5,879 research outputs found
The time travel paradox
We define the time travel paradox in physical terms and prove its existence
by constructing an explicit example. We argue further that in theories -- such
as general relativity -- where the spacetime geometry is subject to nothing but
differential equations and initial data no paradoxes arise.Comment: Minor changes + an explanatory note concerning the lions with the
same world line
Self-force of a point charge in the space-time of a massive wormhole
We consider the self-potential and the self-force for an electrically charged
particle at rest in the massive wormhole space-time. We develop general
approach for the renormalization of electromagnetic field of such particle in
the static space-times and apply it to the space-time of the wormhole with
parameter of the mass, . The self-force is found in manifest form; it is an
attractive force. We discus the peculiarities due to massive parameter of the
wormhole.Comment: 10 pages, 1 figure text correcte
Quantum time machine
The continuation of Misner space into the Euclidean region is seen to imply
the topological restriction that the period of the closed spatial direction
becomes time-dependent. This restriction results in a modified Lorentzian
Misner space in which the renormalized stress-energy tensor for quantized
complex massless scalar fields becomes regular everywhere, even on the
chronology horizon. A quantum-mechanically stable time machine with just the
sub-microscopic size may then be constructed out of the modified Misner space,
for which the semiclassical Hawking's chronology protection conjecture is no
longer an obstruction.Comment: 6 pages, RevTe
Higgs bosons in the simplest SUSY models
Nowadays in the MSSM the moderate values of are almost excluded
by LEP II lower bound on the lightest Higgs boson mass. In the Next-to-Minimal
Supersymmetric Standard Model the theoretical upper bound on it increases and
reaches maximal value in the strong Yukawa coupling limit when all solutions of
renormalization group equations are concentrated near the quasi-fixed point.
For calculation of Higgs boson spectrum the perturbation theory method can be
applied. We investigate the particle spectrum in the framework of the modified
NMSSM which leads to the self-consistent solution in the strong Yukawa coupling
limit. This model allows one to get GeV at values of
. In the investigated model the lightest Higgs boson mass
does not exceed GeV. The upper bound on the lightest CP-even
Higgs boson mass in more complicated supersymmetric models is also discussed.Comment: 27 pages, 5 figures included, LaTeX 2e. Plenary talk at the
Conference of RAS Nuclear Physics Department 2000 in ITEP, Moscow, Russia; to
appear in Phys. Atom. Nuc
Fundamental limitations on "warp drive" spacetimes
"Warp drive" spacetimes are useful as "gedanken-experiments" that force us to
confront the foundations of general relativity, and among other things, to
precisely formulate the notion of "superluminal" communication. We verify the
non-perturbative violation of the classical energy conditions of the Alcubierre
and Natario warp drive spacetimes and apply linearized gravity to the
weak-field warp drive, testing the energy conditions to first and second order
of the non-relativistic warp-bubble velocity. We are primarily interested in a
secondary feature of the warp drive that has not previously been remarked upon,
if it could be built, the warp drive would be an example of a "reaction-less
drive". For both the Alcubierre and Natario warp drives we find that the
occurrence of significant energy condition violations is not just a high-speed
effect, but that the violations persist even at arbitrarily low speeds.
An interesting feature of this construction is that it is now meaningful to
place a finite mass spaceship at the center of the warp bubble, and compare the
warp field energy with the mass-energy of the spaceship. There is no hope of
doing this in Alcubierre's original version of the warp-field, since by
definition the point in the center of the warp bubble moves on a geodesic and
is "massless". That is, in Alcubierre's original formalism and in the Natario
formalism the spaceship is always treated as a test particle, while in the
linearized theory we can treat the spaceship as a finite mass object. For both
the Alcubierre and Natario warp drives we find that even at low speeds the net
(negative) energy stored in the warp fields must be a significant fraction of
the mass of the spaceship.Comment: 18 pages, Revtex4. V2: one reference added, some clarifying comments
and discussion, no physics changes, accepted for publication in Classical and
Quantum Gravit
Particle spectrum in the modified NMSSM in the strong Yukawa coupling limit
A theoretical analysis of solutions of renormalisation group equations in the
MSSM corresponding to the quasi-fixed point conditions shows that the mass of
the lightest Higgs boson in this case does not exceed . It
means that a substantial part of the parameter space of the MSSM is practically
excluded by existing experimental data from LEP II. In the NMSSM the upper
bound on the lightest Higgs boson mass reaches its maximum in the strong Yukawa
coupling regime, when Yukawa constants are considerably larger the gauge ones
on the Grand Unification scale. In this paper a particle spectrum in a simple
modification of NMSSM which leads to a self-consistent solution in the
considered region of the parameter space is studied. This model allows one to
get even for comparatively low values of . For an analysis of the Higgs boson spectrum and neutralino spectrum a
method for diagonalisation of mass matrices proposed formerly is used. The mass
of the lightest Higgs boson in this model does not exceed .Comment: 34 pages, 5 figures included, LaTeX 2
A novel series solution to the renormalization group equation in QCD
Recently, the QCD renormalization group (RG) equation at higher orders in
MS-like renormalization schemes has been solved for the running coupling as a
series expansion in powers of the exact 2-loop order coupling. In this work, we
prove that the power series converges to all orders in perturbation theory.
