications of
such a threshold enhancement are discussed in two explicit scenarios: i) the
Minimal Supersymmetric Standard Model in which the state is produced via
the top quark mediated gluon fusion process and decays into photons
predominantly through loops of charginos with masses close to and
ii) a two Higgs doublet model in which is again produced by gluon fusion
but decays into photons through loops of vector--like charged heavy leptons. We
also comment on a minimal scenario in which the state couples only to
photons through a heavy lepton loop and is both produced and decays through
this coupling. In all these scenarios, while the mass of the charged fermion
has to be adjusted to be extremely close to half of the resonance mass, the
small total widths are naturally obtained if only suppressed three-body decay
channels occur. Finally, the implications of some of these scenarios for dark
matter are discussed.Comment: 15 pages, 4 figures, version submitted to journal with typos
correcte
The Dark Side of Electroweak Naturalness Beyond the MSSM
Weak scale supersymmetry (SUSY) remains a prime explanation for the radiative
stability of the Higgs field. A natural account of the Higgs boson mass,
however, strongly favors extensions of the Minimal Supersymmetric Standard
Model (MSSM). A plausible option is to introduce a new supersymmetric sector
coupled to the MSSM Higgs fields, whose associated states resolve the little
hierarchy problem between the third generation squark masses and the weak
scale. SUSY also accomodates a weakly interacting cold dark matter (DM)
candidate in the form of a stable neutralino. In minimal realizations, the
thus-far null results of direct DM searches, along with the DM relic abundance
constraint, introduce a level of fine-tuning as severe as the one due to the
SUSY little hierarchy problem. We analyse the generic implications of new SUSY
sectors parametrically heavier than the minimal SUSY spectrum, devised to
increase the Higgs boson mass, on this little neutralino DM problem. We focus
on the SUSY operator of smallest scaling dimension in an effective field theory
description, which modifies the Higgs and DM sectors in a correlated manner.
Within this framework, we show that recent null results from the LUX experiment
imply a tree-level fine-tuning for gaugino DM which is parametrically at least
a few times larger than that of the MSSM. Higgsino DM whose relic abundance is
generated through a thermal freeze-out mechanism remains also severely
fine-tuned, unless the DM lies below the weak boson pair-production threshold.
As in the MSSM, well-tempered gaugino-Higgsino DM is strongly disfavored by
present direct detection results.Comment: 41 pages, 8 figures, references adde
Clockworking FIMPs
We study freeze-in dark matter production in models that rely on the
Clockwork mechanism to suppress the dark matter couplings to the visible
sector. We construct viable scalar and fermionic dark matter models within this
Clockwork FIMP scenario, with several subtleties that need to be taken into
account revealed in the model-building process. We also provide analytic,
semi-analytic and numerical results for the diagonalization of Clockwork-type
mass matrices and briefly discuss the LHC phenomenology of the corresponding
scenarios.Comment: 27 pages, 3 figures. Some typos in the appendices corrected. Accepted
for JHE
One jet to rule them all: monojet constraints and invisible decays of a 750 GeV diphoton resonance
The ATLAS and CMS collaborations recently reported a mild excess in the
diphoton final state pointing to a resonance with a mass of around 750 GeV and
a potentially large width. We consider the possibility of a scalar resonance
being produced via gluon fusion and decaying to electroweak gauge bosons, jets
and pairs of invisible particles, stable at collider scales. We compute limits
from monojet searches on such a resonance and test their compatibility with the
requirement for a large width. We also study whether the stable particle can be
a a dark matter candidate and investigate the corresponding relic density
constraints along with the collider limits. We show that monojet searches rule
out a large part of the available parameter space and point out scenarios where
a broad diphoton resonance can be reconciled with monojet constraints.Comment: Matches published versio
Isospin-violating dark matter from a double portal
We study a simple model that can give rise to isospin-violating interactions
of Dirac fermion asymmetric dark matter to protons and neutrons through the
interference of a scalar and U(1) gauge boson contribution. The model can
yield a large suppression of the elastic scattering cross section off Xenon
relative to Silicon thus reconciling CDMS-Si and LUX results while being
compatible with LHC findings on the 126 GeV Higgs, electroweak precision tests
and flavour constraints.Comment: 25 pages, 7 figure
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