813 research outputs found
Flavor Physics in the Randall-Sundrum Model: I. Theoretical Setup and Electroweak Precision Tests
A complete discussion of tree-level flavor-changing effects in the
Randall-Sundrum (RS) model with brane-localized Higgs sector and bulk gauge and
matter fields is presented. The bulk equations of motion for the gauge and
fermion fields, supplemented by boundary conditions taking into account the
couplings to the Higgs sector, are solved exactly. For gauge fields the
Kaluza-Klein (KK) decomposition is performed in a covariant R_xi gauge. For
fermions the mixing between different generations is included in a completely
general way. The hierarchies observed in the fermion spectrum and the quark
mixing matrix are explained naturally in terms of anarchic five-dimensional
Yukawa matrices and wave-function overlap integrals. Detailed studies of the
flavor-changing couplings of the Higgs boson and of gauge bosons and their KK
excitations are performed, including in particular the couplings of the
standard W and Z bosons. A careful analysis of electroweak precision
observables including the S and T parameters and the Zbb couplings shows that
the simplest RS model containing only Standard Model particles and their KK
excitations is consistent with all experimental bounds for a KK scale as low as
a few TeV, if one allows for a heavy Higgs boson and/or for an ultra-violet
cutoff below the Planck scale. The study of flavor-changing effects includes
analyses of the non-unitarity of the quark mixing matrix, anomalous
right-handed couplings of the W bosons, tree-level flavor-changing neutral
current couplings of the Z and Higgs bosons, the rare decays t-->c(u)+Z and
t-->c(u)+h, and the flavor mixing among KK fermions. The results obtained in
this work form the basis for general calculations of flavor-changing processes
in the RS model and its extensions.Comment: 70 pages, 12 figures. v2: Incorrect treatment of phases in zero-mode
approximation corrected, and discussion of electroweak precision tests
modified. v3: Additional minor modifications and typos corrected; version
published in JHE
Axiflavon-Higgs Unification
In this talk, a unified model of scalar particles that addresses the flavour hierarchies, solves the strong CP problem, delivers a dark matter candidate, and radiatively triggers electroweak symmetry breaking is discussed. The recently proposed axiflavon is embedded together with an (elementary) Goldstone Higgs-sector in a single multiplet (and thereby also a model of flavour and strong CP conservation for the latter is provided). Bounds on the axion decay constant follow from requiring a SM-like Higgs potential at low energies and are confronted with constraints from flavour physics and astrophysics. In the minimal implementation, the axion decay constant is restricted to GeV, while adding right-handed neutrinos allows for a heavy-axion model at lower energies, down to TeV
Effect of magnetic field on the phase transition in a dusty plasma
The formation of self-consistent crystalline structure is a well-known
phenomenon in complex plasmas. In most experiments the pressure and rf power
are the main controlling parameters in determining the phase of the system. We
have studied the effect of externally applied magnetic field on the
configuration of plasma crystals, suspended in the sheath of a radio-frequency
discharge using the Magnetized Dusty Plasma Experiment (MDPX) device.
Experiments are performed at a fixed pressure and rf power where a crystalline
structure is formed within a confining ring. The magnetic field is then
increased from 0 to 1.28 T. We report on the breakdown of the crystalline
structure with increasing magnetic field. The magnetic field affects the
dynamics of the plasma particles and first leads to a rotation of the crystal.
