1,746 research outputs found
Dilepton Signal of a Type-II Seesaw at CERN LHC: Reveals a TeV Scale B-L Symmetry
We explore the discovery potential of doubly charged Higgs bosons
(\xi^{\pm\pm}) at the CERN Large Hadron Collider (LHC). For moderate values of
the coupling constants in the original Type-II seesaw model, these
doubly-charged Higgs bosons are not accessible by any present or near future
collider experiments. In a gauged B-L symmetric model we introduce two triplet
scalars to execute a variant of type-II seesaw at the TeV scale. This leads to
a clear like-sign dilepton signal in the decay mode of \xi^{\pm\pm} for a small
vacuum expectation value (\lsim 10^5 \eV) of the triplet scalar \xi= (\xi^{++},
\xi^+, \xi^0) of mass \lsim 1 \TeV. To be specific, for a mass range of
200-1000 GeV of \xi^{\pm\pm}, the like-sign dilepton signal can be detected at
CERN LHC at a center of mass energy 14 TeV with an integrated luminosity > 30
{\rm fb}^{-1}. The same analysis is also pursued with center of mass energies 7
TeV and 10 TeV as well. We also comment on the decay mode of singly charged
scalars and neutral B-L gauge boson in this model.Comment: Minor change in Introduction, Z' contribution to the production of
doubly charged scalars are explicitly shown, new figures added, new
references added. To appear in Physical Review
The U(1) symmetry of the non-tribimaximal pattern in the degenerate mass spectrum case of the neutrino mass matrix
On account of the new neutrino oscillation data signalling a non-zero value
for the smallest mixing angle (), we present an explicit realization
of the underlying U(1) symmetry characterizing the maximal atmospheric mixing
angle () pattern with two degenerate masses but now with
generic values of . We study the effects of the form invariance with
respect to U(1), and/or , subgroups, on the Yukawa couplings and the
mass terms. Later on, we specify to its experimental best fit value
(), and impose the symmetry in an entire model which includes
charged leptons, and many Higgs doublets or standard model singlet heavy
scalars, to show that it can make room for the charged lepton mass hierarchies.
In addition, we show for the non-tribimaximal value of within
type-I seesaw mechanism enhanced with flavor symmetry that neutrino mass
hierarchies can be generated. Furthermore, lepton/baryogenesis can be
interpreted via type-II seesaw mechanism within a setup meeting the flavor
U(1)-symmetry.Comment: latex, 1 table, 20 pages. Typos are corrected, shortened version to
appear in Phys. Rev.
Small neutrino masses due to R-symmetry breaking for a small cosmological constant
We describe a class of supersymmetric models in which neutrinos are kept
light by an R-symmetry. In supergravity, R-symmetry must be broken to allow for
a small cosmological constant after supersymmetry breaking. In the class of
models described here, this R-symmetry breaking results in the generation of
Dirac neutrino masses, connecting the tuning of the cosmological constant to
the puzzle of neutrino masses. Surprisingly, under the assumption of low-scale
supersymmetry breaking and superpartner masses close to a TeV, these masses are
independent of the fundamental supersymmetry-breaking scale, and accommodate
the correct magnitude. This offers a novel explanation for the vastly different
scales of neutrino and charged fermion masses. These models require that
R-symmetric supersymmetry exists at the TeV scale, and predict that neutrino
masses are purely Dirac, implying the absence of neutrino-less double
beta-decay. Interesting collider signals can arise due to charged scalars which
decay leptonically, with branching ratios determined by the neutrino mixing
matrix.Comment: 6 pages, 2 figures. v2 matches published versio
Nonlinear Dynamics in Distributed Systems
We build on a previous statistical model for distributed systems and
formulate it in a way that the deterministic and stochastic processes within
the system are clearly separable. We show how internal fluctuations can be
analysed in a systematic way using Van Kanpen's expansion method for Markov
processes. We present some results for both stationary and time-dependent
states. Our approach allows the effect of fluctuations to be explored,
particularly in finite systems where such processes assume increasing
importance.Comment: Two parts: 8 pages LaTeX file and 5 (uuencoded) figures in Postscript
forma
Classical predictability and coarse-grained evolution of the quantum baker's map
We investigate how classical predictability of the coarse-grained evolution
of the quantum baker's map depends on the character of the coarse-graining. Our
analysis extends earlier work by Brun and Hartle [Phys. Rev. D 60, 123503
(1999)] to the case of a chaotic map. To quantify predictability, we compare
the rate of entropy increase for a family of coarse-grainings in the decoherent
histories formalism. We find that the rate of entropy increase is dominated by
the number of scales characterising the coarse-graining.Comment: 28 pages, 1 figur
A little inflation at the cosmological QCD phase transition
We reexamine the recently proposed "little inflation" scenario that allows
for a strong first order phase-transition of QCD at non-negligible baryon
number in the early universe and its possible observable consequences. The
scenario is based on the assumptions of a strong mechanism for baryogenesis and
a quasistable QCD-medium state which triggers a short inflationary period of
inflation diluting the baryon asymmetry to the value observed today. The
cosmological implications are reexamined, namely effects on primordial density
fluctuations up to dark matter mass scales of M_{max} \sim 1 M_{\astrosun},
change in the spectral slope up to M_{max} \sim 10^6 M_{\astrosun},
production of seeds for the present galactic and extragalactic magnetic fields
and a gravitational wave spectrum with a peak frequency around . We discuss the issue of nucleation in more detail and
employ a chiral effective model of QCD to study the impact on small scale
structure formation.Comment: 18 pages, 12 figures, several extensions to the text and structure
formation part was rephrased for better readabilit
New physics from ultrahigh energy cosmic rays
Cosmic rays from outer space enter the atmosphere with energies of up to
10^{11} GeV. The initial particle or a secondary hadron inside the shower may
then interact with an air nucleon to produce nonstandard particles. In this
article we study the production of new physics by high energy cosmic rays,
focusing on the long-lived gluino of split-SUSY models and a WIMP working as
dark matter. We first deduce the total flux of hadron events at any depth in
the atmosphere, showing that secondary hadrons can not be neglected. Then we
use these results to find the flux of gluinos and WIMPs that reach the ground
after being produced inside air showers. We also evaluate the probability of
producing these exotic particles in a single proton shower of ultrahigh energy.
