99 research outputs found
Effective Lagrangian approach to neutrinoless double beta decay and neutrino masses
Neutrinoless double beta () decay can in general produce
electrons of either chirality, in contrast with the minimal Standard Model (SM)
extension with only the addition of the Weinberg operator, which predicts two
left-handed electrons in the final state. We classify the lepton number
violating (LNV) effective operators with two leptons of either chirality but no
quarks, ordered according to the magnitude of their contribution to \znbb
decay. We point out that, for each of the three chirality assignments, and , there is only one LNV operator of the corresponding type
to lowest order, and these have dimensions 5, 7 and 9, respectively. Neutrino
masses are always induced by these extra operators but can be delayed to one or
two loops, depending on the number of RH leptons entering in the operator.
Then, the comparison of the decay rate and neutrino masses
should indicate the effective scenario at work, which confronted with the LHC
searches should also eventually decide on the specific model elected by nature.
We also list the SM additions generating these operators upon integration of
the heavy modes, and discuss simple realistic examples of renormalizable
theories for each case.Comment: Accepted for publication. Few misprints corrected and new references
adde
Predictions from Heavy New Physics Interpretation of the Top Forward-Backward Asymmetry
We derive generic predictions at hadron colliders from the large
forward-backward asymmetry observed at the Tevatron, assuming the latter arises
from heavy new physics beyond the Standard Model. We use an effective field
theory approach to characterize the associated unknown dynamics. By fitting the
Tevatron t \bar t data we derive constraints on the form of the new physics.
Furthermore, we show that heavy new physics explaining the Tevatron data
generically enhances at high invariant masses both the top pair production
cross section and the charge asymmetry at the LHC. This enhancement can be
within the sensitivity of the 8 TeV run, such that the 2012 LHC data should be
able to exclude a large class of models of heavy new physics or provide hints
for its presence. The same new physics implies a contribution to the
forward-backward asymmetry in bottom pair production at low invariant masses of
order a permil at most.Comment: 11 pages, 6 figures. v2: added remarks on EFT validity range, dijet
bounds and UV completions; matches published versio
Physics Opportunities of e+e- Linear Colliders
We describe the anticipated experimental program of an e+e- linear collider
in the energy range 500 GeV -- 1.5 TeV. We begin with a description of current
collider designs and the expected experimental environment. We then discuss
precision studies of the W boson and top quark. Finally, we review the range of
models proposed to explain the physics of electroweak symmetry breaking and
show, for each case, the central role that the linear collider experiments will
play in elucidating this physics. (to appear in Annual Reviews of Nuclear and
Particle Science)Comment: 93 pages, latex + 23 figures; typos corrections + 1 reference adde
Impact of massive neutrinos on the Higgs self-coupling and electroweak vacuum stability
The presence of right-handed neutrinos in the type I seesaw mechanism may
lead to significant corrections to the RG evolution of the Higgs self-coupling.
Compared to the Standard Model case, the Higgs mass window can become narrower,
and the cutoff scale become lower. Naively, these effects decrease with
decreasing right-handed neutrino mass. However, we point out that the unknown
Dirac Yukawa matrix may impact the vacuum stability constraints even in the low
scale seesaw case not far away from the electroweak scale, hence much below the
canonical seesaw scale of 10^15 GeV. This includes situations in which
production of right-handed neutrinos at colliders is possible. We illustrate
this within a particular parametrization of the Dirac Yukawas and with explicit
low scale seesaw models. We also note the effect of massive neutrinos on the
top quark Yukawa coupling, whose high energy value can be increased with
respect to the Standard Model case.Comment: 17 pages, 7 figures, minor revisions, version to appear in JHE
Implications of Flavor Dynamics for Fermion Triplet Leptogenesis
We analyze the importance of flavor effects in models in which leptogenesis
proceeds via the decay of Majorana electroweak triplets. We find that depending
on the relative strengths of gauge and Yukawa reactions the asymmetry can
be sizably enhanced, exceeding in some cases an order of magnitude level. We
also discuss the impact that such effects can have for TeV-scale triplets
showing that as long as the asymmetry is produced by the dynamics of the
lightest such triplet they are negligible, but open the possibility for
scenarios in which the asymmetry is generated above the TeV scale by heavier
states, possibly surviving the TeV triplet related washouts. We investigate
