8,594 research outputs found
N=2 Conformal Superspace in Four Dimensions
We develop the geometry of four dimensional N=2 superspace where the entire
conformal algebra of SU(2,2|2) is realized linearly in the structure group
rather than just the SL(2,C) x U(2)_R subgroup of Lorentz and R-symmetries,
extending to N=2 our prior result for N=1 superspace. This formulation
explicitly lifts to superspace the existing methods of the N=2 superconformal
tensor calculus; at the same time the geometry, when degauged to SL(2,C) x
U(2)_R, reproduces the existing formulation of N=2 conformal supergravity
constructed by Howe.Comment: 43 pages; v2 references added, acknowledgments update
M Theory As A Matrix Model: A Conjecture
We suggest and motivate a precise equivalence between uncompactified eleven
dimensional M-theory and the N = infinity limit of the supersymmetric matrix
quantum mechanics describing D0-branes. The evidence for the conjecture
consists of several correspondences between the two theories. As a consequence
of supersymmetry the simple matrix model is rich enough to describe the
properties of the entire Fock space of massless well separated particles of the
supergravity theory. In one particular kinematic situation the leading large
distance interaction of these particles is exactly described by supergravity .
The model appears to be a nonperturbative realization of the holographic
principle. The membrane states required by M-theory are contained as
excitations of the matrix model. The membrane world volume is a noncommutative
geometry embedded in a noncommutative spacetime.Comment: Typo and tex error corrected. 41 pages, harvma
Weighted Supermembrane Toy Model
A weighted Hilbert space approach to the study of zero-energy states of
supersymmetric matrix models is introduced. Applied to a related but
technically simpler model, it is shown that the spectrum of the corresponding
weighted Hamiltonian simplifies to become purely discrete for sufficient
weights. This follows from a bound for the number of negative eigenvalues of an
associated matrix-valued Schr\"odinger operator.Comment: 18 pages, 2 figures; to appear in Lett. Math. Phys
An active asteroid belt causing the UX Ori phenomenon in RZ Psc
We report the discovery of mid-infrared excess emission in the young object
RZ Psc. The excess constitutes ~8% of its Lbol, and is well fit by a single
500K black-body implying a dust free region within 0.7AU for optically thick
dust. The object displays dust obscuration events (UXOR behaviour) with a
time-scale that suggests dusty material on orbits of 0.5AU. We also report a
12.4 year cyclical photometric variability which can be interpreted as due to
perturbations in the dust distribution. The system is characterized by a high
inclination, marginal extinction (during bright photometric states), a single
temperature for the warm dust, and an age estimate which puts the star beyond
the formation stage. We propose that the dust occultation events present a
dynamical view of an active asteroid belt whose collisional products
sporadically obscure the central star.Comment: Accepted for A&A letter
Nilpotent Marsh and SUSY QM
We consider the nilpotent additions to classical trajectories in
supersymmetric and nonsupersymmetric theories. The condition of anilpotence of
action on some generalized solutions leads to the Witten supersymmetric
Lagrangian. The condition of anilpotence of topological charge is the same as
one of superpotential with spontaneous broken supersymmetry. We should vanish
half of Grassmann constants of integration, because in this case only we obtain
the same number of normalized bosonic and fermionic zero modes.Comment: 8 pages, Latex 2.09. Talk given at the conference in memory of V.I.
Ogievetski, Dubna, July, 1997. To be published in the Proceeding
Refined Algebraic Quantization in the oscillator representation of SL(2,R)
We investigate Refined Algebraic Quantization (RAQ) with group averaging in a
constrained Hamiltonian system with unreduced phase space T^*R^4 and gauge
group SL(2,R). The reduced phase space M is connected and contains four
mutually disconnected `regular' sectors with topology R x S^1, but these
sectors are connected to each other through an exceptional set where M is not a
manifold and where M has non-Hausdorff topology. The RAQ physical Hilbert space
H_{phys} decomposes as H_{phys} = (direct sum of) H_i, where the four subspaces
H_i naturally correspond to the four regular sectors of M. The RAQ observable
algebra A_{obs}, represented on H_{phys}, contains natural subalgebras
represented on each H_i. The group averaging takes place in the oscillator
representation of SL(2,R) on L^2(R^{2,2}), and ensuring convergence requires a
subtle choice for the test state space: the classical analogue of this choice
is to excise from M the exceptional set while nevertheless retaining
information about the connections between the regular sectors. A quantum theory
with the Hilbert space H_{phys} and a finitely-generated observable subalgebra
of A_{obs} is recovered through both Ashtekar's Algebraic Quantization and
Isham's group theoretic quantization.Comment: 30 pages, REVTeX v3.1 with amsfonts. (v4: Published version.
