1,979 research outputs found
The Transition Amplitude for 2T Physics
We present the transition amplitude for a particle moving in a space with two
times and D space dimensions having a Sp(2,R) local symmetry and an SO(D,2)
rigid symmetry. It was obtained from the BRST-BFV quantization with a unique
gauge choice. We show that by constraining the initial and final points of this
amplitude to lie on some hypersurface of the D+2 space the resulting amplitude
reproduces well known systems in lower dimensions. This provides an alternative
physical interpretation for two times physics which is derived in a single
framework.Comment: 4 pages, typos corrected, references adde
Vacuum fluctuations in a supersymmetric model in FRW spacetime
We study a noninteracting supersymmetric model in an expanding FRW spacetime.
A soft supersymmetry breaking induces a nonzero contribution to the vacuum
energy density. A short distance cutoff of the order of Planck length provides
a scale for the vacuum energy density comparable with the observed cosmological
constant. Assuming the presence of a dark energy substance in addition to the
vacuum fluctuations of the field an effective equation of state is derived in a
selfconsistent approach. The effective equation of state is sensitive to the
choice of the cut-off but no fine tuning is needed.Comment: 19 pages, accepted for publication in Phys. Rev.
Asymptotic Symmetries of Rindler Space at the Horizon and Null Infinity
We investigate the asymptotic symmetries of Rindler space at null infinity
and at the event horizon using both systematic and ad hoc methods. We find that
the approaches that yield infinite-dimensional asymptotic symmetry algebras in
the case of anti-de Sitter and flat spaces only give a finite-dimensional
algebra for Rindler space at null infinity. We calculate the charges
corresponding to these symmetries and confirm that they are finite, conserved,
and integrable, and that the algebra of charges gives a representation of the
asymptotic symmetry algebra. We also use relaxed boundary conditions to find
infinite-dimensional asymptotic symmetry algebras for Rindler space at null
infinity and at the event horizon. We compute the charges corresponding to
these symmetries and confirm that they are finite and integrable. We also
determine sufficient conditions for the charges to be conserved on-shell, and
for the charge algebra to give a representation of the asymptotic symmetry
algebra. In all cases, we find that the central extension of the charge algebra
is trivial.Comment: 37 pages, 4 figures. Version 3: New Section 5 adde
Neutrino oscillations in a Robertson-Walker Universe with space time foam
In Phys. Rev. D77 (2008) 105001, we have studied decoherence models for
flavour oscillations in four-dimensional stochastically fluctuating space times
and discussed briefly the sensitivity of current terrestrial and astrophysical
neutrino experiments to such models. In this addendum we extend these results
to incorporate the effects due to the expansion of the Universe, so that our
analysis can be useful in studies of extragalactic high-energy neutrinos, such
as those coming from Gamma Ray Bursts at cosmological distances. Unfortunately
for some microscopic models of foam, constructed in the string theory
framework, we arrive at pessimistic conclusions about the detectability of the
decoherence effects via flavour oscillation meaurements.Comment: Addendum to Phys. Rev. D77 (2008) 10500
Spacetime Structure of an Evaporating Black Hole in Quantum Gravity
The impact of the leading quantum gravity effects on the dynamics of the
Hawking evaporation process of a black hole is investigated. Its spacetime
structure is described by a renormalization group improved Vaidya metric. Its
event horizon, apparent horizon, and timelike limit surface are obtained taking
the scale dependence of Newton's constant into account. The emergence of a
quantum ergosphere is discussed. The final state of the evaporation process is
a cold, Planck size remnant.Comment: 23 pages, BibTeX, revtex4, 7 figure
Accelerated Detectors and Temperature in (Anti) de Sitter Spaces
We show, in complete accord with the usual Rindler picture, that detectors
with constant acceleration in de Sitter (dS) and Anti de Sitter (AdS)
spaces with cosmological constants measure temperatures , the detector "5-acceleration" in the
embedding flat 5-space. For dS, this recovers a known result; in AdS, where
is negative, the temperature is well defined down to the critical
value , again in accord with the underlying kinematics. The existence
of a thermal spectrum is also demonstrated for a variety of candidate wave
functions in AdS backgrounds.Comment: Latex +2 Fi
Flavour-Condensate-induced Breaking of Supersymmetry in Free Wess-Zumino Fluids
Recently we argued that a particular model of string-inspired quantum
