2,340 research outputs found
Inertial Spontaneous Symmetry Breaking and Quantum Scale Invariance
Weyl invariant theories of scalars and gravity can generate all mass scales
spontaneously, initiated by a dynamical process of "inertial spontaneous
symmetry breaking" that does not involve a potential. This is dictated by the
structure of the Weyl current, , and a cosmological phase during which
the universe expands and the Einstein-Hilbert effective action is formed.
Maintaining exact Weyl invariance in the renormalised quantum theory is
straightforward when renormalisation conditions are referred back to the VEV's
of fields in the action of the theory, which implies a conserved Weyl current.
We do not require scale invariant regulators. We illustrate the computation of
a Weyl invariant Coleman-Weinberg potential
An ultra-weak sector, the strong CP problem and the pseudo-Goldstone dilaton
In the context of a Coleman-Weinberg mechanism for the Higgs boson mass, we
address the strong CP problem. We show that a DFSZ-like invisible axion model
with a gauge-singlet complex scalar field S, whose couplings to the Standard
Model are naturally ultra-weak, can solve the strong CP problem and
simultaneously generate acceptable electroweak symmetry breaking. The
ultra-weak couplings of the singlet S are associated with underlying
approximate shift symmetries that act as custodial symmetries and maintain
technical naturalness. The model also contains a very light pseudo-Goldstone
dilaton that is consistent with cosmological Polonyi bounds, and the axion can
be the dark matter of the universe. We further outline how a SUSY version of
this model, which may be required in the context of Grand Unification, can
avoid introducing a hierarchy problem.Comment: 9 page
Hybrid Natural Inflation
We construct two simple effective field theory versions of {\it Hybrid
Natural Inflation (HNI)} that illustrate the range of its phenomenological
implications. The resulting inflationary sector potential,
, arises naturally, with the inflaton field a
pseudo-Nambu-Goldstone boson. The end of inflation is triggered by a waterfall
field and the conditions for this to happen are determined. Also of interest is
the fact that the slow-roll parameter (and hence the tensor ) is
a non-monotonic function of the field with a maximum where observables take
universal values that determines the maximum possible tensor to scalar ratio
. In one of the models the inflationary scale can be as low as the
electroweak scale. We explore in detail the associated HNI phenomenology,
taking account of the constraints from Black Hole production, and perform a
detailed fit to the Planck 2015 temperature and polarisation data.Comment: V2: 19 pages, 2 figures, 1 table. Extended discussions and new
references added. Version accepted for publication in JHE
Ultra-weak sector, Higgs boson mass, and the dilaton
The Higgs boson mass may arise from a portal coupling to a singlet field
which has a very large VEV . This requires a
sector of "ultra-weak" couplings , where . Ultra-weak couplings are technically naturally small
due to a custodial shift symmetry of in the
limit. The singlet field has properties similar to a pseudo-dilaton.
We engineer explicit breaking of scale invariance in the ultra-weak sector via
a Coleman-Weinberg potential, which requires hierarchies amongst the ultra-weak
couplings.Comment: 6 page
Beyond the Standard Model
The attempts to develop models beyond the Standard Model are briefly reviewed paying particular regard to the mechanisms responsible for symmetry breaking and mass generation. A comparison is made of the theoretical expectations with recent precision measurements for theories with composite Higgs and for supersymmetric theories with elementary Higgs boson(s). The implications of a heavy top quark and the origin of the light quark and lepton masses and mixing angles are considered within these frameworks
The kaon nucleon interaction
The K-matrix formalism for the low energy KN interaction is reviewed. By using the N/D method to compute the scattering matrix for left hand singularities chosen to approximate the physical singularities of the KN and ΣΤ amplitudes the nature of the energy dependence of the inverse K-matrix elements are investigated. From this it is concluded that an effective range parameterisation should be a good approximation to the inverse K-matrix elements and that the off diagonal elements of the effective range matrix may not, ά priori, be neglected. The application of dispersion relations to the prediction of the strange particle coupling constants is discussed. A once subtracted sum rule is introduced which reduces the discrepancy in the prediction of the coupling constants due to the use of different low energy parameterisations for the KN amplitude. The resultant prediction of the coupling constants is incompatible with the SU(3) predictions. A new S-wave zero range fit to the low energy KN data is performed. A good fit is obtained which improves on previous analyses over the low energy KN region. The values of the coupling constants predicted by the standard dispersion relation using this parameterisation are again incompatible with the SU(3) predictions. Finally the effect of the non-negligible P waves in the isospin one channel are investigated using a constant scattering length parameterisation for these waves in the analysis of the low energy KN data
