66 research outputs found
Fermion Hierarchy from Sfermion Anarchy
We present a framework to generate the hierarchical flavor structure of
Standard Model quarks and leptons from loops of superpartners. The simplest
model consists of the minimal supersymmetric standard model with tree level
Yukawa couplings for the third generation only and anarchic squark and slepton
mass matrices. Agreement with constraints from low energy flavor observables,
in particular Kaon mixing, is obtained for supersymmetric particles with masses
at the PeV scale or above. In our framework both the second and the first
generation fermion masses are generated at 1-loop. Despite this, a novel
mechanism generates a hierarchy among the first and second generations without
imposing a symmetry or small parameters. A second-to-first generation mass
ratio of order 100 is typical. The minimal supersymmetric standard model thus
includes all the necessary ingredients to realize a fermion spectrum that is
qualitatively similar to observation, with hierarchical masses and mixing. The
minimal framework produces only a few quantitative discrepancies with
observation, most notably the muon mass is too low. We discuss simple
modifications which resolve this and also investigate the compatibility of our
model with gauge and Yukawa coupling Unification.Comment: 42 pages, 11 figure
Large Higgs-electron Yukawa coupling in 2HDM
The present upper bound on , the ratio between the electron Yukawa
coupling and its Standard Model value, is of . We ask what would
be the implications in case that is close to this upper bound. The
simplest extension that allows for such enhancement is that of two Higgs
doublet models (2HDM) without natural flavor conservation. In this framework,
we find the following consequences: (i) Under certain conditions, measuring
and would be enough to predict values of Yukawa couplings
for other fermions and for the and scalars. (ii) In the case that the
scalar potential has a softly broken symmetry, the second Higgs doublet
must be light, but if there is hard breaking of the symmetry, the second Higgs
doublet can be much heavier than the electroweak scale and still allow the
electron Yukawa coupling to be very different from its SM value. (iii) CP must
not be violated at a level higher than in both the
scalar potential and the Yukawa sector. (iv) LHC searches for
resonances constrain this scenario in a significant way. Finally, we study the
implications for models where one of the scalar doublets couples only to the
first generation, or only to the third generation.Comment: 14 pages, 2 figure
GeV-scale dark matter: production at the Main Injector
Assuming that dark matter particles interact with quarks via a GeV-scale
mediator, we study dark matter production in fixed target collisions. The
ensuing signal in a neutrino near detector consists of neutral-current events
with an energy distribution peaked at higher values than the neutrino
background. We find that for a boson of mass around a few GeV that decays
to dark matter particles, the dark matter beam produced by the Main Injector at
Fermilab allows the exploration of a range of values for the gauge coupling
that currently satisfy all experimental constraints. The NOA detector is
well positioned for probing the presence of a dark matter beam, while future
LBNF near-detectors would provide more sensitive probes.Comment: 25 pages, 9 figure
Current and future perspectives of positronium and muonium spectroscopy as dark sectors probe
Positronium and Muonium are purely leptonic atoms and hence free of an
internal sub-structure. This qualifies them as potentially well suited systems
to probe the existence of physics beyond the Standard Model. We hence carry out
a comprehensive study of the sensitivity of current Positronium and Muonium
precision spectroscopy to several new physics scenarios. By taking properly
into account existing experimental and astrophysical probes, we define clear
experimental targets to probe new physics via precise spectroscopy. For
Positronium we find that, in order for the spectroscopy bounds to reach a
sensitivity comparable to the electron gyromagnetic factor, an improvement of
roughly five orders of magnitude from state-of-the-art precision is required,
which would be a challenge based on current technology. More promising is
instead the potential reach of Muonium spectroscopy: in the next few years
experiments like Mu-MASS at PSI will probe new regions of the parameter space
testing the existence of medium/short range (MeV and above) spin-dependent and
spin-independent dark forces between electrons and muons.Comment: 8 pages, 6 figures. Version changed to match journal version. Figures
update
Mixing stops at the LHC
We study the phenomenology of a light stop NLSP in the presence of large
mixing with either the first or the second generation. R-symmetric models
provide a prime setting for this scenario, but our discussion also applies to
the MSSM when a significant amount of mixing can be accommodated. In our
framework the dominant stop decay is through the flavor violating mode into a
light jet and the LSP in an extended region of parameter space. There are
currently no limits from ATLAS and CMS in this region. We emulate shape-based
hadronic SUSY searches for this topology, and find that they have potential
sensitivity. If the extension of these analyses to this region is robust, we
find that these searches can set strong exclusion limits on light stops. If
not, then the flavor violating decay mode is challenging and may represent a
blind spot in stop searches even at 13 TeV. Thus, an experimental investigation
of this scenario is well motivated.Comment: 22 pages, 9 figure
Relaxion and light (pseudo)scalars at the HL-LHC and lepton colliders
We study the potential of future lepton colliders, running at the Z-pole and
above, and the High-Luminosity LHC to search for the relaxion and other light
scalars . We investigate the interplay of direct searches and precision
observables for both CP-even and -odd couplings. In particular, precision
measurements of exotic Z-decays, Higgs couplings, the exotic Higgs decay into a
relaxion pair and associated and production are promising
channels to yield strong bounds.Comment: 27 pages + references, 5 figures, 2 table
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