Finally we discuss the possible signal in current and projected experiments.
While the tiny flux of WIMPs does not seem to have any phenomenological
consequences, we show that the gluinos could modify substantially the profile
of a small fraction of extensive air showers. In particular, they could produce
a distinct signal observable at AUGER in showers of large zenith angle.Comment: 9 pages, version to appear in PR
Unification via intermediate symmetry breaking scales with the quartification gauge group
The idea of quark-lepton universality at high energies has been introduced as
a natural extension to the standard model. This is achieved by endowing leptons
with new degrees of freedom -- leptonic colour, an analogue of the familiar
quark colour. Grand and partially unified models which utilise this new gauge
symmetry SU(3)_\ell have been proposed in the context of the quartification
gauge group SU(3)^4. Phenomenologically successful gauge coupling constant
unification without supersymmetry has been demonstrated for cases where the
symmetry breaking leaves a residual SU(2)_\ell unbroken. Though attractive,
these schemes either incorporate ad hoc discrete symmetries and
non-renormalisable mass terms, or achieve only partial unification. We show
that grand unified models can be constructed where the quartification group can
be broken fully [i.e. no residual SU(2)_\ell] to the standard model gauge group
without requiring additional discrete symmetries or higher dimension operators.
These models also automatically have suppressed nonzero neutrino masses. We
perform a systematic analysis of the renormalisation-group equations for all
possible symmetry breaking routes from SU(3)^4 --> SU(3)_q x SU(2)_L x U(1)_Y.
This analysis indicates that gauge coupling unification can be achieved for
several different symmetry breaking patterns and we outline the requirements
that each gives on the unification scale. We also show that the unification
scenarios of those models which leave a residual SU(2)_\ell symmetry are not
unique. In both symmetry breaking cases, some of the scenarios require new
physics at the TeV scale, while others do not allow for new TeV phenomenology
in the fermionic sector.Comment: 25 page
A Survey of Lepton Number Violation Via Effective Operators
We survey 129 lepton number violating effective operators, consistent with
the minimal Standard Model gauge group and particle content, of mass dimension
up to and including eleven. Upon requiring that each one radiatively generates
the observed neutrino masses, we extract an associated characteristic cutoff
energy scale which we use to calculate other observable manifestations of these
operators for a number of current and future experimental probes, concentrating
on lepton number violating phenomena. These include searches for neutrinoless
double-beta decay and rare meson, lepton, and gauge boson decays. We also
consider searches at hadron/lepton collider facilities in anticipation of the
LHC and the future ILC. We find that some operators are already disfavored by
current data, while more are ripe to be probed by next-generation experiments.
We also find that our current understanding of lepton mixing disfavors a subset
of higher dimensional operators. While neutrinoless double-beta decay is the
most promising signature of lepton number violation for the majority of
operators, a handful is best probed by other means. We argue that a combination
of constraints from various independent experimental sources will help to
pinpoint the ``correct'' model of neutrino mass, or at least aid in narrowing
down the set of possibilities.Comment: 34 pages, 10 eps figures, 1 tabl
Phenomenology of 10^32 Dark Sectors
We postulate an exact permutation symmetry acting on 10^32 Standard Model
copies as the largest possible symmetry extension of the Standard Model. This
setup automatically lowers the fundamental gravity cutoff down to TeV, and
thus, accounts for the quantum stability of the weak scale. We study the
phenomenology of this framework and show that below TeV energies the copies are
well hidden, obeying all the existing observational bounds. Nevertheless, we
identify a potential low energy window into the hidden world, the oscillation
of the neutron into its dark copies. At the same time, proton decay can be
suppressed by gauging the diagonal baryon number of the different copies. This
framework offers an alternative approach to several particle physics questions.
For example, we suggest a novel mechanism for generating naturally small
neutrino masses that are suppressed by the number of neutrino species. The
mirror copies of the Standard Model naturally house dark matter candidates. The
general experimentally observable prediction of this scenario is an emergence
of strong gravitational effects at the LHC. The low energy permutation symmetry
powerfully constrains the form of this new gravitational physics and allows to
make observational predictions, such as, production of micro black-holes with
very peculiar properties.Comment: 36 pages. v2, note added on oscillation of neutral state, Refs. adde
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