28,838 research outputs found

### A Strategy for a Vanishing Cosmological Constant in the Presence of Scale Invariance Breaking

Recent work has shown that complex quantum field theory emerges as a
statistical mechanical approximation to an underlying noncommutative operator
dynamics based on a total trace action. In this dynamics, scale invariance of
the trace action becomes the statement $0=Re Tr T_{\mu}^{\mu}$, with $T_{\mu
\nu}$ the operator stress energy tensor, and with $Tr$ the trace over the
underlying Hilbert space. We show that this condition implies the vanishing of
the cosmological constant and vacuum energy in the emergent quantum field
theory. However, since the scale invariance condition does not require the
operator $T_{\mu}^{\mu}$ to vanish, the spontaneous breakdown of scale
invariance is still permitted.Comment: Second award in the Gravity Research Foundation Essay Competition for
1997; to appear in General Relativity and Gravitation. Plain Tex, no figure

### Efficient Simulation of Quantum State Reduction

The energy-based stochastic extension of the Schrodinger equation is a rather
special nonlinear stochastic differential equation on Hilbert space, involving
a single free parameter, that has been shown to be very useful for modelling
the phenomenon of quantum state reduction. Here we construct a general closed
form solution to this equation, for any given initial condition, in terms of a
random variable representing the terminal value of the energy and an
independent Brownian motion. The solution is essentially algebraic in
character, involving no integration, and is thus suitable as a basis for
efficient simulation studies of state reduction in complex systems.Comment: 4 pages, No Figur

### Structure of Fluctuation Terms in the Trace Dynamics Ward Identity

We give a detailed analysis of the anti-self-adjoint operator contribution to
the fluctuation terms in the trace dynamics Ward identity. This clarifies the
origin of the apparent inconsistency between two forms of this identity
discussed in Chapter 6 of our recent book on emergent quantum theory.Comment: TeX; 14 pages. Dedicated to Rafael Sorkin on the occasion of his 60th
birthda

### Measurement of photons via conversion pairs in \sqrt{s_{NN}} = 200 GeV Au+Au collisions with the PHENIX experiment at RHIC

Thermal photons can provide information on the temperature of the new state
of matter created at RHIC. In the p_T region of 1--3 GeV/c thermal photons are
expected to be the dominant direct photon source. Therefore, a possible excess
compared to a pure decay photon signal due to a thermal photon contribution
should be seen in the double ratio
(\gamma/\gamma(\pi^{0}))_{Measured}/(\gamma/\gamma(\pi^{0}))_{Simulated}, if
sufficient accuracy can be reached. We present a method to reconstruct direct
photons by measuring e^{+}e^{-}--pairs from external photon conversions.Comment: 4 pages, 7 figures. To appear in the proceedings of Hot Quarks 2006:
Workshop for Young Scientists on the Physics of Ultrarelativistic
Nucleus-Nucleus Collisions, Villasimius, Italy, 15-20 May 200

### No Eigenvalue in Finite Quantum Electrodynamics

We re-examine Quantum Electrodynamics (QED) with massless electron as a
finite quantum field theory as advocated by Gell-Mann-Low, Baker-Johnson,
Adler, Jackiw and others. We analyze the Dyson-Schwinger equation satisfied by
the massless electron in finite QED and conclude that the theory admits no
nontrivial eigenvalue for the fine structure constant.Comment: 13 pages, Late

### Femtoscopic results in Au+Au and p+p from PHENIX at RHIC

Ultra-relativistic gold-gold and proton-proton collisions are investigated in
the experiments of the Relativistic Heavy Ion Collider (RHIC). In the last
several years large amount of results were revealed about the matter created in
these collisions. The latest PHENIX results for femtoscopy and correlations are
reviewed in this paper. Bose-Einstein correlations of charged kaons in 200 GeV
Au+Au collisions and of charged pions in 200 GeV p+p collisions are shown. They
are both compatible with previous measurements of charged pions in gold-gold
collisions, with respect to transverse mass or number of participants scaling.Comment: Talk given at the VI Workshop on Particle Correlations and
Femtoscopy, Kiev, September 14-18, 2010. 6 pages, 4 figures. This work was
supported by the OTKA grant NK73143 and M. Csanad's Bolyai scholarshi

### Response to the Comment by G. Emch on Projective Group Representations in Quaternionic Hilbert Space

We discuss the differing definitions of complex and quaternionic projective
group representations employed by us and by Emch. The definition of Emch
(termed here a strong projective representation) is too restrictive to
accommodate quaternionic Hilbert space embeddings of complex projective
representations. Our definition (termed here a weak projective representation)
encompasses such embeddings, and leads to a detailed theory of quaternionic, as
well as complex, projective group representations.Comment: 8 pages, Revtex, no figure

### Nuclear modification at sqrt{s_{NN}}=17.3 GeV, measured at NA49

Transverse momentum spectra up to 4.5 GeV/c were measured around midrapidity
in Pb+Pb reactions at sqrt{s_{NN}}=17.3 GeV, for pi^{+/-}, p, pbar and K^{+/-},
by the NA49 experiment. The nuclear modification factors R_{AA}, R_{AA/pA} and
R_{CP} were extracted and are compared to RHIC results at sqrt{s_{NN}}=200 GeV.
The modification factor R_{AA} shows a rapid increase with transverse momentum
in the covered region. The modification factor R_{CP} shows saturation well
below unity in the pi^{+/-} channel. The extracted R_{CP} values follow the 200
GeV RHIC results closely in the available transverse momentum range for all
particle species. For pi^{+/-} above 2.5 GeV/c transverse momentum, the
measured suppression is smaller than that observed at RHIC. The nuclear
modification factor R_{AA/pA} for pi^{+/-} stays well below unity.Comment: Proceedings of Quark Matter 2008 conferenc

### Algebraic and geometric aspects of generalized quantum dynamics

\noindent We briefly discuss some algebraic and geometric aspects of the
generalized Poisson bracket and non--commutative phase space for generalized
quantum dynamics, which are analogous to properties of the classical Poisson
bracket and ordinary symplectic structure.Comment: 10pages,revtex, IASSNSHEP-93/5

### Direct photons measured by the PHENIX experiment at RHIC

Results from the PHENIX experiment at RHIC on direct photon production in
p+p, d+Au, and Au+Au collisions at sqrt(s_NN) = 200 GeV are presented. In p+p
collisions, direct photon production at high p_T behaves as expected from
perturbative QCD calculations. The p+p measurement serves as a baseline for
direct photon production in Au+Au collisions. In d+Au collisions, no effects of
cold nuclear matter are found within the large uncertainty of the measurement.
In Au+Au collisions, the production of high p_T direct photons scales as
expected for particle production in hard scatterings. This supports jet
quenching models, which attribute the suppression of high p_T hadrons to the
energy loss of fast partons in the medium produced in the collision. Low p_T
direct photons, measured via e+e- pairs with small invariant mass, are possibly
related to the production of thermal direct photons.Comment: 5 pages, 5 figures, Proceedings of the Hot Quarks 2006 Workshop for
young scientists on the physics of ultra-relativistic nucleus-nucleus
collisions, Villasimius, Sardinia, Italy, May 15--20, 200

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