89 research outputs found
Realistic GUT Yukawa Couplings from a Random Clockwork Model
We present realistic models of flavor in SU(5) and SO(10) grand unified
theories (GUTs). The models are renormalizable and do not require any exotic
representations in order to accommodate the necessary GUT breaking effects in
the Yukawa couplings. They are based on a simple clockwork Lagrangian whose
structure is enforced with just two (one) vectorlike U(1) symmetries in the
case of SU(5) and SO(10) respectively. The inter-generational hierarchies arise
spontaneously from products of matrices with order one random entries.Comment: 18 pages, 2 figure
Natural Fermion Hierarchies from Random Yukawa Couplings
The Standard Model of particle physics requires Yukawa matrices with
eigenval- ues that differ by orders of magnitude. We propose a novel way to
explain this fact without any small or large parameters. The mechanism is based
on the observation that products of matrices of random order one-numbers have
hierarchical spectra. The same mechanism can easily account for the
hierarchical structure of the quark mixing matrix.Comment: 9 pages. v2: Extended and improved discussion on CKM matrix.
References added. Matches published versio
One-Loop Effective Action in Orbifold Compactifications
We employ the covariant background formalism to derive generic expressions
for the one-loop effective action in field theoretic orbifold
compactifications. The contribution of each orbifold sector is given by the
effective action of its fixed torus with a shifted mass matrix. We thus study
in detail the computation of the heat kernel on tori. Our formalism manifestly
separates UV sensitive (local) from UV-insensitive (nonlocal) renormalization.
To exemplify our methods, we study the effective potential of 6d gauge theory
as well as kinetic terms for gravitational moduli in 11d supergravity.Comment: 30 pages, 1 figure, 3 tables, v2: appendix on zeta function
regularization added, discussion of 6d example expanded, version to appear in
JHE
Effective theory for neutral resonances and a statistical dissection of the ATLAS diboson excess
We classify the complete set of dimension-5 operators relevant for the
resonant production of a singlet of spin 0 or 2 linearly coupled to the
Standard Model (SM). We compute the decay width of such states as a function of
the effective couplings, and provide the matching to various well-motivated New
Physics scenarios. We then investigate the possibility that one of these
neutral resonances be at the origin of the excess in diboson production
recently reported by the ATLAS collaboration. We perform a shape analysis of
the excess under full consideration of the systematic uncertainties to extract
the width of the hypothetical resonance, finding it to be in
the range 26 GeV 144 GeV at 95\% C.L. We then point out
that the three overlapping selections , , reported by ATLAS follow
a joint trivariate Poisson distribution, which opens the possibility of a
thorough likelihood analysis of the event rates. The background systematic
uncertainties are also included in our analysis. We show that the data do not
require production and could thus in principle be explained by neutral
resonances. We then use both the information on the width and the cross
section, which prove to be highly complementary, to test the effective
Lagrangians of singlet resonances. Regarding specific models, we find that
neither scalars coupled via the Higgs-portal nor the Randall-Sundrum (RS)
radion can explain the ATLAS anomaly. The RS graviton with all matter on the
infrared (IR) brane can in principle fit the observed excess, while the RS
model with matter propagating in the bulk requires the presence of IR brane
kinetic terms for the gauge fields.Comment: 31 page
Anomalous gauge couplings from composite Higgs and warped extra dimensions
We examine trilinear and quartic anomalous gauge couplings (AGCs) generated
in composite Higgs models and models with warped extra dimensions. We first
revisit the SU(2)_L x U(1)_Y effective Lagrangian and derive the charged and
two-photon neutral AGCs. We derive the general perturbative contributions to
the pure field-strength operators from spin 0, 1/2, 1 resonances by means of
the heat kernel method. In the composite Higgs framework, we derive the pattern
of expected deviations from typical SO(N) embeddings of the light composite top
partner. We then study a generic warped extra dimension framework with AdS_5
background, recasting in few parameters the features of models relevant for
AGCs. We also present a detailed study of the latest bounds from electroweak
and Higgs precision observables, with and without brane kinetic terms. For
vanishing brane kinetic terms, we find that the S and T parameters exclude KK
gauge modes of the RS custodial [non-custodial] scenario below 7.7 [14.7] TeV,
for a brane Higgs and below 6.6 [8.1] TeV for a Pseudo Nambu-Goldstone Higgs,
at 95% CL. These constraints can be relaxed in presence of brane kinetic terms.
The leading AGCs are probing the KK gravitons and the KK modes of bulk gauge
fields in parts of the parameter space. In these scenarios, the future CMS and
ATLAS forward proton detectors could be sensitive to the effect of KK gravitons
in the multi-TeV mass range.Comment: 37 pages, 2 figures, 3 tables. Minor typos fixed, some comments and
references added. Matches JHEP versio
Factorization of covariant Feynman graphs for the effective action
We prove a neat factorization property of Feynman graphs in covariant
perturbation theory. The contribution of the graph to the effective action is
written as a product of a massless scalar momentum integral that only depends
on the basic graph topology, and a background-field dependent piece that
contains all the information of spin, gauge representations, masses etc. We
give a closed expression for the momentum integral in terms of four graph
polynomials whose properties we derive in some detail. Our results can also be
useful for standard (non-covariant) perturbation theory
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