262 research outputs found
Gluon Correlators in the Kogan-Kovner Model
The Lorentz-invariant gluon correlation functions, corresponding to scalar
and pseudo-scalar glueballs, are calculated for Kogan's and Kovner's
variational ansatz for the pure SU(N) Yang-Mills wavefunctional.
One expects that only one dynamical mass scale should be present in QCD; the
ansatz generates the expected scale for both glueballs, as well as an
additional scale for the scalar glueball. The additional mass scale must
therefore vanish, or be close to the expected one. This is shown to constrain
the nature of the phase transition in the Kogan-Kovner ansatz.Comment: 9 pages, no figure
Composite leptoquarks and anomalies in B-meson decays
We attempt to explain recent anomalies in semileptonic decays at LHCb via
a composite Higgs model, in which both the Higgs and an -triplet
leptoquark arise as pseudo-Goldstone bosons of the strong dynamics. Fermion
masses are assumed to be generated via the mechanism of partial compositeness,
which largely determines the leptoquark couplings and implies non-universal
lepton interactions. The latter are needed to accommodate tensions in the dataset and to be consistent with a discrepancy measured at LHCb
in the ratio of to branching
ratios. The data imply that the leptoquark should have a mass of around a TeV.
We find that the model is not in conflict with current flavour or direct
production bounds, but we identify a few observables for which the new physics
contributions are close to current limits and where the leptoquark is likely to
show up in future measurements. The leptoquark will be pair-produced at the LHC
and decay predominantly to third-generation quarks and leptons, and LHC13
searches will provide further strong bounds.This work has been partially supported by STFC grant ST/L000385/1 and King's College, Cambridge.This is the final published version. It first appeared at http://dx.doi.org/10.1007/JHEP05(2015)00
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
Improved variational analysis of deconfinement in SU(N) gauge theory
A variational analysis of the pure SU(N) gauge theory in 3+1 dimensions at finite temperature is performed, extending the work of Kogan, Kovner and Milhano in hep-ph/0208053 . A de-confining phase transition is found at a temperature of 470 MeV, somewhat higher than lattice estimates. This value is however rather sensitive, for reasons which are discussed. A more robust quantity is the ratio of the transition temperature to the lightest glueball mass in the model. This is 0.18, in agreement with the lattice estimate for SU(3) to two significant figures. Ways of further improving the calculation are discussed
Nambu-Goldstone Modes in Gravitational Theories with Spontaneous Lorentz Breaking
Spontaneous breaking of Lorentz symmetry has been suggested as a possible
mechanism that might occur in the context of a fundamental Planck-scale theory,
such as string theory or a quantum theory of gravity. However, if Lorentz
symmetry is spontaneously broken, two sets of questions immediately arise: what
is the fate of the Nambu-Goldstone modes, and can a Higgs mechanism occur? A
brief summary of some recent work looking at these questions is presented here.Comment: 6 pages. Presented at the meeting "From Quantum to Cosmos,"
Washington, D.C., May 2006; published in Int. J. Mod. Phys. D16:2357-2363,
200
The Three Dimensional Dual of 4D Chirality
Chiral gauge theories can be defined in four-dimensional Anti de Sitter
space, but AdS boundary conditions explicitly break the chiral symmetry in a
specific, well defined manner, which in turns results in an anomalous Ward
identity. When the 4D theory admits a dual description in terms of a 3D CFT,
the 3D dual of the broken chiral symmetry is a certain double-trace deformation
of the CFT, which produces the same anomalous chiral Ward identities that
obtains in the 4D bulk theory.Comment: 10 pages, small misprints corrected, reference [16] updated. Version
to appear in JHE
Gauge Boson Mass Generation in AdS4
We investigate the role of boundary conditions in gauge theories in AdS4. The
presence of the boundary can break the gauge symmetry consistently with AdS4
isometries. We show that, as a consequence, the gauge bosons associated to the
broken symmetries become massive at one loop. In particular chiral gauge
theories such us the Standard Model are necessarily massive in AdS4. We briefly
discuss similarities with the Schwinger model and implications for CFTs in
three dimensions.Comment: 12 page
Transverse mass and invariant mass observables for measuring the mass of a semi-invisibly decaying heavy particle
Formulae are derived for the positions of end-points in the invariant mass
and transverse mass distributions obtained from the products of heavy states
decaying to pairs of semi-invisibly decaying lighter states. Formulae are
derived both for the special case where the two decay chains are identical and
the more general case where they are different. The formulae are tested with a
simple case study of heavy SUSY higgs particles decaying to gauginos at the
LHC.Comment: 13 pages, 8 eps figure
A hybrid method for determining particle masses at the Large Hadron Collider with fully identified cascade decays
A new technique for improving the precision of measurements of SUSY particle
masses at the LHC is introduced. The technique involves kinematic fitting of
events with two fully identified decay chains. We incorporate both event ETmiss
constraints and independent constraints provided by kinematic end-points in
experiment invariant mass distributions of SUSY decay products. Incorporation
of the event specific information maximises the information used in the fit and
is shown to reduce the mass measurement uncertainites by ~30% compared to
conventional fitting of experiment end-point constraints for the SPS1a
benchmark model.Comment: 10 pages, 2 .eps figures, JHEP3 styl
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