46 research outputs found
A modified naturalness principle and its experimental tests
Motivated by LHC results, we modify the usual criterion for naturalness by
ignoring the uncomputable power divergences. The Standard Model satisfies the
modified criterion ('finite naturalness') for the measured values of its
parameters. Extensions of the SM motivated by observations (Dark Matter,
neutrino masses, the strong CP problem, vacuum instability, inflation) satisfy
finite naturalness in special ranges of their parameter spaces which often
imply new particles below a few TeV. Finite naturalness bounds are weaker than
usual naturalness bounds because any new particle with SM gauge interactions
gives a finite contribution to the Higgs mass at two loop order.Comment: 17 pages, 3 figures. v3: final version uploaded, references added,
numerical error in the last column of table 1 fixe
THE NEXT TO MINIMAL SUPERSYMMETRIC STANDARD MODEL WITH A MODERATE STOP MASS
In this thesis we analize the Next to Minimal Supersymmetric Standard Model (NMSSM), looking for a natural electroweak symmetry breaking. Focusing on a moderate stop mass and requiring perturbative unification of the gauge couplings (which after all is a very good prediction of the MSSM), we put quite severe restrictions on the parameter space. In particular if we do not modify the theory any further we find that we must live with a small and . Even in this limit a SM like Higgs boson, which is present in the spectrum, barely touches the LEP2 mass bound.
We show that we can improve on this situation if we allow vectorlike multiplets of extra symmetric matter to be present at intermediate energies. This matter, while not disturbing unification, allows for a higher value of at the Fermi scale, in such a way that we are able to obtain a Higgs boson mass as big as .
At this point we analyze a particular realization of this picture in the corner of the NMSSM parameter space where , thus saturating the upper limit on at the weak scale. Setting to zero the triliner self interaction of the singlet superfield in the superpotential, restores a Peccei-Quinn symmetry in the action which is welcome to solve the problem. A small explicit breaking of such a symmetry is required to give mass to a (pseudo-)Goldstone boson which would be otherwise experimentally excluded
Radiative PQ Breaking and the Higgs Boson Mass
The small and negative value of the Standard Model Higgs quartic coupling at
high scales can be understood in terms of anthropic selection on a landscape
where large and negative values are favored: most universes have a very
short-lived electroweak vacuum and typical observers are in universes close to
the corresponding metastability boundary. We provide a simple example of such a
landscape with a Peccei-Quinn symmetry breaking scale generated through
dimensional transmutation and supersymmetry softly broken at an intermediate
scale. Large and negative contributions to the Higgs quartic are typically
generated on integrating out the saxion field. Cancellations among these
contributions are forced by the anthropic requirement of a sufficiently
long-lived electroweak vacuum, determining the multiverse distribution for the
Higgs quartic in a similar way to that of the cosmological constant. This leads
to a statistical prediction of the Higgs boson mass that, for a wide range of
parameters, yields the observed value within the 1 statistical
uncertainty of 5 GeV originating from the multiverse distribution. The
strong CP problem is solved and single-component axion dark matter is
predicted, with an abundance that can be understood from environmental
selection. A more general setting for the Higgs mass prediction is discussed.Comment: 30 pages, 10 figures; v2, JHEP versio
A Fourth Exception in the Calculation of Relic Abundances
We propose that the dark matter abundance is set by the decoupling of
inelastic scattering instead of annihilations. This coscattering mechanism is
generically realized if dark matter scatters against states of comparable mass
from the thermal bath. Coscattering points to dark matter that is exponentially
lighter than the weak scale and has a suppressed annihilation rate, avoiding
stringent constraints from indirect detection. Dark matter upscatters into
states whose late decays can lead to observable distortions to the blackbody
spectrum of the cosmic microwave background.Comment: 8 pages, 6 figures. V3: figure adde
Heavy Vector Triplets: Bridging Theory and Data
We introduce a model-independent strategy to study narrow resonances which we
apply to a heavy vector triplet of the Standard Model (SM) group for
illustration. The method is based on a simplified phenomenological Lagrangian
which reproduces a large class of explicit models. Firstly, this allows us to
derive robust model-independent phenomenological features and, conversely, to
identify the peculiarities of different explicit realizations. Secondly, limits
on cross-section times BR can be converted into bounds on a few relevant
parameters in a fully analytic way, allowing for an interpretation in any given
explicit model. Based on the available 8 TeV LHC analyses, we derive current
limits and interpret them for vector triplets arising in weakly coupled (gauge)
and strongly coupled (composite) extensions of the SM. We point out that a
model-independent limit setting procedure must be based on purely on-shell
quantities, like a cross-section times BR. Finite width effects altering the
limits can be considerably reduced by focusing on the on-shell signal region.
We illustrate this aspect with a study of the invariant mass distribution in
di-lepton searches and the transverse mass distribution in lepton-neutrino
final states. In addition to this paper we provide a set of online tools
available at a dedicated webpage.Comment: 53 pages, 10 figures; references added, typos corrected; published
versio
Precision Probes of QCD at High Energies
New physics, that is too heavy to be produced directly, can leave measurable
imprints on the tails of kinematic distributions at the LHC. We use energetic
QCD processes to perform novel measurements of the Standard Model (SM)
Effective Field Theory. We show that the dijet invariant mass spectrum, and the
inclusive jet transverse momentum spectrum, are sensitive to a dimension 6
operator that modifies the gluon propagator at high energies. The dominant
effect is constructive or destructive interference with SM jet production. We
compare differential next-to-leading order predictions from POWHEG to public 7
TeV jet data, including scale, PDF, and experimental uncertainties and their
respective correlations. We constrain a New Physics (NP) scale of 3.5 TeV with
current data. We project the reach of future 13 and 100 TeV measurements, which
we estimate to be sensitive to NP scales of 8 and 60 TeV, respectively. As an
application, we apply our bounds to constrain heavy vector octet colorons that
couple to the QCD current. We project that effective operators will surpass
bump hunts, in terms of coloron mass reach, even for sequential couplings.Comment: 40 pages, 13 figures, 8 tables. Minor changes. Accepted on JHE
Minimal Matter at the Large Hadron Collider
We classify all possible new U(1) x SU(2) x SU(3) multiplets that can couple
to pairs of SM particles. Assuming that production of such new particles is
dominated by their gauge interactions we study their signals at LHC, finding
the following five main classes: i) lepto-quark 2l 2q signals; ii) di-lepton 4l
signals; iii) di-quarks 4j signals, iv) heavy-lepton 2l 2V signals and v) heavy
quarks 2j 2V signals, where V denotes heavy SM vectors (with W being associated
to exotic fermions). In each case we outilne the most promising final states,
the SM backgrounds and propose the needed searches.Comment: 24 pages, 10 figures. Typos fixed; Addendum about the capabilities of
the on-going LHC run at 7 Te