22 research outputs found
The Axial Anomaly in D=3+1 Light-Cone QED
We consider -dimensional, Dirac electrons of arbitrary mass,
propagating in the presence of electric and magnetic fields which are both
parallel to the axis. The magnetic field is constant in space and time
whereas the electric field depends arbitrarily upon the light-cone time
parameter . We present an explicit solution to the
Heisenberg equations for the electron field operator in this background. The
electric field results in the creation of electron-positron pairs. We compute
the expectation values of the vector and axial vector currents in the presence
of a state which is free vacuum at . Both current conservation and the
standard result for the axial vector anomaly are verified for the first time
ever in -dimensional light-cone QED. An interesting feature of our
operator solution is the fact that it depends in an essential way upon
operators from the characteristic at , in addition to the usual
dependence upon operators at . This dependence survives even in the
limit of infinite . Ignoring the operators leads to a progressive loss
of unitarity, to the violation of current conservation, to the loss of
renormalizability, and to an incorrect result for the axial vector anomaly.Comment: 31 pages, LaTeX 2 epsilon, no figures, some typoes corrected for
publicatio
A D-brane alternative to unification
We propose a minimal embedding of the Standard Model spectrum in a D-brane
configuration of type I string theory. The SU(3) color and SU(2) weak
interactions arise from two different collections of branes. The model is
neither grand unified nor supersymmetric but it naturally leads to the right
prediction of the weak angle for a string scale of the order of a few TeV. It
requires two Higgs doublets and guarantees proton stability.Comment: LateX, 14 pages, one figure; v2: References added, extra comment
added on accomodating right-handed neutrino
Ribbons Around Mexican Hats
We analyze quasi-topological solitons winding around a mexican-hat potential
in two space-time dimensions.
They are prototypes for a large number of physical excitations, including
Skyrmions of the Higgs sector of the standard electroweak model, magnetic
bubbles in thin ferromagnetic films, and strings in certain non-trivial
backgrounds.
We present explicit solutions, derive the conditions for classical stability,
and show that contrary to the naive expectation these can be satisfied in the
weak-coupling limit. In this limit we can calculate the soliton properties
reliably, and estimate their lifetime semiclassically. We explain why gauge
interactions destabilize these solitons, unless the scalar sector is extended.Comment: 12p. Latex , Ecole Polytechnique preprint A295.02.94 and Crete
preprint 94-1
Searching for Extra Dimensions in High Energy Cosmic Rays
We present a study of the decay of an intermediate mini black hole at the
first impact of a cosmic ray particle with the atmosphere, in the context of
D-brane world scenarios with TeV scale gravity and large extra dimensions. We
model the decay of the black hole using the semiclassical approximation and
include the corrections coming from energy loss into the bulk. Extensive
simulations show that mini black hole events are characterized by essentially
different multiplicities and wider lateral distributions of the air showers as
a function of the energy of the incoming primary, as compared to standard
events. Implications for their detection and some open issues on their possible
discovery are also briefly addressed.Comment: 4 pages, 4 figures, Presented by C. Coriano' at the XIII Intl. Symp.
on High Energy Cosmic Rays Interactions, Pylos, Greece, 6-12 Sept. 200
On Spherically-Symmetric Solutions in the Two-Higgs Standard Model
We report the results of a numerical search for non-topological solitons in
the two-Higgs standard model, characterized by the non-trivial winding,
, of the relative phase of the two doublets. In a region of
(weak-coupling) parameter space we identify a branch of winding solutions,
which are lower in energy than the embedded standard sphaleron and deformed
(bi)sphalerons. Contrary, however, to what happens in 2d toy models, these
solutions remain unstable even for very large Higgs masses.Comment: 11 LaTeX pages including 3 .eps figure
One-loop effective action around de Sitter space
The non-local one-loop contribution to the gravitational effective action
around de Sitter space is computed using the background field method with pure
trace external gravitational fields and it is shown to vanish. The calculation
is performed in a generic covariant gauge and the result is verified to be
gauge invariant.Comment: 19 pages, uses phyzzx.tex inpu
Some properties of the Alday-Maldacena minimum
The Alday-Maldacena solution, relevant to the n=4 gluon amplitude in N=4 SYM
at strong coupling, was recently identified as a minimum of the regularized
action in the moduli space of solutions of the AdS_5 sigma-model equations of
motion. Analogous solutions of the Nambu-Goto equations for the n=4 case are
presented and shown to form (modulo the reparametrization group) an equally
large but different moduli space, with the Alday-Maldacena solution at the
intersection of the sigma-model and Nambu-Goto moduli spaces. We comment upon
the possible form of the regularized action for n=5. A function of moduli
parameters z_a is written, whose minimum reproduces the BDDK one-loop
five-gluon amplitude. This function may thus be considered as some kind of
Legendre transform of the BDDK formula and has its own value independently of
the Alday-Maldacena approach.Comment: 10 page
Non trivial generalizations of the Schwinger pair production result
We present new, non trivial generalizations of the recent Tomaras, Tsamis and
Woodard extension of the original Schwinger formula for charged pair production
in a constant field.Comment: 11 page
Non-local SFT Tachyon and Cosmology
Cosmological scenarios built upon the generalized non-local String Field
Theory and -adic tachyons are examined. A general kinetic operator involving
an infinite number of derivatives is studied as well as arbitrary parameter
. The late time dynamics of just the tachyon around the non-perturbative
vacuum is shown to leave the cosmology trivial. A late time behavior of the
tachyon and the scale factor of the FRW metric in the presence of the
cosmological constant or a perfect fluid with is constructed explicitly
and a possibility of non-vanishing oscillations of the total effective state
parameter around the phantom divide is proven.Comment: 17 pages, LaTeX; v2: JHEP3 class is used, references adde
D-branes and the Standard Model
We perform a systematic study of the Standard Model embedding in a D-brane
configuration of type I string theory at the TeV scale. We end up with an
attractive model and we study several phenomenological questions, such as gauge
coupling unification, proton stability, fermion masses and neutrino
oscillations. At the string scale, the gauge group is U(3)_color x U(2)_weak x
U(1)_1 x U(1)_bulk. The corresponding gauge bosons are localized on three
collections of branes; two of them describe the strong and weak interactions,
while the last abelian factor lives on a brane which is extended in two large
extra dimensions with a size of afew microns. The hypercharge is a linear
combination of the first three U(1)s. All remaining U(1)s get masses at the TeV
scale due to anomalies, leaving the baryon and lepton numbers as
(perturbatively) unbroken global symmetries at low energies. The conservation
of baryon number assures proton stability, while lepton number symmetry
guarantees light neutrino masses that involve a right-handed neutrino in the
bulk. The model predicts the value of the weak angle which is compatible with
the experiment when the string scale is in the TeV region. It also contains two
Higgs doublets that provide tree-level masses to all fermions of the heaviest
generation, with calculable Yukawa couplings; one obtains a naturally heavy top
and the correct ratio m_b/m_tau. We also study neutrino masses and mixings in
relation to recent solar and atmospheric neutrino data.Comment: 42 pages, Latex2e, 6 figures, final version to be published in Nucl.
Phys.