Solving the RG equation at higher orders, we determine the running coupling as
an implicit function of the 2-loop order running coupling. Then we analyze the
singularity structure of the higher order coupling in the complex 2-loop
coupling plane. This enables us to calculate the radii of convergence of the
series solutions at the 3- and 4-loop orders as a function of the number of
quark flavours . In parallel, we discuss in some detail the
singularity structure of the coupling at the 3- and 4-loops in
the complex momentum squared plane for . The
correspondence between the singularity structure of the running coupling in the
complex momentum squared plane and the convergence radius of the series
solution is established. For sufficiently large values, we find
that the series converges for all values of the momentum squared variable
. For lower values of , in the scheme,
we determine the minimal value of the momentum squared above
which the series converges. We study properties of the non-power series
corresponding to the presented power series solution in the QCD Analytic
Perturbation Theory approach of Shirkov and Solovtsov. The Euclidean and
Minkowskian versions of the non-power series are found to be uniformly
convergent over whole ranges of the corresponding momentum squared variables.Comment: 29 pages,LateX file, uses IOP LateX class file, 2 figures, 13 Tables.
Formulas (4)-(7) and Table 1 were relegated to Appendix 1, some notations
changed, 2 footnotes added. Clarifying discussion added at the end of Sect.
3, more references and acknowledgments added. Accepted for publication in
Few-Body System
Chiral symmetry breaking in gauged model in curved spacetime
Using the renormalization group (RG) approach and the equivalency between the
class of gauge-Higgs-Yukawa models and the gauged Nambu-Jona-Lasinio (NJL)
model, we study the gauged NJL model in curved space-time. The behaviour of the
scalar-gravitational coupling constant in both theories is discussed.
The RG improved effective potential of gauged NJL model in curved spacetime is
found. The curvature at which chiral symmetry in the gauged NJL model is broken
is obtained explicitly in a remarkably simple form. The powerful RG improved
effective potential formalizm leads to the same results as ladder
Schwinger-Dyson equations which have not been formulated yet in curved
spacetime what opens new possibilities in the study of GUTs and NJL-like models
in curved spacetime
Four Fermion Field Theories and the Chern-Simons Field: A Renormalization Group Study
In (2+1) dimensions, we consider the model of a flavor, two-component
fermionic field interacting through a Chern-Simons field besides a four fermion
self-interaction which consists of a linear combination of the Gross-Neveu and
Thirring like terms. The four fermion interaction is not perturbatively
renormalizable and the model is taken as an effective field theory in the
region of low momenta. Using Zimmerman procedure for reducing coupling
constants, it is verified that, for small values of the Chern-Simons parameter,
the origin is an infrared stable fixed point but changes to ultraviolet stable
as becomes bigger than a critical . Composite operators are
also analyzed and it is shown that a specific four fermion interaction has an
improved ultraviolet behavior as increases.Comment: 9 pages, revte
Modular Cosmology
An exploratory study of the cosmology of moduli in string theory. Moduli are
argued to be natural inflaton fields and lead to a robust inflationary
cosmology in which inflation takes place at the top of domain walls. The
amplitude of microwave background fluctuations constrains the dynamics
responsible for inflation to take place at a higher scale than supersymmetry
breaking. Models explaining this difference in scales and also preventing the
dilaton from running to infinity are proposed. The problem of dilaton
domination of the energy density of the universe is not resolved.Comment: harvmac, 37 pages, 3 figures as a separate uuencoded tar fil
- …