599 research outputs found
Experimental tests for the Babu-Zee two-loop model of Majorana neutrino masses
The smallness of the observed neutrino masses might have a radiative origin.
Here we revisit a specific two-loop model of neutrino mass, independently
proposed by Babu and Zee. We point out that current constraints from neutrino
data can be used to derive strict lower limits on the branching ratio of
flavour changing charged lepton decays, such as .
Non-observation of Br() at the level of would rule
out singly charged scalar masses smaller than 590 GeV (5.04 TeV) in case of
normal (inverse) neutrino mass hierarchy. Conversely, decay branching ratios of
the non-standard scalars of the model can be fixed by the measured neutrino
angles (and mass scale). Thus, if the scalars of the model are light enough to
be produced at the LHC or ILC, measuring their decay properties would serve as
a direct test of the model as the origin of neutrino masses.Comment: 14 pages, 16 figure
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The uncertain brain: a co-ordinate based meta-analysis of the neural signatures supporting uncertainty during different contexts
Uncertainty is often inevitable in everyday life and can be both stressful and exciting.
Given its relevance to psychopathology and wellbeing, recent research has begun to
address the brain basis of uncertainty. In the current review we examined whether
there are discrete and shared neural signatures for different uncertain contexts.
From the literature we identified three broad categories of uncertainty currently
empirically studied using functional MRI (fMRI): basic threat and reward uncertainty,
decision-making under uncertainty, and associative learning under uncertainty. We
examined the neural basis of each category by using a coordinate based metaanalysis, where brain activation foci from previously published fMRI experiments
were drawn together (1998-2017; 87 studies). The analyses revealed shared and
discrete patterns of neural activation for uncertainty, such as the insula and
amygdala, depending on the category. Such findings will have relevance for
researchers attempting to conceptualise uncertainty, as well as clinical researchers
examining the neural basis of uncertainty in relation to psychopathology
Isospin breaking in the nucleon mass and the sensitivity of β decays to new physics
We discuss the consequences of the approximate conservation of the vector and axial currents for the hadronic matrix elements appearing in β decay if nonstandard interactions are present. In particular, the isovector (pseudo)scalar charge gS(P) of the nucleon can be related to the difference (sum) of the nucleon masses in the absence of electromagnetic effects. Using recent determinations of these quantities from phenomenological and lattice QCD studies we obtain the accurate values gS=1.02(11) and gP=349(9) in the modified minimal subtraction scheme at μ=2  GeV. The consequences for searches of nonstandard scalar interactions in nuclear β decays are studied, finding for the corresponding Wilson coefficient εS=0.0012(24) at 90% C.L., which is significantly more stringent than current LHC bounds and previous low-energy bounds using less precise gS values. We argue that our results could be rapidly improved with updated computations and the direct calculation of certain ratios in lattice QCD. Finally, we discuss the pion-pole enhancement of gP, which makes β decays much more sensitive to nonstandard pseudoscalar interactions than previously thought
Maximum complexity distribution of a monodimensional ideal gas out of equilibrium
The maximum complexity momentum distribution for an isolated monodimensional
ideal gas out of equilibrium is derived analytically. In a first approximation,
it consists of a double non-overlapping Gaussian distribution. In good
agreement with this result, the numerical simulations of a particular isolated
monodimensional gas, which is abruptly pushed far from equilibrium, shows the
maximum complexity distribution in the decay of the system toward equilibrium.Comment: 12 pages, 4 figure
Radiative Symmetry Breaking of the Minimal Left-Right Symmetric Model
Under the assumption of classical conformal invariance, we study the
Coleman-Weinberg symmetry breaking mechanism in the minimal left-right
symmetric model. This model is attractive as it provides a natural framework
for small neutrino masses and the restoration of parity as a good symmetry of
nature. We find that, in a large fraction of the parameter space, the parity
symmetry is maximally broken by quantum corrections in the Coleman-Weinberg
potential, which are a consequence of the conformal anomaly. As the left-right
symmetry breaking scale is connected to the Planck scale through the
logarithmic running of the dimensionless couplings of the scalar potential, a
large separation of the two scales can be dynamically generated. The symmetry
breaking dynamics of the model was studied using a renormalization group
analysis. Electroweak symmetry breaking is triggered by the breakdown of
