53 research outputs found
Electroweak Baryogenesis in the Presence of an Isosinglet Quark
We consider the possibility of electroweak baryogenesis in a simple extension
of the standard model with an extra singlet complex scalar and a vector-like
down quark. We show that in the present model the first-order electroweak phase
transition can be strong enough to avoid the baryon asymmetry washout by
sphalerons and that the CP-violating effects can be sufficient to explain the
observed baryon-to-entropy ratio nB/s ~ 10^(-10). Other appealing features of
the model include the generation of a CKM phase from spontaneous CP breaking at
a high energy scale and a possible solution of the strong CP problem through
the natural suppression of the parameter theta.Comment: LaTeX, 19 pages, 2 EPS figures, uses epsf, amsmath, amsfonts, amssym
Complex CKM from Spontaneous CP Violation Without Flavor Changing Neutral Current
We analyse the general constraints on unified gauge models with spontaneous
CP breaking that satisfy the conditions that (i) CP violation in the quark
sector is described by a realistic complex CKM matrix, and (ii) there is no
significant flavor changing neutral current effects in the quark sector. We
show that the crucial requirement in order to conform to the above conditions
is that spontaneous CP breaking occurs at a very high scale by complex vevs of
standard model singlet Higgs fields. Two classes of models are found, one
consisting of pure Higgs extensions and the other one involving fermionic
extensions of the standard model. We give examples of each class and discuss
their possible embeddings into higher unified theories. One of the models has
the interesting property that spontaneous CP violation is triggered by
spontaneous P violation, thereby linking the scale of CP violation to the
seesaw scale for neutrino masses.Comment: Latex file ; 18 pages; No figures; some typos correcte
Spontaneous CP Violation in a SUSY Model with a complex CKM
It is pointed out that the recent measurement of the angle of the
unitarity triangle, providing irrefutable evidence for a complex
Cabibbo-Kobayashi-Maskawa (CKM) matrix, presents a great challenge for
supersymmetric models with spontaneous CP violation. We construct a new minimal
extension of the minimal supersymmetric standard model (MSSM), with spontaneous
CP breaking, which leads to a complex CKM matrix, thus conforming to present
experimental data. This is achieved through the introduction of two singlet
chiral superfields and a vector-like quark chiral superfield which mixes with
the standard quarks. A symmetry is introduced in order to have a
potential solution to the strong CP problem.Comment: 12 pages. Uses the elsart.cls LaTeX class. Minor corrections and
references adde
Mixing in the Presence of Isosinglet Quarks
We analyse transitions in the framework of a minimal extension
of the Standard Model where either a or a isosinglet quark is
added to the standard quark spectrum. In the case of a isosinglet
quark, it is shown that there is a significant region of parameter space where
mixing is sufficiently enhanced to be observed at the next
round of experiments. On the contrary, in the case of a isosinglet
quark, it is pointed out that obtaining a substancial enhancement of mixing, while complying with the experimental constraints on rare
kaon decays, requires a contrived choice of parameters.Comment: 10 pages plus four figures. The figures are not included but are
available upon reques
Aspects of Soft and Spontaneous CP Violation
We study four different models for CP violation: the standard (KM) model, the
aspon model of spontaneous breaking and two models of soft breaking. In all
except the standard model, the strong CP problem is addressed and solved.
Testable predictions for the area of the unitarity triangle and for
(epsilon'/epsilon)_K are emphasized. The issue of CP violation may well become
the first place where the standard model of particle theory is shown
definitively to be deficient. There are two reasons for expecting this to
happen: (1) the strong CP problem is still not understood in the unadorned
standard model and (2) the KM mechanism, although unquestionably present, may
not provide the full explanation of epsilon_K and (epsilon'/epsilon)_K.Comment: 24 pages LaTeX including 4 figures. Minor modification to analysis of
lower bound for d_n, summarized in new Table I
New Physics and Evidence for a Complex CKM
We carefully analyse the present experimental evidence for a complex CKM
matrix, even allowing for New Physics contributions to ,
, , , and the piece of and . We emphasize the crucial r\^
ole played by the angle in both providing irrefutable evidence for a
complex CKM matrix and placing constraints on the size of NP contributions. It
is shown that even if one allows for New Physics a real CKM matrix is excluded
at a 99.92% C.L., and the probability for the phase to be in the
interval is 99.7%.Comment: 24 pages, 15 figures. Revised version, analyses extended to more
general New Physics; C.L. of exclusion of a real CKM matrix include
Minimal Flavour Violation and Multi-Higgs Models
We propose an extension of the hypothesis of Minimal Flavour Violation (MFV)
to general multi-Higgs Models without the assumption of Natural Flavour
Conservation in the Higgs sector. We study in detail under what conditions the
neutral Higgs couplings are only functions of and propose a MFV
expansion for the neutral Higgs couplings to fermions.Comment: 16 pages, no figures. References adde
Theory and phenomenology of two-Higgs-doublet models
We discuss theoretical and phenomenological aspects of two-Higgs-doublet
extensions of the Standard Model. In general, these extensions have scalar
mediated flavour changing neutral currents which are strongly constrained by
experiment. Various strategies are discussed to control these flavour changing
scalar currents and their phenomenological consequences are analysed. In
particular, scenarios with natural flavour conservation are investigated,
including the so-called type I and type II models as well as lepton-specific
and inert models. Type III models are then discussed, where scalar flavour
changing neutral currents are present at tree level, but are suppressed by
either specific ansatze for the Yukawa couplings or by the introduction of
family symmetries. We also consider the phenomenology of charged scalars in
these models. Next we turn to the role of symmetries in the scalar sector. We
discuss the six symmetry-constrained scalar potentials and their extension into
the fermion sector. The vacuum structure of the scalar potential is analysed,
including a study of the vacuum stability conditions on the potential and its
renormalization-group improvement. The stability of the tree level minimum of
the scalar potential in connection with electric charge conservation and its
behaviour under CP is analysed. The question of CP violation is addressed in
detail, including the cases of explicit CP violation and spontaneous CP
violation. We present a detailed study of weak basis invariants which are odd
under CP. A careful study of spontaneous CP violation is presented, including
an analysis of the conditions which have to be satisfied in order for a vacuum
to violate CP. We present minimal models of CP violation where the vacuum phase
is sufficient to generate a complex CKM matrix, which is at present a
requirement for any realistic model of spontaneous CP violation.Comment: v3: 180 pages, 506 references, new chapter 7 with recent LHC results;
referee comments taken into account; submitted to Physics Report
Search for an invisibly decaying Higgs boson or dark matter candidates produced in association with a Z boson in pp collisions at root s=13 TeV with the ATLAS detector
SCOAP
Highly-parallelized simulation of a pixelated LArTPC on a GPU
The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on 10^3 pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype
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