70 research outputs found
Probing Compositeness with the CMS & Data
Quark-lepton compositeness is a well-known beyond the Standard Model (SM)
scenario with heavy exotic particles like leptoquarks (LQs) and leptogluons
(LGs) etc. These particles can couple to leptons and jets simultaneously. In
this letter, we use the recent CMS scalar LQ search data in the and
channels to probe this scenario. We recast the data in terms of a color
octet partner of the SM electron (or a first generation spin-1/2 LG) that
couples to an electron and a gluon via a dimension five operator suppressed by
the quark-lepton compositeness scale (). By combining different
production processes of the color octet electron () at the LHC, we use the
CMS 8TeV data to obtain a simultaneous bound on and the mass of the
(). We also study the reach of the 13 TeV LHC to discover the
and interpret the required luminosity in terms of and
.Comment: 7 pages, 6 figures, 3 tables. Minor changes, typos fixed. Matches
with the published versio
On a boundary-localized Higgs boson in 5D theories
In the context of a simple five-dimensional (5D) model with bulk matter
coupled to a brane-localized Higgs boson, we point out a new non-commutativity
in the 4D calculation of the mass spectrum for excited fermion towers: the
obtained expression depends on the choice in ordering the limits, N->infinity
(infinite Kaluza-Klein tower) and epsilon->0 (epsilon being the parameter
introduced for regularizing the Higgs Dirac peak). This introduces the physical
question of which one is the correct order; we then show that the two possible
orders of regularization (called I and II) are physically equivalent, as both
can typically reproduce the measured observables, but that the one with less
degrees of freedom (I) could be uniquely excluded by future experimental
constraints. This conclusion is based on the exact matching between the 4D and
5D analytical calculations of the mass spectrum - via the regularizations of
type I and II. Beyond a deeper insight into the Higgs peak regularizations,
this matching also allows us to confirm the validity of the usual 5D
mixed-formalism and to clarify the UV cut-off procedure. All the conclusions,
deduced from regularizing the Higgs peak through a brane shift or a smoothed
square profile, are expected to remain similar in realistic models with a
warped extra-dimension.Comment: 29 pages, 2 table
Effect of Anomalous Couplings on the Associated Production of a Single Top Quark and a Higgs Boson at the LHC
We consider the production of a single top quark in association with a Higgs
boson at the LHC. In particular, we compute the cross sections for the
processes , , , , , ,
in the presence of the anomalous and couplings. We
find that the anomalous and couplings can enhance the cross
sections significantly. We also analyze a few signatures and show that, if
these couplings are indeed anomalous, then with enough data, one should be able
to observe the production of the Higgs boson in association with single top
quark.Comment: 15 pages, 4 figures, 5 tables. Typos fixed, reference added. Journal
versio
Single Productions of Colored Particles at the LHC: An Example with Scalar Leptoquarks
Current LHC searches for new colored particles generally focus on their pair
production channels and assume any single production to be negligible. We argue
that such an assumption may be unnecessary in some cases. Inclusion of model
dependent single productions in pair production searches (or vice versa) can
give us new information about model parameters or better exclusion limits.
Considering the example of the recent CMS search for first generation scalar
leptoquarks in the pair production channel, we illustrate how single
productions can be systematically included in the signal estimations and
demonstrate how it can affect the mass exclusion limits and give new bounds on
leptoquark-lepton-quark couplings. We also estimate the effect of the pair
production in the more recent CMS search for scalar leptoquarks in single
production channels.Comment: 11 pages, 6 figures, 2 tables. References added. Comments added on LQ
single production search by CMS. Journal versio
Scale Invariance as a Solution to the Cosmological Constant Problem
We show that scale invariance provides a solution to the fine tuning problem
of the cosmological constant. We construct a generalization of the standard
model of particle physics which displays exact quantum scale invariance. The
matter action is invariant under global scale transformations in arbitrary
dimensions. However the gravitational action breaks scale invariance
explicitly. The scale symmetry is broken spontaneously in the matter sector of
the theory. We show that the contribution to the vacuum energy and hence the
cosmological constant is identically zero from the matter sector within the
full quantum theory. However the gravitational sector may give non-zero
contributions to the cosmological constant at loop orders. No fine tuning may
be required at loop orders since the matter sector gives zero contribution to
the cosmological constant. We also show that we do not require full scale
invariance in order to constrain the vacuum energy from the matter sector. We
only require invariance under pseudoscale transformations. Using this idea and
motivated by the concept of unimodular gravity we propose an alternative model.
In this case also we show that matter sector gives exactly zero contribution to
the vacuum energy.Comment: 12 pages, no figure
- …