1,547 research outputs found
Discrete regularisation of localised kinetic terms
We investigate the behaviour of 5d models with general brane kinetic terms by
discretising the extra dimension. We show that in the continuum limit the
Kaluza-Klein masses and wave functions are in general nonanalytic in the
coefficients of brane terms.Comment: Presented at the 7th DESY Workshop on Elementary Particle Theory
``Loops and Legs in Quantum Field Theory'', Zinnowitz, April 25-30, 200
Gauge coupling renormalization in RS1
We compute the 4D low energy effective gauge coupling at one-loop order in
the compact Randall-Sundrum scenario with bulk gauge fields and charged matter,
within controlled approximations. While such computations are subtle, they can
be important for studying phenomenological issues such as grand unification.
Ultraviolet divergences are cut-off using Pauli-Villars regularization so as to
respect 5D gauge and general coordinate invariance. The structure of these
divergences on branes and in the bulk is elucidated by a 5D position-space
analysis. The remaining finite contributions are obtained by a careful analysis
of the Kaluza-Klein spectrum. We comment on the agreement between our results
and expectations based on the AdS/CFT correspondence, in particular logarithmic
sensitivity to the 4D Planck scale.Comment: 17 pages, Latex2e, uses axodraw.sty, new references added. To be
published in Nucl. Phys.
6D Higgsless Standard Model
We present a 6D Higgsless Standard Model with a realistic gauge sector. The
model uses only the Standard Model gauge group SU(2)xU(1) with the gauge bosons
propagating in flat extra dimensions which are compactified on a rectangle. The
electroweak symmetry is broken by boundary conditions, and the correct
splitting between the W and Z boson masses can be arranged by a suitable choice
of the compactification scales. The higher Kaluza-Klein excitations of the
gauge bosons decouple from the low-energy theory due to dominant brane kinetic
terms. The model has the following two key features compared to 5D models. The
bulk kinetic couplings, responsible for electroweak symmetry breaking using
mixed boundary conditions, are of order the electroweak scale. Moreover, the
agreement with the precision electroweak parameters is improved compared to 5D
warped or flat models. We also argue that the calculability of Higgsless models
can be ameliorated in more than five dimensions.Comment: 15 pages, 3 figures, discussion of fermion masses added, comment on
scalar degrees of freedom included, references adde
Grand Unification in RS1
We study unification in the Randall-Sundrum scenario for solving the
hierarchy problem, with gauge fields and fermions in the bulk. We calculate the
one-loop corrected low-energy effective gauge couplings in a unified theory,
broken at the scale M_GUT in the bulk. We find that, although this scenario has
an extra dimension, there is a robust (calculable in the effective field
theory) logarithmic dependence on M_GUT, strongly suggestive of high-scale
unification, very much as in the (4D) Standard Model. Moreover, bulk threshold
effects are naturally small, but volume-enhanced, so that we can accommodate
the measured gauge couplings. We show in detail how excessive proton decay is
forbidden by an extra U(1) bulk gauge symmetry. This mechanism requires us to
further break the unified group using boundary conditions. A 4D dual
interpretation, in the sense of the AdS/CFT correspondence, is provided for all
our results. Our results show that an attractive unification mechanism can
combine with a non-supersymmetric solution to the hierarchy problem.Comment: Latex, 23 pages. In the revised version, Eq. (3.3) has been modified
with no change in the central result of the paper and a reference has been
adde
Shaping the top asymmetry
We study different profiles of the distribution of the top forward-backward
asymmetry, depending on the invariant mass of the t tbar pair. We show that
they can be reproduced by one or more light colour octets, while keeping
moderate departures of the t tbar cross section and invariant mass
distributions with respect to the Standard Model predictions at Tevatron and
LHC.Comment: LaTeX 14 pages. Final version to appear in PLB, with an enlarged
discussion about dijet constraint
Vector Bosons in the Randall-Sundrum 2 and Lykken-Randall models and unparticles
Unparticle behavior is shown to be realized in the Randall-Sundrum 2 (RS 2)
and the Lykken-Randall (LR) brane scenarios when brane-localized Standard Model
currents are coupled to a massive vector field living in the five-dimensional
warped background of the RS 2 model. By the AdS/CFT dictionary these
backgrounds exhibit certain properties of the unparticle CFT at large N_c and
strong 't Hooft coupling. Within the RS 2 model we also examine and contrast in
