86 research outputs found
CP properties of symmetry-constrained two-Higgs-doublet models
The two-Higgs-doublet model can be constrained by imposing Higgs-family
symmetries and/or generalized CP symmetries. It is known that there are only
six independent classes of such symmetry-constrained models. We study the CP
properties of all cases in the bilinear formalism. An exact symmetry implies CP
conservation. We show that soft breaking of the symmetry can lead to
spontaneous CP violation (CPV) in three of the classes.Comment: 14 pages, 2 tables, revised version adapted to the journal
publicatio
Two experiments for the price of one? -- The role of the second oscillation maximum in long baseline neutrino experiments
We investigate the quantitative impact that data from the second oscillation
maximum has on the performance of wide band beam neutrino oscillation
experiments. We present results for the physics sensitivities to standard three
flavor oscillation, as well as results for the sensitivity to non-standard
interactions. The quantitative study is performed using an experimental setup
similar to the Fermilab to DUSEL Long Baseline Neutrino Experiment (LBNE). We
find that, with the single exception of sensitivity to the mass hierarchy, the
second maximum plays only a marginal role due to the experimental difficulties
to obtain a statistically significant and sufficiently background-free event
sample at low energies. This conclusion is valid for both water Cherenkov and
liquid argon detectors. Moreover, we confirm that non-standard neutrino
interactions are very hard to distinguish experimentally from standard
three-flavor effects and can lead to a considerable loss of sensitivity to
\theta_{13}, the mass hierarchy and CP violation.Comment: RevTex 4.1, 23 pages, 10 figures; v2: Typos corrected, very minor
clarifications; matches published version; v3: Fixed a typo in the first
equation in sec. III
Higgs-mediated FCNCs: Natural Flavour Conservation vs. Minimal Flavour Violation
We compare the effectiveness of two hypotheses, Natural Flavour Conservation
(NFC) and Minimal Flavour Violation (MFV), in suppressing the strength of
flavour-changing neutral-currents (FCNCs) in models with more than one Higgs
doublet. We show that the MFV hypothesis, in its general formulation, is more
stable in suppressing FCNCs than the hypothesis of NFC alone when quantum
corrections are taken into account. The phenomenological implications of the
two scenarios are discussed analysing meson-antimeson mixing observables and
the rare decays B -> mu+ mu-. We demonstrate that, introducing flavour-blind CP
phases, two-Higgs doublet models respecting the MFV hypothesis can accommodate
a large CP-violating phase in Bs mixing, as hinted by CDF and D0 data and,
without extra free parameters, soften significantly in a correlated manner the
observed anomaly in the relation between epsilon_K and S_psi_K.Comment: 27 pages, 4 figures. v3: minor modifications (typos corrected and few
refs. added), conclusions unchanged; journal versio
The C2HDM revisited
The complex two-Higgs doublet model is one of the simplest ways to extend the
scalar sector of the Standard Model to include a new source of CP-violation.
