6,106 research outputs found

### Ultraviolet Properties of the Higgs Sector in the Lee-Wick Standard Model

The Lee-Wick (LW) Standard Model (SM) offers a new solution to the hierarchy
problem. We discuss, using effective potential techniques, its peculiar
ultraviolet (UV) behaviour. We show how quadratic divergences in the Higgs mass
Mh cancel as a result of the unusual dependence of LW fields on the Higgs
background (in a manner reminiscent of Little Higgses). We then extract from
the effective potential the renormalization group evolution of the Higgs
quartic coupling lambda above the LW scale. After clarifying an apparent
discrepancy with previous results for the LW Abelian Higgs model we focus on
the LWSM. In contrast with the SM case, for any Mh, lambda grows monotonically
and hits a Landau pole at a fixed trans-Planckian scale (never turning negative
in the UV). Then, the perturbativity and stability bounds on Mh disappear. We
identify a cutoff ~10^{16} GeV for the LWSM due to the hypercharge gauge
coupling hitting a Landau pole. Finally, we also discuss briefly the possible
impact of the UV properties of the LW models on their behaviour at finite
temperature, in particular regarding symmetry nonrestoration.Comment: 25 pages, 3 figure

### Lepton non-universality in $B$ decays and fermion mass structure

We consider the possibility that the neutral-current $B$ anomalies are due to
radiative corrections generated by Yukawa interactions of quarks and leptons
with new vector-like quark and lepton electroweak doublets and new Standard
Model singlet scalars. We show that the restricted interactions needed can
result from an underlying Abelian family symmetry and that the same symmetry
can give rise to an acceptable pattern of quark and charged lepton masses and
mixings, providing a bridge between the non-universality observed in the
B-sector and that of the fermion mass matrices. We construct two simple models,
one with a single singlet scalar in which the flavour changing comes from quark
and lepton mixing and one with an additional scalar in which the flavour
changing can come from both fermion and scalar mixing. We show that for the
case the new quarks are much heavier than the new leptons and scalars the $B$
anomalies can be due to box diagrams with couplings in the perturbative regime
consistent with the bounds coming from $B_s- \bar B_s$, $K- \bar K$ and $D-
\bar D$ mixing as well as other lepton family number violating processes. The
new states can be dark matter candidates and, in the two scalar model with a
light scalar of O(60) GeV and vector-like lepton of O(100) GeV, there can be a
simultaneous explanation of the B-anomalies, the muon anomalous magnetic moment
and the dark matter abundance.Comment: Replacement contains few additional reference

### Heavy Meson Physics: What have we learned in Twenty Years?

I give a personal account of the development of the field of heavy quarks.
After reviewing the experimental discovery of charm and bottom quarks, I
describe how the field's focus shifted towards determination of CKM elements
and how this has matured into a precision science.Comment: This talk was presented during the ceremony awarding the Medalla 2003
of the Division of Particles and Fields of The Mexican Phsyical Society, at
the IX Mexican Workshop on Particles and Fields; submitted for proceedings; 9
pages, 9 figures; replacement: fix multiple typo

### Magnetic Wormholes and Vertex Operators

We consider wormhole solutions in $2+1$ Euclidean dimensions. A duality
transformation is introduced to derive a new action from magnetic wormhole
action of Gupta, Hughes, Preskill and Wise. The classical solution is
presented. The vertex operators corresponding to the wormhole are derived.
Conformally coupled scalars and spinors are considered in the wormhole
background and the vertex operators are computed. ( To be published in Phys.
Rev. D15)Comment: 18 pages of RevTex, preprint IP/BBSR/94-2

### Massive Vector Scattering in Lee-Wick Gauge Theory

We demonstrate that amplitudes describing scattering of longitudinally
polarized massive vector bosons present in non-Abelian Lee-Wick gauge theory do
not grow with energy and, hence, satisfy the constraints imposed by
perturbative unitarity. This result contrasts with the widely-known violation
of perturbative unitarity in the standard model with a very heavy Higgs. Our
conclusions are valid to all orders of perturbation theory and depend on the
existence of a formulation of the theory in which all operators are of
dimension four or less. This can be thought of as a restriction on the kinds of
higher dimension operator which can be included in the higher derivative
formulation of the theory.Comment: 11 pages, no figure

### Quantum phase transitions of the diluted O(3) rotor model

We study the phase diagram and the quantum phase transitions of a
site-diluted two-dimensional O(3) quantum rotor model by means of large-scale
Monte-Carlo simulations. This system has two quantum phase transitions, a
generic one for small dilutions, and a percolation transition across the
lattice percolation threshold. We determine the critical behavior for both
transitions and for the multicritical point that separates them. In contrast to
the exotic scaling scenarios found in other random quantum systems, all these
transitions are characterized by finite-disorder fixed points with power-law
scaling. We relate our findings to a recent classification of phase transitions
with quenched disorder according to the rare region dimensionality, and we
discuss experiments in disordered quantum magnets.Comment: 11 pages, 14 eps figures, final version as publishe

### Non-factorizable contributions to $\bar{B^0_d} \to D_s^{(*)} \bar{D_s^{(*)}}$

It is pointed out that decays of the type $B \to D \bar{D}$ have no
factorizable contributions, unless at least one of the charmed mesons in the
final state is a vector meson. The dominant contributions to the decay
amplitudes arise from chiral loop contributions and tree level amplitudes
generated by soft gluon emissions forming a gluon condensate. We predict that
the branching ratios for the processes $\bar B^0 \to D_s^+ D_s^-$,
$\bar B^0 \to D_s^{+*} D_s^-$ and $\bar B^0 \to D_s^+ D_s^{-*}$ are all of
order $(3- 4) \times 10^{-4}$, while $\bar B^0 \to D_s^{+*} D_s^{-*}$ has a
branching ratio 5 to 10 times bigger. We emphasize that the branching ratios
are sensitive to $1/m_c$ corrections.Comment: 4 pages, 4 figures. Based on talk by J.O. Eeg at BEACH 2004, 6th
international conference on Hyperons, Charm and Beauty Hadrons, Illionois
Institute of Technology, Chicago, june. 27 - july 3, 200

### Scaling behavior of the absorbing phase transition in a conserved lattice gas around the upper critical dimension

We analyse numerically the critical behavior of a conserved lattice gas which
was recently introduced as an example of the new universality class of
absorbing phase transitions with a conserved field [Phys. Rev. Lett. 85, 1803
(2000)]. We determine the critical exponent of the order parameter as well as
the critical exponent of the order parameter fluctuations in D=2,3,4,5
dimensions. A comparison of our results and those obtained from a mean-field
approach and a field theory suggests that the upper critical dimension of the
absorbing phase transition is four.Comment: 5 pages, 11 figure

### Radiation hardness of small-pitch 3D pixel sensors up to HL-LHC fluences

A new generation of 3D silicon pixel detectors with a small pixel size of
50$\times$50 and 25$\times$100 $\mu$m$^{2}$ is being developed for the HL-LHC
tracker upgrades. The radiation hardness of such detectors was studied in beam
tests after irradiation to HL-LHC fluences up to $1.4\times10^{16}$
n$_{\mathrm{eq}}$/cm$^2$. At this fluence, an operation voltage of only 100 V
is needed to achieve 97% hit efficiency, with a power dissipation of 13
mW/cm$^2$ at -25$^{\circ}$C, considerably lower than for previous 3D sensor
generations and planar sensors.Comment: 5 pages, 2 figures, Proceedings of TIPP 2017, Beijing (International
Conference on The Technology and Instrumentation in Particle Physics 2017

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