224 research outputs found
Ultimate Intelligence Part I: Physical Completeness and Objectivity of Induction
We propose that Solomonoff induction is complete in the physical sense via
several strong physical arguments. We also argue that Solomonoff induction is
fully applicable to quantum mechanics. We show how to choose an objective
reference machine for universal induction by defining a physical message
complexity and physical message probability, and argue that this choice
dissolves some well-known objections to universal induction. We also introduce
many more variants of physical message complexity based on energy and action,
and discuss the ramifications of our proposals.Comment: Under review at AGI-2015 conference. An early draft was submitted to
ALT-2014. This paper is now being split into two papers, one philosophical,
and one more technical. We intend that all installments of the paper series
will be on the arxi
Dijet resonances, widths and all that
The search for heavy resonances in the dijet channel is part of the on-going
physics programme, both at the Tevatron and at the LHC. Lower limits have been
placed on the masses of dijet resonances predicted in a wide variety of models.
However, across experiments, the search strategy assumes that the effect of the
new particles is well-approximated by on-shell production and subsequent decay
into a pair of jets. We examine the impact of off-shell effects on such
searches, particularly for strongly interacting resonances.Comment: Version published in JHE
Horizontal Symmetry for Quark and Squark Masses in Supersymmetric SU(5)
Recent interest in horizontal symmetry model building has been driven mainly
by the large top mass and hence strong hierarchy in quark masses, and the
possibility of appropriately constrained soft squark mass matrices, in place of
an assumed universality condition, for satisfying the relevant FCNC
constraints. Here we present the first successful SUSY- model that has
such a feature. The horizontal symmetry is a gauged
(). All nonrenormalizable terms compatible with
the symmetry are allowed in the mass matrix constructions. Charged lepton
masses can also be accommodated.Comment: 15 pages, latex, 1 latex figure included version to be published in
Phys. Rev. Lett. ; some small changes in notations and presentation, a small
paragragh and 3 references adde
Decays of metastable vacua in SQCD
The decay rates of metastable SQCD vacua in ISS-type models, both towards
supersymmetric vacua as well as towards other nonsupersymmetric configurations
arising in theories with elementary spectators, are estimated numerically in
the semiclassical approximation by computing the corresponding multifield
bounce configurations. The scaling of the bounce action with respect to the
most relevant dimensionless couplings and ratios of scales is analyzed. In the
case of the decays towards the susy vacua generated by nonperturbative effects,
the results confirm previous analytical estimations of this scaling, obtained
by assuming a triangular potential barrier. The decay rates towards susy vacua
generated by R-symmetry breaking interactions turn out to be more than
sufficiently suppressed for the phenomenologically relevant parameter range,
and their behavior in this regime differs from analytic estimations valid for
parametrically small scale ratios. It is also shown that in models with
spectator fields, even though the decays towards vacua involving nonzero
spectator VEVs don't have a strong parametric dependence on the scale ratios,
the ISS vacuum can still be made long-lived in the presence of R-symmetry
breaking interactions.Comment: 22 pages, 7 figure
Long Lived Fourth Generation and the Higgs
A chiral fourth generation is a simple and well motivated extension of the
standard model, and has important consequences for Higgs phenomenology. Here we
consider a scenario where the fourth generation neutrinos are long lived and
have both a Dirac and Majorana mass term. Such neutrinos can be as light as 40
GeV and can be the dominant decay mode of the Higgs boson for Higgs masses
below the W-boson threshold. We study the effect of the Majorana mass term on
the Higgs branching fractions and reevaluate the Tevatron constraints on the
Higgs mass. We discuss the prospects for the LHC to detect the semi-invisible
Higgs decays into fourth generation neutrino pairs. Under the assumption that
the lightest fourth generation neutrino is stable, it's thermal relic density
can be up to 20% of the observed dark matter density in the universe. This is
in agreement with current constraints on the spin dependent neutrino-neutron
cross section, but can be probed by the next generation of dark matter direct
detection experiments.Comment: v1: 19 pages, 5 figures; v2: References added; v3: version to appear
in JHE
Relations among neutrino observables in the light of a large theta_13 angle
The recent T2K and MINOS indications for a "large" theta_13 neutrino mixing