space-time foam (D-foam) may induce oscillations and mixing among flavoured
particles. As a result, rather than the mass-eigenstate vacuum, the correct
ground state to describe the underlying dynamics is the flavour vacuum,
proposed some time ago by Blasone and Vitiello as a description of quantum
field theories with mixing. At the microscopic level, the breaking of
target-space supersymmetry is induced in our space-time foam model by the
relative transverse motion of brane defects. Motivated by these results, we
show that the flavour vacuum, introduced through an inequivalent representation
of the canonical (anti-) commutation relations, provides a vehicle for the
breaking of supersymmetry (SUSY) at a low-energy effective field theory level;
on considering the flavour-vacuum expectation value of the energy-momentum
tensor and comparing with the form of a perfect relativistic fluid, it is found
that the bosonic sector contributes as dark energy while the fermion
contribution is like dust. This indicates a strong and novel breaking of SUSY,
of a non-perturbative nature, which may characterize the low energy field
theory of certain quantum gravity models.Comment: Discussion added in sections II and IV on quantum-gravity induced
flavour mixing, references added, conclusions unchange
Vacuum entanglement enhancement by a weak gravitational field
Separate regions in space are generally entangled, even in the vacuum state.
It is known that this entanglement can be swapped to separated Unruh-DeWitt
detectors, i.e., that the vacuum can serve as a source of entanglement. Here,
we demonstrate that, in the presence of curvature, the amount of entanglement
that Unruh-DeWitt detectors can extract from the vacuum can be increased.Comment: 6 pages, 1 figur
Growth inhibition of cytosolic Salmonella by caspase-1 and caspase-11 precedes host cell death
Sensing bacterial products in the cytosol of mammalian cells by NOD-like receptors leads to the activation of caspase-1 inflammasomes, and the production of the pro-inflammatory cytokines interleukin (IL)-18 and IL-1β. In addition, mouse caspase-11 (represented in humans by its orthologs, caspase-4 and caspase-5) detects cytosolic bacterial LPS directly. Activation of caspase-1 and caspase-11 initiates pyroptotic host cell death that releases potentially harmful bacteria from the nutrient-rich host cell cytosol into the extracellular environment. Here we use single cell analysis and time-lapse microscopy to identify a subpopulation of host cells, in which growth of cytosolic Salmonella Typhimurium is inhibited independently or prior to the onset of cell death. The enzymatic activities of caspase-1 and caspase-11 are required for growth inhibition in different cell types. Our results reveal that these proteases have important functions beyond the direct induction of pyroptosis and proinflammatory cytokine secretion in the control of growth and elimination of cytosolic bacteria
Contact Term, its Holographic Description in QCD and Dark Energy
In this work we study the well known contact term, which is the key element
in resolving the so-called problem in QCD. We study this term using
the dual Holographic Description. We argue that in the dual picture the contact
term is saturated by the D2 branes which can be interpreted as the tunnelling
events in Minkowski space-time. We quote a number of direct lattice results
supporting this identification. We also argue that the contact term receives a
Casimir -like correction \sim (\Lqcd R)^{-1} rather than naively expected
\exp(-\Lqcd R) when the Minkowski space-time is replaced by
a large but finite manifold with a size . Such a behaviour is consistent
with other QFT-based computations when power like corrections are due to
nontrivial properties of topological sectors of the theory. In holographic
description such a behaviour is due to massless Ramond-Ramond (RR) field living
in the bulk of multidimensional space when power like corrections is a natural
outcome of massless RR field. In many respects the phenomenon is similar to the
Aharonov -Casher effect when the "modular electric field" can penetrate into a
superconductor where the electric field is exponentially screened. The role of
"modular operator" from Aharonov -Casher effect is played by large gauge
transformation operator in 4d QCD, resulting the transparency of the
system to topologically nontrivial pure gauge configurations. We discuss some
profound consequences of our findings. In particular, we speculate that a slow
variation of the contact term in expanding universe might be the main source of
the observed Dark Energy.Comment: Final version to appear in Phys. Rev. D. Comments added on
interpretation of the "topological Casimir effect" from 5d viewpoint where it
can be thought as conventional Casimir effec
- …