16,548 research outputs found
Finding the Standard Model of Particle Physics, A Combinatorial Problem
We present a combinatorial problem which consists in finding irreducible
Krajewski diagrams from finite geometries. This problem boils down to placing
arrows into a quadratic array with some additional constrains. The Krajewski
diagrams play a central role in the description of finite noncommutative
geometries. They allow to localise the standard model of particle physics
within the set of all Yang-Mills-Higgs models
Measuring Invisible Particle Masses Using a Single Short Decay Chain
We consider the mass measurement at hadron colliders for a decay chain of two
steps, which ends with a missing particle. Such a topology appears as a
subprocess of signal events of many new physics models which contain a dark
matter candidate. From the two visible particles coming from the decay chain,
only one invariant mass combination can be formed and hence it is na\"ively
expected that the masses of the three invisible particles in the decay chain
cannot be determined from a single end point of the invariant mass
distribution. We show that the event distribution in the
vs. invariant mass-squared plane, where , are the transverse
energies of the two visible particles, contains the information of all three
invisible particle masses and allows them to be extracted individually. The
experimental smearing and combinatorial issues pose challenges to the mass
measurements. However, in many cases the three invisible particle masses in the
decay chain can be determined with reasonable accuracies.Comment: 45 pages, 32 figure
Almost-Commutative Geometries Beyond the Standard Model
In [7-9] and [10] the conjecture is presented that almost-commutative
geometries, with respect to sensible physical constraints, allow only the
standard model of particle physics and electro-strong models as
Yang-Mills-Higgs theories. In this publication a counter example will be given.
The corresponding almost-commutative geometry leads to a Yang-Mills-Higgs
model which consists of the standard model of particle physics and two new
fermions of opposite electro-magnetic charge. This is the second
Yang-Mills-Higgs model within noncommutative geometry, after the standard
model, which could be compatible with experiments. Combined to a hydrogen-like
composite particle these new particles provide a novel dark matter candidate
Constrained and reconstructing with semi-invisible production at hadron colliders
Mass variable \sqrt{\hat{S}_{min}} and its variants were constructed by
minimising the parton level center of mass energy that is consistent with all
inclusive measurements. They were proposed to have the ability to measure mass
scale of new physics in a fully model independent way. In this work we relax
the criteria by assuming the availability of partial informations of new
physics events and thus constraining this mass variable even further. Starting
with two different classes of production topology, i.e. antler and non-antler,
we demonstrate the usefulness of these variables to constrain the unknown
masses. This discussion is illustrated with different examples, from the
standard model Higgs production and beyond standard model resonance productions
leading to semi-invisible production. We also utilise these constrains to
reconstruct the semi-invisible events with the momenta of invisible particles
and thus improving the measurements to reveal the properties of new physics.Comment: v2: typos corrected, references added; Matches with published
version. 22 pages, 14 figure
Resolving Combinatorial Ambiguities in Dilepton Event Topologies with Constrained Variables
We advocate the use of on-shell constrained variables in order to
mitigate the combinatorial problem in SUSY-like events with two invisible
particles at the LHC. We show that in comparison to other approaches in the
literature, the constrained variables provide superior ansatze for the
unmeasured invisible momenta and therefore can be usefully applied to
discriminate combinatorial ambiguities. We illustrate our procedure with the
example of dilepton events. We critically review the existing
methods based on the Cambridge variable and MAOS-reconstruction of
invisible momenta, and show that their algorithm can be simplified without loss
of sensitivity, due to a perfect correlation between events with complex
solutions for the invisible momenta and events exhibiting a kinematic endpoint
violation. Then we demonstrate that the efficiency for selecting the correct
partition is further improved by utilizing the variables instead.
Finally, we also consider the general case when the underlying mass spectrum is
unknown, and no kinematic endpoint information is available
Polynomials, Riemann surfaces, and reconstructing missing-energy events
We consider the problem of reconstructing energies, momenta, and masses in
collider events with missing energy, along with the complications introduced by
combinatorial ambiguities and measurement errors. Typically, one reconstructs
more than one value and we show how the wrong values may be correlated with the
right ones. The problem has a natural formulation in terms of the theory of
Riemann surfaces. We discuss examples including top quark decays in the
Standard Model (relevant for top quark mass measurements and tests of spin
correlation), cascade decays in models of new physics containing dark matter
candidates, decays of third-generation leptoquarks in composite models of
electroweak symmetry breaking, and Higgs boson decay into two tau leptons.Comment: 28 pages, 6 figures; version accepted for publication, with
discussion of Higgs to tau tau deca
Expansion of the effective action around non-Gaussian theories
This paper derives the Feynman rules for the diagrammatic perturbation
expansion of the effective action around an arbitrary solvable problem. The
perturbation expansion around a Gaussian theory is well known and composed of
one-line irreducible diagrams only. For the expansions around an arbitrary,
non-Gaussian problem, we show that a more general class of irreducible diagrams
remains in addition to a second set of diagrams that has no analogue in the
Gaussian case. The effective action is central to field theory, in particular
to the study of phase transitions, symmetry breaking, effective equations of
motion, and renormalization. We exemplify the method on the Ising model, where
the effective action amounts to the Gibbs free energy, recovering the
Thouless-Anderson-Palmer mean-field theory in a fully diagrammatic derivation.
Higher order corrections follow with only minimal effort compared to existing
techniques. Our results show further that the Plefka expansion and the
high-temperature expansion are special cases of the general formalism presented
here.Comment: 37 pages, published versio
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