At higher magnetic field, there is a radial variation (shear) in the angular
velocity of the moving particles which we believe leads to the melting of the
crystal. This melting is confirmed by evaluating the variation of the pair
correlation function as a function of magnetic field.Comment: 9 pages, 5 figure
Overvoltage characteristics in symmetrical monopolar HB MMC-HVDC configuration comprising long cable systems
This contribution focuses on high voltage direct current (HVDC) transmission systems comprising modular multilevel converters (MMC) equipped with half-bridge (HB) submodules and analyses cable voltage stresses during various station internal as well as dc side faults. In order to examine relevant overvoltage characteristics affecting HVDC cable systems, a systematic approach to evaluate overvoltage stresses is presented and an extensive set of time-domain simulations is analysed for schemes operating in symmetrical monopolar configuration. Obtained results are relevant for considerations on insulation co-ordination of HVDC cable systems and for a comprehensive definition of high voltage testing requirements
Model dependence of single-energy fits to pion photoproduction data
Model dependence of multipole analysis has been explored through
energy-dependent and single-energy fits to pion photoproduction data. The MAID
energy-dependent solution has been used as input for an event generator
producing realistic pseudo data. These were fitted using the SAID
parametrization approach to determine single-energy and energy-dependent
solutions over a range of lab photon energies from 200 to 1200 MeV. The
resulting solutions were found to be consistent with the input amplitudes from
MAID. Fits with a -squared per datum of unity or less were generally
achieved. We discuss energy regions where consistent results are expected, and
explore the sensitivity of fits to the number of included single- and
double-polarization observables. The influence of Watson's theorem is examined
in detail.Comment: 12 pages, 8 figure
Two loop electroweak corrections to and in the B-LSSM
The rare decays and are important to research new physics beyond standard model. In
this work, we investigate two loop electroweak corrections to and in the minimal
supersymmetric extension of the SM with local gauge symmetry (B-LSSM),
under a minimal flavor violating assumption for the soft breaking terms. In
this framework, new particles and new definition of squarks can affect the
theoretical predictions of these two processes, with respect to the MSSM.
Considering the constraints from updated experimental data, the numerical
results show that the B-LSSM can fit the experimental data for the branching
ratios of and . The
results of the rare decays also further constrain the parameter space of the
B-LSSM.Comment: 33 pages, 9 figures, Published in EPJ
Electroweak Constraints on Warped Geometry in Five Dimensions and Beyond
Here we consider the tree level corrections to electroweak (EW) observables
from standard model (SM) particles propagating in generic warped extra
dimensions. The scale of these corrections is found to be dominated by three
parameters, the Kaluza-Klein (KK) mass scale, the relative coupling of the KK
gauge fields to the Higgs and the relative coupling of the KK gauge fields to
fermion zero modes. It is found that 5D spaces that resolve the hierarchy
problem through warping typically have large gauge-Higgs coupling. It is also
found in where the additional dimensions are warped the relative
gauge-Higgs coupling scales as a function of the warp factor. If the warp
factor of the additional spaces is contracting towards the IR brane, both the
relative gauge-Higgs coupling and resulting EW corrections will be large.
Conversely EW constraints could be reduced by finding a space where the
additional dimension's warp factor is increasing towards the IR brane. We
demonstrate that the Klebanov Strassler solution belongs to the former of these
possibilities.Comment: 18 pages, 3 figures (references added) version to appear in JHE
The Custodial Randall-Sundrum Model: From Precision Tests to Higgs Physics
We reexamine the Randall-Sundrum (RS) model with enlarged gauge symmetry
SU(2)_L x SU(2)_R x U(1)_X x P_LR in the presence of a brane-localized Higgs
sector. In contrast to the existing literature, we perform the Kaluza-Klein
(KK) decomposition within the mass basis, which avoids the truncation of the KK
towers. Expanding the low-energy spectrum as well as the gauge couplings in
powers of the Higgs vacuum expectation value, we obtain analytic formulas which
allow for a deep understanding of the model-specific protection mechanisms of
the T parameter and the left-handed Z-boson couplings. In particular, in the
latter case we explain which contributions escape protection and identify them
with the irreducible sources of P_LR symmetry breaking. We furthermore show
explicitly that no protection mechanism is present in the charged-current
sector confirming existing model-independent findings. The main focus of the
phenomenological part of our work is a detailed discussion of Higgs-boson
couplings and their impact on physics at the CERN Large Hadron Collider. For
the first time, a complete one-loop calculation of all relevant Higgs-boson
production and decay channels is presented, incorporating the effects stemming
from the extended electroweak gauge-boson and fermion sectors.Comment: 74 pages, 13 figures, 3 tables. v2: Matches version published in JHE
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