1,287 research outputs found
Inverse Seesaw Neutrino Mass from Lepton Triplets in the U(1)_Sigma Model
The inverse seesaw mechanism of neutrino mass, i.e. m_nu =
(m_D^2/m_N^2)epsilon_L where epsilon_L is small, is discussed in the context of
the U(1)_Sigma model. This is a gauge extension of the Standard Model of
particle interactions with lepton triplets (Sigma^+,Sigma^),Sigma^-) as (Type
III) seesaw anchors for obtaining small Majorana neutrino masses.Comment: 7 pages, no figur
The Influence of World-Sheet Boundaries on Critical Closed String Theory
This paper considers interactions between closed strings and open strings
satisfying either Neumann or constant (point-like) Dirichlet boundary
conditions in a BRST formalism in the critical dimension. With Neumann
conditions this reproduces the well-known stringy version of the Higgs
mechanism. With Dirichlet conditions the open-string states correspond to
either auxiliary or Lagrange multiplier target-space fields and their coupling
to the closed-string sector leads to constraints on the closed-string spectrum.Comment: 15 pages, QMW-92-18;NI9201
The String Coupling Accelerates the Expansion of the Universe
Generic cosmological models in non-critical string theory have a
time-dependent dilaton background at a late epoch. The cosmological
deceleration parameter Q_0 is given by the square of the string coupling,
g_s^2, up to a negative sign. Hence the expansion of the Universe must
accelerate eventually, and the observed value of Q_0 coresponds to g_s^2 ~ 0.6.
In this scenario, the string coupling is asymptotically free at large times,
but its present rate of change is imperceptibly small.Comment: 7 page
Entropy of gravitating systems: scaling laws versus radial profiles
Through the consideration of spherically symmetric gravitating systems
consisting of perfect fluids with linear equation of state constrained to be in
a finite volume, an account is given of the properties of entropy at conditions
in which it is no longer an extensive quantity (it does not scale with system's
size). To accomplish this, the methods introduced by Oppenheim [1] to
characterize non-extensivity are used, suitably generalized to the case of
gravitating systems subject to an external pressure. In particular when, far
from the system's Schwarzschild limit, both area scaling for conventional
entropy and inverse radius law for the temperature set in (i.e. the same
properties of the corresponding black hole thermodynamical quantities), the
entropy profile is found to behave like 1/r, being r the area radius inside the
system. In such circumstances thus entropy heavily resides in internal layers,
in opposition to what happens when area scaling is gained while approaching the
Schwarzschild mass, in which case conventional entropy lies at the surface of
the system. The information content of these systems, even if it globally
scales like the area, is then stored in the whole volume, instead of packed on
the boundary.Comment: 16 pages, 11 figures. v2: addition of some references; the stability
of equilibrium configurations is readdresse
Fractal Holography: a geometric re-interpretation of cosmological large scale structure
The fractal dimension of large-scale galaxy clustering has been demonstrated
to be roughly from a wide range of redshift surveys. If correct,
this statistic is of interest for two main reasons: fractal scaling is an
implicit representation of information content, and also the value itself is a
geometric signature of area. It is proposed that the fractal distribution of
galaxies may thus be interpreted as a signature of holography (``fractal
holography''), providing more support for current theories of holographic
cosmologies. Implications for entropy bounds are addressed. In particular,
because of spatial scale invariance in the matter distribution, it is shown
that violations of the spherical entropy bound can be removed. This holographic
condition instead becomes a rigid constraint on the nature of the matter
density and distribution in the Universe. Inclusion of a dark matter
distribution is also discussed, based on theoretical considerations of possible
universal CDM density profiles.Comment: 13 pp, LaTeX. Revised version; to appear in JCA
Magnetic Wormholes and Vertex Operators
We consider wormhole solutions in Euclidean dimensions. A duality
transformation is introduced to derive a new action from magnetic wormhole
action of Gupta, Hughes, Preskill and Wise. The classical solution is
presented. The vertex operators corresponding to the wormhole are derived.
Conformally coupled scalars and spinors are considered in the wormhole
background and the vertex operators are computed. ( To be published in Phys.
Rev. D15)Comment: 18 pages of RevTex, preprint IP/BBSR/94-2
Symmetry Breaking at enhanced Symmetry Points
The influence of world-sheet boundary condensates on the toroidal
compactification of bosonic string theories is considered. At the special
points in the moduli space at which the closed-string theory possesses an
enhanced unbroken symmetry (where is a semi-simple product of
simply laced groups) a scalar boundary condensate parameterizes the coset
. Fluctuations around this background define an open-string
generalization of the corresponding chiral nonlinear sigma model. Tree-level
scattering amplitudes of on-shell massless states (\lq pions') reduce to the
amplitudes of the principal chiral model for the group in the low energy
limit. Furthermore, the condition for the vanishing of the renormalization
group beta function at one loop results in the familiar equation of motion for
that model. The quantum corrections to the open-string theory generate a mixing
of open and closed strings so that the coset-space pions mix with the
closed-string gauge fields, resulting in a Higgs-like breakdown of
the symmetry to the diagonal group. The case of non-oriented strings is
also discussed.Comment: 32 pages, LaTeX, 2 figures in uuencoded fil
A finite cutoff on the string worldsheet?
D-brane backgrounds are specified in closed string theories by holes with
appropriate mixed Dirichlet and Neumann boundary conditions on the string
worldsheet. As presently stated, the prescription defining D-brane backgrounds
is such that the Einstein equation is not equivalent to the condition for scale
invariance on the string worldsheet. A modified D-brane prescription is found,
that leads to the desired equivalence, while preserving all known D-brane lore.
A possible interpretation is that the worldsheet cutoff is finite. Possible
connections to recent work of Maldacena and Strominger, and Gopakumar and Vafa
are suggested.Comment: 7 pages, RevTex; v2: typos corrected, superstring calculation
included, discussion expanded - to be published in Phys.Rev.
Hologrphy and holographic dark energy model
The holographic principle is used to discuss the holographic dark energy
model. We find that the Bekenstein-Hawking entropy bound is far from saturation
under certain conditions. A more general constraint on the parameter of the
holographic dark energy model is also derived.Comment: no figures, use revtex, v2: use iop style, some typos corrected and
references updated, will appear in CQ
Combinatorics of Boundaries in String Theory
We investigate the possibility that stringy nonperturbative effects appear as
holes in the world-sheet. We focus on the case of Dirichlet string theory,
which we argue should be formulated differently than in previous work, and we
find that the effects of boundaries are naturally weighted by .Comment: 12 pages, 2 figures, LaTe
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