The model has been used as a benchmark model to search for CP-violation at the
LHC and as a possible explanation for the matter-antimatter asymmetry of the
Universe. In this work, we re-analyse in full detail the softly broken
symmetric complex two-Higgs doublet model (C2HDM). We provide
the code C2HDM_HDECAY implementing the C2HDM in the well-known HDECAY program
which calculates the decay widths including the state-of-the-art higher order
QCD corrections and the relevant off-shell decays. Using C2HDM_HDECAY together
with the most relevant theoretical and experimental constraints, including
electric dipole moments (EDMs), we review the parameter space of the model and
discuss its phenomenology. In particular, we find cases where large CP-odd
couplings to fermions are still allowed and provide benchmark points for these
scenarios. We examine the prospects of discovering CP-violation at the LHC and
show how theoretically motivated measures of CP-violation correlate with
observables.The work of D.F., J.C.R. and J.P.S. is supported in part by the Portuguese Fundacao para a Ciencia e Tecnologia (FCT) under contracts CERN/FIS-NUC/0010/2015 and UID/FIS/00777/2013. MM acknowledges financial support from the DFG project "Precision Calculations in the Higgs Sector - Paving the Way to the New Physics Landscape" (ID: MU 3138/1-1).info:eu-repo/semantics/publishedVersio
New Constraints (and Motivations) for Abelian Gauge Bosons in the MeV-TeV Mass Range
We survey the phenomenological constraints on abelian gauge bosons having
masses in the MeV to multi-GeV mass range (using precision electroweak
measurements, neutrino-electron and neutrino-nucleon scattering, electron and
muon anomalous magnetic moments, upsilon decay, beam dump experiments, atomic
parity violation, low-energy neutron scattering and primordial
nucleosynthesis). We compute their implications for the three parameters that
in general describe the low-energy properties of such bosons: their mass and
their two possible types of dimensionless couplings (direct couplings to
ordinary fermions and kinetic mixing with Standard Model hypercharge). We argue
that gauge bosons with very small couplings to ordinary fermions in this mass
range are natural in string compactifications and are likely to be generic in
theories for which the gravity scale is systematically smaller than the Planck
mass - such as in extra-dimensional models - because of the necessity to
suppress proton decay. Furthermore, because its couplings are weak, in the
low-energy theory relevant to experiments at and below TeV scales the charge
gauged by the new boson can appear to be broken, both by classical effects and
by anomalies. In particular, if the new gauge charge appears to be anomalous,
anomaly cancellation does not also require the introduction of new light
fermions in the low-energy theory. Furthermore, the charge can appear to be
conserved in the low-energy theory, despite the corresponding gauge boson
having a mass. Our results reduce to those of other authors in the special
cases where there is no kinetic mixing or there is no direct coupling to
ordinary fermions, such as for recently proposed dark-matter scenarios.Comment: 49 pages + appendix, 21 figures. This is the final version which
appears in JHE
Two-Higgs Leptonic Minimal Flavour Violation
We construct extensions of the Standard Model with two Higgs doublets, where
there are flavour changing neutral currents both in the quark and leptonic
sectors, with their strength fixed by the fermion mixing matrices and
. These models are an extension to the leptonic sector of the class
of models previously considered by Branco, Grimus and Lavoura, for the quark
sector. We consider both the cases of Dirac and Majorana neutrinos and identify
the minimal discrete symmetry required in order to implement the models in a
natural way.Comment: 25 pages. No figure
Flavour-changing top decays in the aligned two-Higgs-doublet model
We perform a complete one-loop computation of the two-body flavour-changing top decays t --> ch and t --> cV (V = gamma, Z), within the aligned two-Higgs-doublet model. We evaluate the impact of the model parameters on the associated branching ratios, taking into account constraints from flavour data and measurements of the Higgs properties. Assuming that the 125 GeV Higgs corresponds to the lightest CP-even scalar of the CP-conserving aligned two-Higgs-doublet model, we find that the rates for such flavour-changing top decays lie below the expected sensitivity of the future high-luminosity phase of the LHC. Measurements of the Higgs signal strength in the di-photon channel are found to play an important role in limiting the size of the t --> ch decay rate when the charged scalar of the model is light
Non-Standard Interactions at a Neutrino Factory: Correlations and CP violation
We explore the potential of several Neutrino Factory (NF) setups to
constrain, discover and measure new physics effects due to Non-Standard
Interactions (NSI) in propagation through Earth matter. We first study the
impact of NSI in the measurement of : we find that these could be
large due to strong correlations of with NSI parameters in the
golden channel, and the inclusion of a detector at the magic baseline is
crucial in order to reduce them as much as possible. We present, then, the
sensitivity of the considered NF setups to the NSI parameters, paying special
attention to correlations arising between them and the standard oscillation
parameters, when all NSI parameters are introduced at once. Off-diagonal NSI
parameters could be tested down to the level of , whereas the diagonal
combinations and
can be tested down to and
, respectively. The possibilities of observing CP violation in this
context are also explored, by presenting a first scan of the CP discovery
potential of the NF setups to the phases and
. We study separately the case where CP violation comes only from
non-standard sources, and the case where it is entangled with the standard
source, . In case turns out to be CP conserving, the
interesting possibility of observing CP violation for reasonably small values
of the NSI parameters emerges.Comment: Final note added. 38 pages, 11 figure
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