5,024 research outputs found
Naturalness after LHC8
I review the status of naturalness of the weak scale after the results from
the LHC operating at an energy of 8 TeV. Talk delivered at the 2013 Europhysics
Conference on High Energy Physics (EPS), Stockholm, Sweden, 18-24 July 2013.Comment: 13 pages, 1 figure; 2013 EPS Conference Proceeding
A new ansatz for quark and lepton mass matrices
A new ansatz for quark and lepton mass matrices is proposed in the context of
supersymmetric grand unified theories. The 13 parameters describing fermion
masses and mixings are determined in terms of only 6 free parameters, allowing
7 testable predictions. The values of , , , ,
, , and are then predicted as a function of the 3 charged
lepton masses, , , and , the ratio of Higgs vacuum
expectation values. In particular the Cabibbo angle and are
determined in terms of only lepton masses. All predictions are in very good
agreement with experiments.Comment: 10 page
Beyond the Standard Model
Elementary introduction to physics beyond the Standard Model. Lectures
delivered at the 1995 European School of High-Energy Physics in Dubna, Russia.Comment: 19 page
Recent Developments in Physics Beyond the Standard Model
In this talk I discuss some recent developments in physics beyond the
Standard Model. After some initial comments on neutrino masses, I discuss the
status of low-energy supersymmetry and finally turn to describing some recent
work in theories with extra spatial dimensions. Plenary talk at the XIX
International Symposium on Lepton and Photon Interactions at High Energies,
Stanford University, 9-14 August 1999.Comment: 25 pages, 2 eps figure
Nearly Degenerate Gauginos and Dark Matter at the LHC
Motivated by dark-matter considerations in supersymmetric theories, we
investigate in a fairly model-independent way the detection at the LHC of
nearly degenerate gauginos with mass differences between a few GeV and about 30
GeV. Due to the degeneracy of gaugino states, the conventional leptonic signals
are likely lost. We first consider the leading signal from gluino production
and decay. We find that it is quite conceivable to reach a large statistical
significance for the multi-jet plus missing energy signal with an integrated
luminosity about 50 pb^-1 (50 fb^-1) for a gluino mass of 500 GeV (1 TeV). If
gluinos are not too heavy, less than about 1.5 TeV, this channel can typically
probe gaugino masses up to about 100 GeV below the gluino mass. We then study
the Drell-Yan type of gaugino pair production in association with a hard QCD
jet, for gaugino masses in the range of 100-150 GeV. The signal observation may
be statistically feasible with about 10 fb^-1, but systematically challenging
due to the lack of distinctive features for the signal distributions. By
exploiting gaugino pair production through weak boson fusion, signals of large
missing energy plus two forward-backward jets may be observable at a 4-6\sigma
level above the large SM backgrounds with an integrated luminosity of 100-300
fb^-1. Finally, we point out that searching for additional isolated soft muons
in the range p_T ~3-10 GeV in the data samples discussed above may help to
enrich the signal and to control the systematics. Significant efforts are made
to explore the connection between the signal kinematics and the relevant masses
for the gluino and gauginos, to probe the mass scales of the superpartners, in
particular the LSP dark matter.Comment: 35 pages, 32 figure
Split Supersymmetry
The naturalness criterion applied to the cosmological constant implies a
new-physics threshold at 10^-3 eV. Either the naturalness criterion fails, or
this threshold does not influence particle dynamics at higher energies. It has
been suggested that the Higgs naturalness problem may follow the same fate. We
investigate this possibility and, abandoning the hierarchy problem, we use
unification and dark matter as the only guiding principles. The model recently
proposed by Arkani-Hamed and Dimopoulos emerges as a very interesting option.
We study it in detail, analysing its structure, and the conditions for
obtaining unification and dark matter.Comment: 29 pages, comments, corrections and references adde
A Clockwork Theory
The clockwork is a mechanism for generating light particles with
exponentially suppressed interactions in theories which contain no small
parameters at the fundamental level. We develop a general description of the
clockwork mechanism valid for scalars, fermions, gauge bosons, and gravitons.
This mechanism can be implemented with a discrete set of new fields or, in its
continuum version, through an extra spatial dimension. In both cases the
clockwork emerges as a useful tool for model-building applications. Notably,
the continuum clockwork offers a solution to the Higgs naturalness problem,
which turns out to be the same as in linear dilaton duals of Little String
Theory. We also elucidate the similarities and differences of the continuum
clockwork with large extra dimensions and warped spaces. All clockwork models,
in the discrete and continuum, exhibit novel phenomenology with a distinctive
spectrum of closely spaced resonances.Comment: Body of text 26 page
R-Parity Violation and Unification
The reported anomaly in deep-inelastic scattering at HERA has revived
interest in the phenomenology of R-parity violation. From the theoretical point
of view, the existence of R-violating interactions poses two considerable
problems. The first one concerns the flavour structure of the interactions and
the origin of an appropriate suppression of flavour-changing neutral-current
processes and lepton-family transitions. The second one concerns the way of
embedding R-violating interactions in a grand unified theory (GUT) without
introducing unacceptable nucleon decay rates. We show that the second problem
can be solved by a mechanism which is purely group theoretical and does not
rely on details of the flavour theory. We construct explicit GUT models in
which our mechanism can be realized.Comment: Flipped SU(5) example modified. Conclusions unchange
Gauge Coupling Unification in MSSM + 5 Flavors
We investigate gauge coupling unification at 2-loops for theories with 5
extra vectorlike SU(5) fundamentals added to the MSSM. This is a borderline
case where unification is only predicted in certain regions of parameter space.
We establish a lower bound on the scale for the masses of the extra flavors, as
a function of the sparticle masses. Models far outside of the bound do not
predict unification at all (but may be compatible with unification), and models
outside but near the boundary cannot reliably claim to predict it with an
accuracy comparable to the MSSM prediction. Models inside the boundary can work
just as well as the MSSM.Comment: 28 pages, 13 figures. Added references, fixed minor typos. No changes
to content. Page count was incorrect in v1 Comment
Starobinsky-like inflation from induced gravity
We derive a general criterion that defines all single-field models leading to
Starobinsky-like inflation and to universal predictions for the spectral index
and tensor-to-scalar ratio, which are in agreement with Planck data. Out of all
the theories that satisfy this criterion, we single out a special class of
models with the interesting property of retaining perturbative unitarity up to
the Planck scale. These models are based on induced gravity, with the Planck
mass determined by the vacuum expectation value of the inflaton.Comment: 13 pages; some references added; version published in PL
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