Supermembranes and Super Matrix Models
We review recent developments in the theory of supermembranes and their
relation to matrix models.Comment: Invited lecture presented at the Corfu Workshop, September 20 - 26,
1998, of the TMR Project "Quantum Aspects of Gauge Theories, Supersymmetry
and Unification" (ERBFMRXCT96-0045), to appear in the proceedings. Latex 41
p
Black hole entropy functions and attractor equations
The entropy and the attractor equations for static extremal black hole
solutions follow from a variational principle based on an entropy function. In
the general case such an entropy function can be derived from the reduced
action evaluated in a near-horizon geometry. BPS black holes constitute special
solutions of this variational principle, but they can also be derived directly
from a different entropy function based on supersymmetry enhancement at the
horizon. Both functions are consistent with electric/magnetic duality and for
BPS black holes their corresponding OSV-type integrals give identical results
at the semi-classical level. We clarify the relation between the two entropy
functions and the corresponding attractor equations for N=2 supergravity
theories with higher-derivative couplings in four space-time dimensions. We
discuss how non-holomorphic corrections will modify these entropy functions.Comment: 21 pages,LaTeX,minor change
Transverse nucleon structure and diagnostics of hard parton-parton processes at LHC
We propose a new method to determine at what transverse momenta particle
production in high-energy pp collisions is governed by hard parton-parton
processes. Using information on the transverse spatial distribution of partons
obtained from hard exclusive processes in ep/gamma p scattering, we evaluate
the impact parameter distribution of pp collisions with a hard parton-parton
process as a function of p_T of the produced parton (jet). We find that the
average pp impact parameters in such events depend very weakly on p_T in the
range 2 < p_T < few 100 GeV, while they are much smaller than those in
minimum-bias inelastic collisions. The impact parameters in turn govern the
observable transverse multiplicity in such events (in the direction
perpendicular to the trigger particle or jet). Measuring the transverse
multiplicity as a function of p_T thus provides an effective tool for
determining the minimum p_T for which a given trigger particle originates from
a hard parton-parton process. Additional tests of the proposed geometric
correlations are possible by measuring the dependence on the trigger rapidity.
Various strategies for implementing this method are outlined.Comment: 9 pages, 6 figure
Reconnaissance of the TRAPPIST-1 exoplanet system in the Lyman- line
The TRAPPIST-1 system offers the opportunity to characterize terrestrial,
potentially habitable planets orbiting a nearby ultracool dwarf star. We
performed a four-orbit reconnaissance with the Space Telescope Imaging
Spectrograph onboard the Hubble Space Telescope to study the stellar emission
at Lyman-, to assess the presence of hydrogen exospheres around the two
inner planets, and to determine their UV irradiation. We detect the
Lyman- line of TRAPPIST-1, making it the coldest exoplanet host star
for which this line has been measured. We reconstruct the intrinsic line
profile, showing that it lacks broad wings and is much fainter than expected
from the stellar X-ray emission. TRAPPIST-1 has a similar X-ray emission as
Proxima Cen but a much lower Ly- emission. This suggests that
TRAPPIST-1 chromosphere is only moderately active compared to its transition
region and corona. We estimated the atmospheric mass loss rates for all
planets, and found that despite a moderate extreme UV emission the total XUV
irradiation could be strong enough to strip the atmospheres of the inner
planets in a few billions years. We detect marginal flux decreases at the times
of TRAPPIST-1b and c transits, which might originate from stellar activity, but
could also hint at the presence of extended hydrogen exospheres. Understanding
the origin of these Lyman- variations will be crucial in assessing the
atmospheric stability and potential habitability of the TRAPPIST-1 planets.Comment: Published in A&A as a Letter to the Edito
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