angle can be accommodated in principle by an infinite number of Yukawa flavour
structures in the seesaw model. Without considering any explicit flavour
symmetry, there is an instructive exercise one can do: to determine the
simplest flavour structures which can account for the data with a minimum
number of parameters, simply assuming these parameters to be uncorrelated. This
approach points towards a limited number of simple structures which show the
minimum complexity a neutrino mass model must generally involve to account for
the data. These basic structures essentially lead to only 4 relations between
the neutrino observables. We emphasize that 2 of these relations, |sin
theta_13|=(tan theta_23/cos delta)*(1-tan theta_12)/(1+tan theta_12) and |sin
theta_13| = sin theta_12 R^1/4, with R= Delta m^2_21/Delta m^2_32, have several
distinctive properties. First, they hold not only with a minimum number of
parameters, but also for complete classes of more general models. Second, any
value of theta_13 within the T2K and MINOS ranges can be obtained from these
relations by taking into account small perturbations. Third, they turn out to
be the pivot relations of models with approximate conservation of lepton
number, which allow the seesaw interactions to induce observable flavour
violating processes, such as mu -> e gamma and tau -> mu gamma. Finally, in
specific cases of this kind, these structures have the rather unique property
to allow a full reconstruction of the seesaw Lagrangian from low energy data.Comment: 13 pages, 3 figure
Heavy colored resonances in top-antitop + jet at the LHC
The LHC is the perfect environment for the study of new physics in the top
quark sector. We study the possibility of detecting signals of heavy
color-octet vector resonances, through the charge asymmetry, in top-antitop+jet
events. Besides contributions with the top-antitop pair in a color-singlet
state, the asymmetry gets also contributions which are proportional to the
color factor f_{abc}^2. This process is particularly interesting for
extra-dimensional models, where the inclusive charge asymmetry generated by
Kaluza-Klein excitations of the gluon vanishes at the tree level. We find that
the statistical significance for the measurement of such an asymmetry is
sizable for different values of the coupling constants and already at low
energies
Three-generation Models from E_8 Magnetized Extra Dimensional Theory
We study 10D super Yang-Mills E8 theory on the 6D torus compactification with
magnetic fluxes. We study systematically the possibilities for realizing 4D
supersymmetric standard models with three generations of quarks and leptons. We
also study quark mass matrices.Comment: 30 page
LHC Predictions from a Tevatron Anomaly in the Top Quark Forward-Backward Asymmetry
We examine the implications of the recent CDF measurement of the top-quark
forward-backward asymmetry, focusing on a scenario with a new color octet
vector boson at 1-3 TeV. We study several models, as well as a general
effective field theory, and determine the parameter space which provides the
best simultaneous fit to the CDF asymmetry, the Tevatron top pair production
cross section, and the exclusion regions from LHC dijet resonance and contact
interaction searches. Flavor constraints on these models are more subtle and
less severe than the literature indicates. We find a large region of allowed
parameter space at high axigluon mass and a smaller region at low mass; we
match the latter to an SU(3)xSU(3)/SU(3) coset model with a heavy vector-like
fermion. Our scenario produces discoverable effects at the LHC with only 1-2
inverse femtobarns of luminosity at 7-8 TeV. Lastly, we point out that a
Tevatron measurement of the b-quark forward-backward asymmetry would be very
helpful in characterizing the physics underlying the top-quark asymmetry.Comment: 35 pages, 10 figures, 4 table
Vanishing Minors in the Neutrino Mass Matrix from Abelian Gauge Symmetries
Augmenting the Standard Model by three right-handed neutrinos allows for an
anomaly-free gauge group extension G_max = U(1)_(B-L) x U(1)_(L_e-L_mu) x
U(1)_(L_mu-L_tau). While simple U(1) subgroups of G_max have already been
discussed in the context of approximate flavor symmetries, we show how two-zero
textures in the right-handed neutrino Majorana mass matrix can be enforced by
the flavor symmetry, which is spontaneously broken very economically by singlet
scalars. These zeros lead to two vanishing minors in the low-energy neutrino
mass matrix after the seesaw mechanism. This study may provide a new testing
ground for a zero-texture approach: the different classes of two-zero textures
with almost identical neutrino oscillation phenomenology can in principle be
distinguished by their different Z' interactions at colliders.Comment: 12 pages; Extended and clarified discussion; comments on finetuning
in the textures; matches published versio
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