left-right symmetry, and the left-right breaking scale is therefore expected in
the few TeV range. The phenomenological implications of the symmetry breaking
mechanism are discussed.Comment: 23 pages, 1 figure; version as published in journal; title changed,
changes in abstract, introduction and conclusion
Lepton Flavor Violation at the Large Hadron Collider
We investigate a potential of discovering lepton flavor violation (LFV) at
the Large Hadron Collider. A sizeable LFV in low energy supersymmetry can be
induced by massive right-handed neutrinos, which can explain neutrino
oscillations via the seesaw mechanism. We investigate a scenario where the
distribution of an invariant mass of two hadronically decaying taus
(\tauh\tauh) from \schizero{2} decays is the same in events with or without
LFV. We first develop a transfer function using this ditau mass distribution to
model the shape of the non-LFV \tauh\mu invariant mass. We then show the
feasibility of extracting the LFV \tauh\mu signal. The proposed technique can
also be applied for a LFV \tauh e search.Comment: 8 pages, 6 figures, accepted for publiucation in PR
New Ways to Soft Leptogenesis
Soft supersymmetry breaking terms involving heavy singlet sneutrinos provide
new sources of lepton number violation and of CP violation. In addition to the
CP violation in mixing, investigated previously, we find that `soft
leptogenesis' can be generated by CP violation in decay and in the interference
of mixing and decay. These additional ways to leptogenesis can be significant
for a singlet neutrino Majorana mass that is not much larger than the
supersymmetry breaking scale, . In contrast to CP violation
in mixing, for some of these new contributions the sneutrino oscillation rate
can be much faster than the decay rate, so that the bilinear scalar term need
not be smaller than its natural scale.Comment: 18 pages, 3 figure
SU(5)-inspired double beta decay
The short-range part of the neutrinoless double beta amplitude is generated via the exchange of exotic particles, such as charged scalars, leptoquarks and/or diquarks. In order to give a sizable contribution to the total decay rate, the masses of these exotics should be of the order of (at most) a few TeV. Here, we argue that these exotics could be the ¿light¿ (i.e., weak-scale) remnants of some B ¿ L violating variants of SU(5). We show that unification of the standard model gauge couplings, consistent with proton decay limits, can be achieved in such a setup without the need to introduce supersymmetry. Since these nonminimal SU(5)-inspired models violate B ¿ L, they generate Majorana neutrino masses and therefore make it possible to explain neutrino oscillation data. The light colored particles of these models can potentially be observed at the LHC, and it might be possible to probe the origin of the neutrino masses with Delta L = 2 violating signals. As particular realizations of this idea, we present two models, one for each of the two possible tree-level topologies of neutrinoless double beta decay
Discrete symmetries and isosinglet quarks in low-energy supersymmetry
Many extensions of the minimal supersymmetric standard model contain
superfields for quarks which are singlets under weak isospin with electric
charge -1/3. We explore the possibility that such isosinglet quarks have low or
intermediate scale masses, but do not mediate rapid proton decay because of a
discrete symmetry. By imposing the discrete gauge anomaly cancellation
conditions, we show that the simplest way to achieve this is to extend the Z_3
"baryon parity" of Ibanez and Ross to the isosinglet quark superfields. This
can be done in three distinct ways. This strategy is not consistent with grand
unification with a simple gauge group, but may find a natural place in
superstring-inspired models, for example. An interesting feature of this
scenario is that proton decay is absolutely forbidden.Comment: 13 pages, MIT-CTP-2345, NUB-3097-94T
Dynamical Electroweak Symmetry Breaking by a Neutrino Condensate
We show that the electroweak symmetry can be broken in a natural and
phenomenologically acceptable way by a neutrino condensate. Therefore, we
assume as particle content only the chiral fermions and gauge bosons of the
Standard Model and in addition right-handed neutrinos. A fundamental Higgs
field is absent. We assume instead that new interactions exist that can
effectively be described as four-fermion interactions and that can become
critical in the neutrino sector. We discuss in detail the coupled
Dirac-Majorana gap equations which lead to a neutrino condensate, electroweak
symmetry breaking and via the dynamical see-saw mechanism to small neutrino
masses. We show that the effective Lagrangian is that of the Standard Model
with massive neutrinos and with a composite Higgs particle. The mass
predictions are consistent with data.Comment: 18 pages, 8 figures; minor clarifications; version to appear in Nucl.
Phys.
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