these cases and show how they can be disentangled at the LHC by using Majorana
triplet collider observables and, in the case of minimal type III see-saw
models even through lepton flavor violation observables.Comment: 22 pages, 9 figures, extended discussion on collider phenomenology,
references added. Version matches publication in JHE
Higgs boson decay into 2 photons in the type~II Seesaw Model
We study the two photon decay channel of the Standard Model-like component of
the CP-even Higgs bosons present in the type II Seesaw Model. The corresponding
cross-section is found to be significantly enhanced in parts of the parameter
space, due to the (doubly-)charged Higgs bosons' virtual
contributions, while all the other Higgs decay channels remain Standard
Model(SM)-like. In other parts of the parameter space (and
) interfere destructively, reducing the two photon branching ratio
tremendously below the SM prediction. Such properties allow to account for any
excess such as the one reported by ATLAS/CMS at GeV if confirmed
by future data; if not, for the fact that a SM-like Higgs exclusion in the
diphoton channel around 114-115 GeV as reported by ATLAS, does not contradict a
SM-like Higgs at LEP(!), and at any rate, for the fact that ATLAS/CMS exclusion
limits put stringent lower bounds on the mass, particularly in
the parameter space regions where the direct limits from same-sign leptonic
decays of do not apply.Comment: 26 pages, 7 figure
Feynman Rules for the Rational Part of the Standard Model One-loop Amplitudes in the 't Hooft-Veltman Scheme
We study Feynman rules for the rational part of the Standard Model
amplitudes at one-loop level in the 't Hooft-Veltman scheme.
Comparing our results for quantum chromodynamics and electroweak 1-loop
amplitudes with that obtained based on the Kreimer-Korner-Schilcher (KKS)
scheme, we find the latter result can be recovered when our
scheme becomes identical (by setting in our expressions)
with the KKS scheme. As an independent check, we also calculate Feynman rules
obtained in the KKS scheme, finding our results in complete agreement with
formulae presented in the literature. Our results, which are studied in two
different schemes, may be useful for clarifying the
problem in dimensional regularization. They are helpful to eliminate or find
ambiguities arising from different dimensional regularization schemes.Comment: Version published in JHEP, presentation improved, 41 pages, 10
figure
-Two Higgs Doublet Model and its Collider Phenomenology
Smallness of neutrino masses can be explained by introducing a tiny vacuum
expectation value of an extra-Higgs doublet which couples to right-handed
neutrinos (). This situation is naturally realized in -Two Higgs
Doublet Model (THDM), where a TeV-scale seesaw mechanism can work well. We
investigate observable phenomenology of THDM at LHC and ILC experiments.
Charged Higgs boson () in THDM is almost originated from the
extra-Higgs doublet and its coupling strength to neutrinos are not small. Then
this model induces rich phenomenology at the LHC, for example, when
, observable charged tracks can be induced from long lived
charged Higgs. On the other hand, when , right-handed
neutrinos can be long-lived, and secondary vertices may be tagged at the LHC.
The THDM also predicts observable lepton number violating process at the
ILC.Comment: 17 pages, 27 eps file
Regular Exercise or Changing Diet Does Not Influence Aortic Valve Disease Progression in LDLR Deficient Mice
BACKGROUND: The development and progression of calcific aortic valve disease (CAVD) shares a number of similarities with atherosclerosis. Recently we could demonstrate that regular exercise training (ET) as primary prevention prevents aortic valve disease in LDL-receptor deficient (LDLR(-/-)) mice. We aimed to investigate the impact of exercise training on the progression of CAVD in LDLR(-/-) mice in the setting of secondary prevention METHODS AND RESULTS: Sixty-four LDLR(-/-) mice were fed with high cholesterol diet to induce aortic valve sclerosis. Thereafter the animals were divided into 3 groups: group 1 continuing on high cholesterol diet, group 2 continuing with cholesterol diet plus 1 h ET per day, group 3 continuing with normal mouse chow. After another 16 weeks the animal were sacrificed. Histological analysis of the aortic valve thickness demonstrated no significant difference between the three groups (control 98.3±4.5 µm, ET 88.2±6.6 µm, change in diet 87.5±4.0). Immunohistochemical staining for endothelial cells revealed a disrupted endothelial cell layer to the same extend in all groups. Furthermore no difference between the groups was evident with respect to the expression of inflammatory, fibroblastic and osteoblastic markers. CONCLUSION: Based on the present study we have to conclude that once the development of a CAVD is initiated, exercise training or a change in diet does not have the potential to attenuate the progress of the CAVD
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