3,828 research outputs found
Inflation induced by Gravitino Condensation in Supergravity
We discuss the emergence of an inflationary phase in supergravity with the
super-Higgs effect due to dynamical spontaneous breaking of supersymmetry, in
which the role of the inflaton is played by the gravitino condensate. Realistic
models compatible with the Planck satellite CMB data are found in conformal
supergravity scenarios with dynamical gravitino masses that are small compared
to the Planck mass, as could be induced by a non-trivial vacuum expectation
value of the dilaton superfield of appropriate magnitude.Comment: 13 pages, Revtex, 11 pdf figures, references added on role of
gravitino torsion condensates in parallelising space-time manifolds,
hierarchy of scales involved made explicit, no effects on conclusions.
Version to appear in Physical Review
High-Energy QCD as a Topological Field Theory
We propose an identification of the conformal field theory underlying
Lipatov's spin-chain model of high-energy scattering in perturbative QCD. It is
a twisted N=2 supersymmetric topological field theory, which arises as the
limiting case of the SL(2,R)/U(1) non-linear sigma model that also plays a role
in describing the Quantum Hall effect and black holes in string theory. The
doubly-infinite set of non-trivial integrals of motion of the high-energy
spin-chain model displayed by Faddeev and Korchemsky are identified as the
Cartan subalgebra of a W_{\infty} \otimes W_{\infty} bosonic sub-symmetry
possessed by this topological theory. The renormalization group and an analysis
of instanton perturbations yield some understanding why this particular
topological spin-chain model emerges in the high-energy limit, and provide a
new estimate of the asymptotic behaviour of multi-Reggeized-gluon exchange.Comment: 24 pages LATEX, one eps figure incorporate
Light-by-Light Scattering Constraint on Born-Infeld Theory
The recent measurement by ATLAS of light-by-light scattering in LHC Pb-Pb
collisions is the first direct evidence for this basic process. We find that it
requires the mass scale of a nonlinear Born-Infeld extension of QED to be
~GeV, a much stronger constraint than those derived previously. In
the case of a Born-Infeld extension of the Standard Model in which the
U(1) hypercharge gauge symmetry is realized nonlinearly, the limit on
the corresponding mass scale is ~GeV, which in turn imposes a lower
limit of ~TeV on the magnetic monopole mass in such a U(1) Born-Infeld theory.Comment: 11 pages, 4 figures, version accepted for publication in PR
Wess-Zumino Inflation in Light of Planck
We discuss cosmological inflation in the minimal Wess-Zumino model with a
single massive chiral supermultiplet. With suitable parameters and assuming a
plausible initial condition at the start of the inflationary epoch, the model
can yield scalar perturbations in the Cosmic Microwave Background (CMB) of the
correct strength with a spectral index n_s ~ 0.96 and a tensor-to-scalar
perturbation ratio r < 0.1, consistent with the Planck CMB data. We also
discuss the possibility of topological inflation within the Wess-Zumino model,
and the possibility of combining it with a seesaw model for neutrino masses.