detail the scalar and vector position-space correlators at intermediate and
large distances. Unitarity of brane-to-brane scattering amplitudes is seen to
imply a necessary and sufficient condition on the positivity of the bulk mass,
which leads to the well-known unitarity bound on vector operators in a CFT.Comment: 60 pages, 8 figure
Probe dependency in the determination of ligand binding kinetics at a prototypical G protein-coupled receptor
© 2019, The Author(s). Drug-target binding kinetics are suggested to be important parameters for the prediction of in vivo drug-efficacy. For G protein-coupled receptors (GPCRs), the binding kinetics of ligands are typically determined using association binding experiments in competition with radiolabelled probes, followed by analysis with the widely used competitive binding kinetics theory developed by Motulsky and Mahan. Despite this, the influence of the radioligand binding kinetics on the kinetic parameters derived for the ligands tested is often overlooked. To address this, binding rate constants for a series of histamine H1 receptor (H1R) antagonists were determined using radioligands with either slow (low koff) or fast (high koff) dissociation characteristics. A correlation was observed between the probe-specific datasets for the kinetic binding affinities, association rate constants and dissociation rate constants. However, the magnitude and accuracy of the binding rate constant-values was highly dependent on the used radioligand probe. Further analysis using recently developed fluorescent binding methods corroborates the finding that the Motulsky-Mahan methodology is limited by the employed assay conditions. The presented data suggest that kinetic parameters of GPCR ligands depend largely on the characteristics of the probe used and results should therefore be viewed within the experimental context and limitations of the applied methodology
Symmetry preserving regularization with a cutoff
A Lorentz and gauge symmetry preserving regularization method is proposed in
4 dimension based on momentum cutoff. We use the conditions of gauge invariance
or freedom of shift of the loop-momentum to define the evaluation of the terms
carrying Lorentz indices, e.g. proportional to k_{\mu}k_{\nu}. The remaining
scalar integrals are calculated with a four dimensional momentum cutoff. The
finite terms (independent of the cutoff) are unambiguous and agree with the
result of dimensional regularization.Comment: 12 pages, 1 figure, v2 references adde
Warped Supersymmetric Grand Unification
We construct a realistic theory of grand unification in AdS_5 truncated by
branes, in which the unified gauge symmetry is broken by boundary conditions
and the electroweak scale is generated by the AdS warp factor. We show that the
theory preserves the successful gauge coupling unification of the 4D MSSM at
leading-logarithmic level. Kaluza-Klein (KK) towers, including those of XY
gauge and colored Higgs multiplets, appear at the TeV scale, while the extra
dimension provides natural mechanisms for doublet-triplet splitting and proton
decay suppression. In one possible scenario supersymmetry is strongly broken on
the TeV brane, in which case the lightest SU(3)_C x SU(2)_L x U(1)_Y gauginos
are approximately Dirac and the mass of the lightest XY gaugino is pushed well
below that of the lowest gauge boson KK mode, improving the prospects for its
production at the LHC. The bulk Lagrangian possesses a symmetry that we call
GUT parity. If GUT parity is exact, the lightest GUT particle, most likely an
XY gaugino, is stable. Once produced in a collider, the XY gaugino hadronizes
to form mesons, some of which will be charged and visible as highly ionizing
tracks. The lightest supersymmetric particle is the gravitino of mass \sim
10^{-3} eV, which is also stable if R parity is conserved.Comment: 41 pages, LaTeX, version to appear in Phys. Rev.
RS1, Custodial Isospin and Precision Tests
We study precision electroweak constraints within a RS1 model with gauge
fields and fermions in the bulk. The electroweak gauge symmetry is enhanced to
SU(2)_L \times SU(2)_R \times U(1)_{B-L}, thereby providing a custodial isospin
symmetry sufficient to suppress excessive contributions to the T parameter. We
then construct complete models, complying with all electroweak constraints, for
solving the hierarchy problem, without supersymmetry or large hierarchies in
the fundamental couplings. Using the AdS/CFT correspondence our models can be
interpreted as dual to a strongly coupled conformal Higgs sector with global
custodial symmetry, gauge and fermionic matter being fundamental fields
external to the CFT. This scenario has interesting collider signals, distinct
from other RS models in the literature.Comment: 32 pages, 6 figures, latex2e, minor changes, references adde
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