17 research outputs found
Decoupling of Degenerate Positive-norm States in Witten's String Field Theory
We show that the degenerate positive-norm physical propagating fields of the
open bosonic string can be gauged to the higher rank fields at the same mass
level. As a result, their scattering amplitudes can be determined from those of
the higher spin fields. This phenomenon arises from the existence of two types
of zero-norm states with the same Young representations as those of the
degenerate positive-norm states in the old covariant first quantized (OCFQ)
spectrum. This is demonstrated by using the lowest order gauge transformation
of Witten's string field theory (WSFT) up to the fourth massive level
(spin-five), and is found to be consistent with conformal field theory
calculation based on the first quantized generalized sigma-model approach. In
particular, on-shell conditions of zero-norm states in OCFQ stringy gauge
transformation are found to correspond, in a one-to-one manner, to the
background ghost fields in off-shell gauge transformation of WSFT. The
implication of decoupling of scalar modes on Sen's conjectures was also briefly
discussed.Comment: 18 pages, use Latex with revtex
Signals for Lorentz Violation in Electrodynamics
An investigation is performed of the Lorentz-violating electrodynamics
extracted from the renormalizable sector of the general Lorentz- and
CPT-violating standard-model extension. Among the unconventional properties of
radiation arising from Lorentz violation is birefringence of the vacuum. Limits
on the dispersion of light produced by galactic and extragalactic objects
provide bounds of 3 x 10^{-16} on certain coefficients for Lorentz violation in
the photon sector. The comparative spectral polarimetry of light from
cosmologically distant sources yields stringent constraints of 2 x 10^{-32}.
All remaining coefficients in the photon sector are measurable in
high-sensitivity tests involving cavity-stabilized oscillators. Experimental
configurations in Earth- and space-based laboratories are considered that
involve optical or microwave cavities and that could be implemented using
existing technology.Comment: 23 pages REVTe
Quantum Theory of Noncommutative Fields
Generalizing the noncommutative harmonic oscillator construction, we propose
a new extension of quantum field theory based on the concept of "noncommutative
fields". Our description permits to break the usual particle-antiparticle
degeneracy at the dispersion relation level and introduces naturally an
ultraviolet and an infrared cutoff. Phenomenological bounds for these new
energy scales are given.Comment: LaTeX file, JHEP3.cls, subequations.sty; 12 pages, no figures. Final
version published in JHEP with some references adde
Ghost Condensation and a Consistent Infrared Modification of Gravity
We propose a theoretically consistent modification of gravity in the
infrared, which is compatible with all current experimental observations. This
is an analog of Higgs mechanism in general relativity, and can be thought of as
arising from ghost condensation--a background where a scalar field \phi has a
constant velocity, = M^2. The ghost condensate is a new kind of
fluid that can fill the universe, which has the same equation of state, \rho =
-p, as a cosmological constant, and can hence drive de Sitter expansion of the
universe. However, unlike a cosmological constant, it is a physical fluid with
a physical scalar excitation, which can be described by a systematic effective
field theory at low energies. The excitation has an unusual low-energy
dispersion relation \omega^2 \sim k^4 / M^2. If coupled to matter directly, it
gives rise to small Lorentz-violating effects and a new long-range 1/r^2 spin
dependent force. In the ghost condensate, the energy that gravitates is not the
same as the particle physics energy, leading to the possibility of both sources
that can gravitate and antigravitate. The Newtonian potential is modified with
an oscillatory behavior starting at the distance scale M_{Pl}/M^2 and the time
scale M_{Pl}^2/M^3. This theory opens up a number of new avenues for attacking
cosmological problems, including inflation, dark matter and dark energy.Comment: 42 pages, LaTeX 2
String Theoretic Bounds on Lorentz-Violating Warped Compactification
We consider warped compactifications that solve the 10 dimensional
supergravity equations of motion at a point, stabilize the position of a
D3-brane world, and admit a warp factor that violates Lorentz invariance along
the brane. This gives a string embedding of ``asymmetrically warped'' models
which we use to calculate stringy (\alpha') corrections to standard model
dispersion relations, paying attention to the maximum speeds for different
particles. We find, from the dispersion relations, limits on gravitational
Lorentz violation in these models, improving on current limits on the speed of
graviton propagation, including those derived from field theoretic loops. We
comment on the viability of models that use asymmetric warping for self-tuning
of the brane cosmological constant.Comment: 20pg, JHEP3; v2 additional references, slight change to intro; v3.
added referenc
Categorizing Different Approaches to the Cosmological Constant Problem
We have found that proposals addressing the old cosmological constant problem
come in various categories. The aim of this paper is to identify as many
different, credible mechanisms as possible and to provide them with a code for
future reference. We find that they all can be classified into five different
schemes of which we indicate the advantages and drawbacks.
Besides, we add a new approach based on a symmetry principle mapping real to
imaginary spacetime.Comment: updated version, accepted for publicatio
Standard Model with Partial Gauge Invariance
We argue that an exact gauge invariance may disable some generic features of
the Standard Model which could otherwise manifest themselves at high energies.
One of them might be related to the spontaneous Lorentz invariance violation
(SLIV) which could provide an alternative dynamical approach to QED and
Yang-Mills theories with photon and non-Abelian gauge fields appearing as
massless Nambu-Goldstone bosons. To see some key features of the new physics
expected we propose partial rather than exact gauge invariance in an extended
SM framework. This principle applied, in some minimal form, to the weak
hypercharge gauge field B_{mu} and its interactions leads to SLIV with B field
components appearing as the massless Nambu-Goldstone modes, and provides a
number of distinctive Lorentz beaking effects. Being naturally suppressed at
low energies they may become detectable in high energy physics and
astrophysics. Some of the most interesting SLIV processes are considered in
significant detail.Comment: 32 pages, extended version, to appear in Eur.Phys.J.
Physics with the KLOE-2 experiment at the upgraded DANE
Investigation at a --factory can shed light on several debated issues
in particle physics. We discuss: i) recent theoretical development and
experimental progress in kaon physics relevant for the Standard Model tests in
the flavor sector, ii) the sensitivity we can reach in probing CPT and Quantum
Mechanics from time evolution of entangled kaon states, iii) the interest for
improving on the present measurements of non-leptonic and radiative decays of
kaons and eta/eta mesons, iv) the contribution to understand the
nature of light scalar mesons, and v) the opportunity to search for narrow
di-lepton resonances suggested by recent models proposing a hidden dark-matter
sector. We also report on the physics in the continuum with the
measurements of (multi)hadronic cross sections and the study of gamma gamma
processes.Comment: 60 pages, 41 figures; added affiliation for one of the authors; added
reference to section