This would violate R-parity, but at such a low rate that the lightest
supersymmetric particle would have a lifetime long enough to constitute the
astrophysical cold dark matter.Comment: 11 pages, 3 figure
The Price of an Electroweak Monopole
In a recent paper, Cho, Kim and Yoon (CKY) have proposed a version of the
SU(2) U(1) Standard Model with finite-energy monopole and dyon
solutions. The CKY model postulates that the effective U(1) gauge coupling very rapidly as the Englert-Brout-Higgs vacuum expectation value , but in a way that is incompatible with LHC measurements of the Higgs boson
decay rate. We construct generalizations of the CKY model
that are compatible with the constraint, and calculate
the corresponding values of the monopole and dyon masses. We find that the
monopole mass could be TeV, so that it could be pair-produced at the
LHC and accessible to the MoEDAL experiment.Comment: 15 pages; Two clarifying footnotes (3 and 4) added. No effect on
conclusion
The Higgs Boson Mass from Precision Electroweak Data
We present a new global fit to precision electroweak data, including new low-
and high-energy data and analyzing the radiative corrections arising from the
minimal symmetry breaking sectors of the Standard Model (SM) and its
supersymmetric extension (MSSM). It is shown that present data favor a Higgs
mass of O(M_Z): M_H = 76+152-50 GeV. We confront our analysis with
(meta)stability and perturbative bounds on the SM Higgs mass, and the
theoretical upper bound on the MSSM Higgs mass. Present data do not
discriminate significantly between the SM and MSSM Higgs mass ranges. We
comment in passing on the sensitivity of the Higgs mass determination to the
values of alpha(M_Z) and alpha_s(M_Z).Comment: 10 pages, latex, 8 figures as uu-encoded postscript fil
Environmental CPT Violation in an Expanding Universe in String Theory
We consider a model of an expanding Universe in string theory that yields
`environmental' CPT violation for fermions, in the sense of different
dispersion relations for fermions and antifermions. These are induced by a
cosmological background with constant torsion provided by the Kalb-Ramond
antisymmetric tensor field (axion) of the string gravitational multiplet. This
effect induces different densities of neutrinos and antineutrinos while in
chemical equilibrium, offering new scenarios for leptogenesis and baryogenesis
even in the absence of CP violation.Comment: 8 pages, some clarifying remarks and references added, correction of
typos in the text below eq. (26), no effects on conclusion
Recent advances at NASA in calculating the electronic spectra of diatomic molecules
Advanced entry vehicles, such as the proposed Aero-assisted Orbital Transfer Vehicle, provide new and challenging problems for spectroscopy. Large portions of the flow field about such vehicles will be characterized by chemical and thermal nonequilibrium. Only by considering the actual overlap of the atomic and rotational lines emitted by the species present can the impact of radiative transport within the flow field be assessed correctly. To help make such an assessment, a new computer program is described that can generate high-resolution, line-by-line spectra for any spin-allowed transitions in diatomic molecules. The program includes the matrix elements for the rotational energy and distortion to the fourth order; the spin-orbit, spin-spin, and spin-rotation interactions to first order; and the lambda splitting by a perturbation calculation. An overview of the Computational Chemistry Branch at Ames Research Center is also presented
Search for Quantum Gravity
A satisfactory theory of quantum gravity may necessitate a drastic
modification of our perception of space-time, by giving it a foamy structure at
distances comparable to the Planck length. It is argued in this essay that the
experimental detection of such structures may be a realistic possibility in the
foreseeable future. After a brief review of different theoretical approaches to
quantum gravity and the relationships between them, we discuss various possible
experimental tests of the quantum nature of space-time. Observations of photons
from distant astrophysical sources such as Gamma-Ray Bursters and laboratory
experiments on neutral kaon decays may be sensitive to quantum-gravitational
effects if they are only minimally suppressed. Experimental limits from the
Whipple Observatory and the CPLEAR Collaboration are already probing close to
the Planck scale, and significant increases in sensitivity are feasible.Comment: 7 pages LATEX, no figures, Awarded First Prize in the Gravity
Research Foundation Essay Competition for 199
Liouville Cosmology
Liouville string theory is a natural framework for discussing the
non-equilibrium evolution of the Universe. It enables non-critical strings to
be treated in mathematically consistent manner, in which target time is
identified with a world-sheet renormalization-group scale parameter, preserving
target-space general coordinate invariance and the existence of an S-matrix. We
review our proposals for a unified treatment of inflation and the current
acceleration of the Universe. We link the current acceleration of the Universe
with the value of the string coupling. In such a scenario, the dilaton plays an
essential background role, driving the acceleration of the Universe during the
present era after decoupling as a constant during inflation.Comment: 23 pages latex, 2 eps figures, contribution to the proceedings of the
Dark 2004 conference, College Station, October 200
- …