52 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
Multiverse Dark Matter: SUSY or Axions
The observed values of the cosmological constant {\it and} the abundance of
Dark Matter (DM) can be successfully understood, using certain measures, by
imposing the anthropic requirement that density perturbations go non-linear and
virialize to form halos. This requires a probability distribution favoring low
amounts of DM, i.e. low values of the PQ scale for the QCD axion and low
values of the superpartner mass scale for LSP thermal relics. In
theories with independent scanning of multiple DM components, there is a high
probability for DM to be dominated by a single component. For example, with
independent scanning of and , TeV-scale LSP DM and an axion
solution to the strong CP problem are unlikely to coexist. With thermal LSP DM,
the scheme allows an understanding of a Little SUSY Hierarchy with multi-TeV
superpartners. Alternatively, with axion DM, PQ breaking before (after)
inflation leads to typically below (below) the projected range of the
current ADMX experiment of GeV, providing strong
motivation to develop experimental techniques for probing lower .Comment: 32 pages, 14 figures, version published on JHE
Non-contrastive sentence representations via self-supervision
Sample contrastive methods, typically referred to simply as contrastive are
the foundation of most unsupervised methods to learn text and sentence
embeddings. On the other hand, a different class of self-supervised loss
functions and methods have been considered in the computer vision community and
referred to as dimension contrastive. In this paper, we thoroughly compare this
class of methods with the standard baseline for contrastive sentence
embeddings, SimCSE. We find that self-supervised embeddings trained using
dimension contrastive objectives can outperform SimCSE on downstream tasks
without needing auxiliary loss functions.Comment: Submitted and rejected by EMNLP 2023. Contact the authors for a copy
of the "reviews
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
New Physics from High Energy Tops
Precision measurements of high energy top quarks at the LHC constitute a
powerful probe of new physics. We study the effect of four fermion operators
involving two tops and two light quarks on the high energy tail of the invariant mass distribution. We use existing measurements at a center of
mass energy of 13 TeV, and state of the art calculations of the Standard Model
contribution, to derive bounds on the coefficients of these operators. We
estimate the projected reach of the LHC at higher luminosities and discuss the
validity of these limits within the Effective Field Theory description. We find
that current measurements constrain the mass scale of these operators to be
larger than about 1-2 TeV, while we project that future LHC data will be
sensitive to mass scales of about 3-4 TeV. We apply our bounds to constrain
composite Higgs models with partial compositeness and models with approximate
flavor symmetries. We find our limits to be most relevant to flavor
non-universal models with a moderately large coupling of the heavy new physics
states to third generation quarks.Comment: 13 pages, 2 appendices, 5 figures, references adde
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