78 research outputs found
QCD Running in Lepton Number Violating Meson and Tau Decays
Below the electroweak scale, new physics that violates lepton number in two
units () and is mediated by heavy particle exchange can be
parameterized by a dimension-9 low-energy effective Lagrangian. Operators in
this Lagrangian involving first-generation quarks and leptons contribute to the
short-range mechanism of neutrinoless double beta decay () and
therefore they are strongly constrained. On the other hand, operators with
other quark and lepton families are bounded by the non-observation of different
lepton number violating (LNV) meson and tau decays, such as and . In this work, we
calculate RGE-improved bounds on the Wilson coefficients involved in these
decays. We calculate QCD corrections to the dimension-9 operator basis and find
RG evolution matrices that describe the evolution of the Wilson coefficients
across different energy scales. Unlike the running of operators involved in
-decay, the general flavor structure leads to the mixing of not
only different Lorentz structures but also of different quark-flavor
configurations. Additionally, operators that vanish for the identical lepton
case need to be added to the operator basis. We find new constraints on
previously unbounded operators and the enhancement of bounds for specific
Wilson coefficients. We also find new bounds coming from the mixing between
operators with different quark-flavor configurations.Comment: 26 pages, 2 figures, 14 table
RGE effects on the LFV scale from meson decays
We consider the lepton-flavor violating (LFV) lepton-quark dimension-6
operators and analyze their contributions to the LFV leptonic decays of vector,
pseudoscalar, and scalar neutral mesons as well as to
decays. These operators
contribute to the purely leptonic processes via quark loop. On the basis of
quark-hadron duality, we relate these loops to the appropriate meson-exchange
contributions. In this way, we extract lower bounds on the individual scales of
the studied LFV operators from the experimental and phenomenological limits on
the leptonic decays of mesons and leptons. As a byproduct, we shall obtain new
limits on the LFV leptonic decays of flavored mesons from the experimental
bounds on the three-body lepton decays. We study the effects of QED and QCD
radiative corrections to the LFV lepton-quark operators in question. We derive
for them the one-loop matrix of the RGE evolution and examine its effect on the
previously derived tree-level limits on these operators. We show that the QED
corrections are particularly relevant due to operator mixing. Specifically, for
some of them the limits on their individual LFV scales improve by up to 3
orders of magnitude.Comment: 20 pages, 1 figur
Searching for light neutralinos with a displaced vertex at the LHC
We study a bino-like light neutralino () produced at the LHC
from the decay of a scalar lepton () through the process in the context of R-parity-violating (RPV)
supersymmetry where is the lightest supersymmetric particle.
For small masses and RPV couplings, the neutralino is naturally long-lived and
its decay products can be identified as displaced tracks. Following existing
searches, we propose a displaced-vertex search strategy for such a light
neutralino with a single RPV coupling switched on, , in the
mass range 10\,\mbox{GeV} \lesssim m_{\tilde \chi_1^0}\lesssim
230\,\mbox{GeV}. We perform Monte Carlo simulations and conclude that at the
high-luminosity LHC, the proposed search can probe values of
down to two orders of magnitude smaller than current bounds and up to 40 times
stronger than projected limits from monolepton searches.Comment: 16 pages, 6 figures; v2: comment added, matches version to be
published in JHE
Quark masses and mixings in the RS1 model with a condensing 4th generation
We study the hierarchy of quark masses and mixings in a model based on a
5-dimensional spacetime with constant curvature of Randall-Sundrum type with
two branes, where the Electroweak Symmetry Breaking is caused dynamically by
the condensation of a 4th generation of quarks, due to underlying physics from
the 5D bulk and the first KK gluons. We first study the hierarchy of quark
masses and mixings that can be obtained from purely adjusting the profile
localizations, finding that realistic masses are not reproduced unless non
trivial hierarchies of underlying 4-fermion interactions from the bulk are
included. Then we study global U(1) symmetries that can be imposed in order to
obtain non-symmetric modified Fritzsch-like textures in the mass matrices that
reproduce reasonably well quark masses and CKM mixings.Comment: Minor changes. Version accepted for publication in JHE
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Rarity of monodominance in hyperdiverse Amazonian forests.
Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such "monodominant" forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees ≥ 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors
Estimating the global conservation status of more than 15,000 Amazonian tree species
Estimates of extinction risk for Amazonian plant and animal species are rare and not often incorporated into land-use policy and conservation planning. We overlay spatial distribution models with historical and projected deforestation to show that at least 36% and up to 57% of all Amazonian tree species are likely to qualify as globally threatened under International Union for Conservation of Nature (IUCN) Red List criteria. If confirmed, these results would increase the number of threatened plant species on Earth by 22%. We show that the trends observed in Amazonia apply to trees throughout the tropics, and we predict thatmost of the world’s >40,000 tropical tree species now qualify as globally threatened. A gap analysis suggests that existing Amazonian protected areas and indigenous territories will protect viable populations of most threatened species if these areas suffer no further degradation, highlighting the key roles that protected areas, indigenous peoples, and improved governance can play in preventing large-scale extinctions in the tropics in this century
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