166 research outputs found
The LHC di-photon excess and Gauge Coupling Unification in Extra Heterotic-String Derived Models
The di-photon excess observed at the LHC can be explained as a Standard Model
singlet that is produced and decays by heavy vector-like colour triplets and
electroweak doublets in one-loop diagrams. The characteristics of the required
spectrum are well motivated in heterotic-string constructions that allow for a
light . Anomaly cancellation of the symmetry
requires the existence of the Standard Model singlet and vector-like states in
the vicinity of the breaking scale. In this paper we show
that the agreement with the gauge coupling data at one-loop is identical to the
case of the Minimal Supersymmetric Standard Model, owing to cancellations
between the additional states. We further show that effects arising from heavy
thresholds may push the supersymmetric spectrum beyond the reach of the LHC,
while maintaining the agreement with the gauge coupling data. We show that the
string inspired model can indeed account for the observed signal and discuss
the feasibility of obtaining viable scalar mass spectrum.Comment: 26 pages. 11 figures. Published versio
Novel SM-like Higgs decay into displaced heavy neutrino pairs in U(1)' models
We examine the observability of heavy neutrino (nu_h) signatures of a U(1)'
enlarged Standard Model (SM) encompassing three heavy Majorana neutrinos
alongside the known light neutrino states at the the Large Hadron Collider
(LHC). We show that heavy neutrinos can be rather long-lived particles
producing distinctive displaced vertices that can be accessed in the CERN LHC
detectors. We concentrate here on the gluon fusion production mechanism gg ->
H_{1,2} -> nu_h nu_h, where H_1 is the discovered SM-like Higgs and H_2 is a
heavier state, yielding displaced leptons following nu_h decays into weak gauge
bosons. Using data collected by the end of the LHC Run 2, these signatures
would prove to be accessible with negligibly small background.Comment: 30 pages, journal versio
Comments on Anomaly Cancellations by Pole Subtractions and Ghost Instabilities with Gravity
We investigate some aspects of anomaly cancellation realized by the
subtraction of an anomaly pole, stressing on some of its properties in
superspace. In a local formulation these subtractions can be described in terms
of a physical scalar, an axion and related ghosts. They appear to be necessary
for the unitarization of the theory in the ultraviolet, but they may generate
an infrared instability of the corresponding effective action, signalled by
ghost condensation. In particular the subtraction of the superanomaly multiplet
by a pole in superspace is of dubious significance, due to the different nature
of the chiral and conformal anomalies. In turn, this may set more stringent
constraints on the coupling of supersymmetric theories to gravity.Comment: 18 pages. Revised version. To appear in "Classical and Quantum
Gravity
Wilsonian dark matter in string derived Z' model
The dark matter issue is among the most perplexing in contemporary physics.
The problem is more enigmatic due to the wide range of possible solutions,
ranging from the ultra-light to the super-massive. String theory gives rise to
plausible dark matter candidates due to the breaking of the non--Abelian Grand
Unified Theory (GUT) symmetries by Wilson lines. The physical spectrum then
contains states that do not satisfy the quantisation conditions of the unbroken
GUT symmetry. Given that the Standard Model states are identified with broken
GUT representations, and provided that any ensuing symmetry breaking is induced
by components of GUT states, leaves a remnant discrete symmetry that forbid the
decay of the Wilsonian states. A class of such states are obtained in a
heterotic-string derived model. The model exploits the spinor-vector
duality symmetry, observed in the fermionic heterotic-string
orbifolds, to generate a symmetry that may remain unbroken
down to low energies. The symmetry is broken at the string level with
discrete Wilson lines. The Wilsonian dark matter candidates in the string
derived model are , and hence Standard Model, singlets and possess
non- charges. Depending on the
breaking scale and the reheating temperature they give rise to different
scenarios for the relic abundance, and in accordance with the cosmological
constraints.Comment: 24 pages. 5 figures. Standard LaTex. Additional comments and
clarifications. Published versio
Meccanica quantistica e "lensing" gravitazionale
La deflessione della luce in un campo gravitazionale è una delle prove sperimentali più rilevanti della relatività generale. In questo contesto si discutono alcuni effetti della meccanica quantistica sulla propagazione dei fotoni in uno spazio-tempo curvo. In particolare si presentano le correzioni quantistiche del Modello Standard delle particelle elementari alla diffusione del fotone da una sorgente gravitazionale
Graviton Vertices and the Mapping of Anomalous Correlators to Momentum Space for a General Conformal Field Theory
We investigate the mapping of conformal correlators and of their anomalies
from configuration to momentum space for general dimensions, focusing on the
anomalous correlators , - involving the energy-momentum tensor
with a vector or a scalar operator () - and the 3-graviton vertex
. We compute the , and one-loop vertex functions in
dimensional regularization for free field theories involving conformal scalar,
fermion and vector fields. Since there are only one or two independent tensor
structures solving all the conformal Ward identities for the or
vertex functions respectively, and three independent tensor structures for the
vertex, and the coefficients of these tensors are known for free fields,
it is possible to identify the corresponding tensors in momentum space from the
computation of the correlators for free fields. This works in general
dimensions for and correlators, but only in 4 dimensions for ,
since vector fields are conformal only in . In this way the general
solution of the Ward identities including anomalous ones for these correlators
in (Euclidean) position space, found by Osborn and Petkou is mapped to the
ordinary diagrammatic one in momentum space. We give simplified expressions of
all these correlators in configuration space which are explicitly Fourier
integrable and provide a diagrammatic interpretation of all the contact terms
arising when two or more of the points coincide. We discuss how the anomalies
arise in each approach [...]Comment: 57 pages, 7 figures. Refs adde
Microbiologic characteristics and predictors of mortality in bloodstream infections in intensive care unit patients: A 1-year, large, prospective surveillance study in 5 Italian hospitals
Bloodstream infections (BSIs) from multidrug-resistant (MDR) bacteria cause morbidity and mortality in intensive care unit (ICU) patients worldwide. This study investigated the incidence of BSIs in 5 adult general ICUs in Rome, Italy, and evaluated the mortality rate and risk factors associated with these infections
Two loop electroweak corrections to and in the B-LSSM
The rare decays and are important to research new physics beyond standard model. In
this work, we investigate two loop electroweak corrections to and in the minimal
supersymmetric extension of the SM with local gauge symmetry (B-LSSM),
under a minimal flavor violating assumption for the soft breaking terms. In
this framework, new particles and new definition of squarks can affect the
theoretical predictions of these two processes, with respect to the MSSM.
Considering the constraints from updated experimental data, the numerical
results show that the B-LSSM can fit the experimental data for the branching
ratios of and . The
results of the rare decays also further constrain the parameter space of the
B-LSSM.Comment: 33 pages, 9 figures, Published in EPJ
Shedding light on X17: community report
The workshop “Shedding light on X17” brings together scientists looking for the existence of a possible new light particle, often referred to as X17. This hypothetical particle can explain the resonant structure observed at ∼ 17 MeV in the invariant mass of electron-positron pairs, produced after excitation of nuclei such as 8Be and 4He by means of proton beams at the Atomki Laboratory in Debrecen. The purpose of the workshop is to discuss implications of this anomaly, in particular theoretical interpretations as well as present and future experiments aiming at confirming the result and/or at providing experimental evidence for its interpretation
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