Neutrino Masses and Mixing in Brane-World Theories
We present a comprehensive study of five-dimensional brane-world models for
neutrino physics based on flat compactifications. Particular emphasis is put on
the inclusion of bulk mass terms. We derive a number of general results for
such brane-world models with bulk mass terms. In particular, in the limit of
small brane-bulk couplings, the electroweak eigenstates are predominantly given
as a superposition of three light states with non-trivial small admixtures of
bulk states. As a consequence, neutrinos can undergo standard oscillations as
well as oscillation into bulk Kaluza-Klein states. We use this structure to
construct a specific model based on Z_2 orbifolding and bulk Majorana masses
which is compatible with all observed oscillation phenomena. The solar neutrino
deficit is explained by oscillations into sterile bulk states while the
atmospheric neutrino deficit is due to mu - tau oscillations with naturally
maximal mixing. In addition, the model can accommodate the LSND result and a
significant neutrino dark matter component. We also analyze the constraints
from supernova energy loss on neutrino brane-world theories and show that our
specific model is consistent with these constraints.Comment: 45 pages, Latex, 1 eps-figur
Inflation in a scale invariant universe
A scale-invariant universe can have a period of accelerated expansion at
early times: inflation. We use a frame-invariant approach to calculate
inflationary observables in a scale invariant theory of gravity involving two
scalar fields - the spectral indices, the tensor to scalar ratio, the level of
isocurvature modes and non-Gaussianity. We show that scale symmetry leads to an
exact cancellation of isocurvature modes and that, in the scale-symmetry broken
phase, this theory is well described by a single scalar field theory. We find
the predictions of this theory strongly compatible with current observations.Comment: 9 pages, 2 figures; v2: minor clarifications added, matches published
versio
The Precision Determination of Invisible-Particle Masses at the LHC
We develop techniques to determine the mass scale of invisible particles
pair-produced at hadron colliders. We employ the constrained mass variable
m_2C, which provides an event-by-event lower-bound to the mass scale given a
mass difference. We complement this variable with a new variable m_2C,UB which
provides an additional upper bound to the mass scale, and demonstrate its
utility with a realistic case study of a supersymmetry model. These variables
together effectively quantify the `kink' in the function Max m_T2 which has
been proposed as a mass-determination technique for collider-produced dark
matter. An important advantage of the m_2C method is that it does not rely
simply on the position at the endpoint, but it uses the additional information
contained in events which lie far from the endpoint. We found the mass by
comparing the HERWIG generated m_2C distribution to ideal distributions for
different masses. We find that for the case studied, with 100 fb^-1 of
integrated luminosity (about 400 signal events), the invisible particle's mass
can be measured to a precision of 4.1 GeV. We conclude that this technique's
precision and accuracy is as good as, if not better than, the best known
techniques for invisible-particle mass-determination at hadron colliders.Comment: 20 pages, 11 figures, minor correction
Multi-Brane Worlds and modification of gravity at large scales
We discuss the implications of multi-brane constructions involving
combinations of positive and negative tension brane and show how anomalously
light KK states emerge when negative tension ''-'' branes are sandwiched
between ''+'' branes. We present a detailed study of a ''+--+'' brane
assignment which interpolates between two models that have been previously
proposed in which gravity is modified at large scales due to the anomalously
light states. We show that it has the peculiar characteristic that gravity
changes from four dimensional (4D) to 5D at large distances and returns to 4D
at even larger scales. We also consider a crystalline universe which leads to a
similar structure for gravity. The problems associated with intermediate
negative tension branes are discussed and a possible resolution suggested.Comment: 28 pages, 6 figures,references adde
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