132 research outputs found
Anomalies, U(1)' and the MSSM
This Thesis reviews an extension of the MSSM by the addition of an anomalous
abelian vector multiplet and contains some original results concerning the
phenomenology of an anomalous . The review part covers an introduction of
the MSSM focusing on its main features, a discussion on the chiral anomalies
and how to cancel them in the Standard Model and by the Green-Schwarz
mechanism. Then, the original results are presented. We build the Lagrangian
for the Minimal Anomalous Extension of the MSSM where the anomalies are
cancelled by the Green-Schwarz mechanism and the addition of Chern-Simons
terms, stressing the main differences between our model and the MSSM. The
advantage of this choice over the standard one is that it allows for arbitrary
values of the quantum numbers of the extra U(1). As a first step towards the
study of hadron annihilations producing four leptons in the final state (a
clean signal which might be studied at LHC) we then compute the decays Z'\to
Z_0 \g and . We find that the largest values of the decay rate
are GeV, while the expected number of events per year at LHC is
at most of the order of 10. Then we compute the relic density predicted by our
model with a new dark matter candidate, the axino, which is the LSP of the
theory. We find agreement with experimental data admitting a bino-higgsino NLSP
or a wino-like NLSP, almost degenerate in mass to the axino.Comment: 145 pages, 29 figures, feynmf, [dvipdfm]{hyperref}, PhD Thesis
(Advisor: F. Fucito), University of Rome Tor Vergat
Super-Heavy Dark Matter - Towards Predictive Scenarios from Inflation
A generic prediction of the Coleman-Weinberg inflation is the existence of a
heavy particle sector whose interactions with the inflaton, the lightest state
in this sector, generate the inflaton potential at loop level. For typical
interactions the heavy sector may contain stable states whose relic abundance
is generated at the end of inflation by the gravity alone. This general
feature, and the absence of any particle physics signal of dark matter so far,
motivates us to look for new directions in the dark sector physics, including
scenarios in which dark matter is super-heavy. In this article we study the
possibility that the dark matter is even heavier than the inflaton, its
existence follows from the inflaton dynamics, and its abundance today is {\it
naturally} determined by the weakness of gravitational interaction. This
implies that the super-heavy dark matter scenarios can be tested via the
measurements of inflationary parameters and/or the CMB isocurvature
perturbations and non-Gaussianities. We explicitly work out details of three
Coleman-Weinberg inflation scenarios, study the systematics of super-heavy dark
matter production in those cases, and compute which parts of the parameter
spaces can be probed by the future CMB measurements.Comment: 10 pages, 4 figures. Matches the published version on NP
Linear inflation from quartic potential
We show that if the inflaton has a non-minimal coupling to gravity and the
Planck scale is dynamically generated, the results of Coleman-Weinberg
inflation are confined in between two attractor solutions: quadratic inflation,
which is ruled out by the recent measurements, and linear inflation which,
instead, is in the experimental allowed region. The minimal scenario has only
one free parameter -- the inflaton's non-minimal coupling to gravity -- that
determines all physical parameters such as the tensor-to-scalar ratio and the
reheating temperature of the Universe. Should the more precise future
measurements of inflationary parameters point towards linear inflation, further
interest in scale-invariant scenarios would be motivated.Comment: 19 pages, 7 figures, revised version published on JHE
Embedding inflation into the Standard Model - more evidence for classical scale invariance
If cosmological inflation is due to a slowly rolling single inflation field
taking trans-Planckian values as suggested by the BICEP2 measurement of
primordial tensor modes in CMB, embedding inflation into the Standard Model
challenges standard paradigm of effective field theories. Together with an
apparent absence of Planck scale contributions to the Higgs mass and to the
cosmological constant, BICEP2 provides further experimental evidence for the
absence of large induced operators. We show that classical scale
invariance, the paradigm that all fundamental scales in Nature are induced by
quantum effects, solves the problem and allows for a remarkably simple
scale-free Standard Model extension with inflaton without extending the gauge
group. Due to trans-Planckian inflaton values and vevs, a dynamically induced
Coleman-Weinberg-type inflaton potential of the model can predict
tensor-to-scalar ratio in a large range, converging around the prediction
of chaotic inflation for a large trans-Planckian value of the
inflaton vev. Precise determination of in future experiments will single
out a unique scale-free inflation potential, allowing to test the proposed
field-theoretic framework.Comment: 20 pages, 6 figures, revised version published on JHE
Phase transition and gravitational wave phenomenology of scalar conformal extensions of the Standard Model
Thermal corrections in classically conformal models typically induce a strong
first-order electroweak phase transition, thereby resulting in a stochastic
gravitational wave background that could be detectable at gravitational wave
observatories. After reviewing the basics of classically conformal scenarios,
in this paper we investigate the phase transition dynamics in a thermal
environment and the related gravitational wave phenomenology within the
framework of scalar conformal extensions of the Standard Model. We find that
minimal extensions involving only one additional scalar field struggle to
reproduce the correct phase transition dynamics once thermal corrections are
accounted for. Next-to-minimal models, instead, yield the desired electroweak
symmetry breaking and typically result in a very strong gravitational wave
signal.Comment: 9 pages and 7 figures. Minor changes to match the published versio
Implications of the effective axial-vector coupling of gluon on top-quark charge asymmetry at the LHC
We study different top quark charge asymmetries and the variation of total cross section induced by the effective axial-vector coupling of gluon
in the LHC experiments. We show that rapidity cut-dependent asymmetries are
more sensitive to the new physics than the independent ones. We also study the
dependence of the asymmetries and variations of total cross sections
on the invariant mass of system and show that it would be necessary
to measure those quantities as functions of at the LHC. In the context
of considered new physics scenario, 7 TeV LHC has enough sensitivity either to
confirm the Tevatron top asymmetry anomaly or to rule it out. In the latter
case the LHC is able to put stringent constraint on the new physics scale
in this framework.Comment: few small changes in the text, Fig. 2 corrected, same as published
version, 12 pages, 9 figure
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