Abstracts for October-November 2015

  • High energy particle colliders have been in the forefront of particle physics for more than three decades. At present the near term US, European and international strategies of the particle physics community are centered on full exploitation of the physics potential of the Large Hadron Collider (LHC) through its high-luminosity upgrade (HL-LHC). A number of the next generation collider facilities have been proposed and are currently under consideration for the medium and far-future of accelerator-based high energy physics. In this paper we offer a uniform approach to evaluation of various accelerators based on the feasibility of their energy reach, performance potential and cost range.
    (H/t Sabine.) The contraction has been happening for quite some time:

    maximum c.o.m. energy has drastically slowed down since the early 1990’s and the lepton colliders even went backwards in energy to study rare processes…Moreover, the number of the colliding beam facilities in operation has dropped from 9 two decades ago to 5 now…

  • Conditions for Quantum Violation of Macroscopic Realism
    Johannes Kofler and Časlav Brukner
    Why do we not experience a violation of macroscopic realism in everyday life. Normally, no violation can be seen either because of decoherence or the restriction of coarse-grained measurements, transforming the time evolution of any quantum state into a classical time evolution of a statistical mixture. We find the sufficient condition for these classical evolutions for spin systems under coarse-grained measurements. However, there exist ‘‘nonclassical’’ Hamiltonians whose time evolution cannot be understood classically, although at every instant of time the quantum state appears as a classical mixture. We suggest that such Hamiltonians are unlikely to be realized in nature because of their high computational complexity.
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Abstracts for September 2015

I’m trying out a new type of post: a selection of abstracts I thought were particularly interesting this month (though not necessarily released this month). Some papers I’ll have read in detail, some not. I would be particularly interested in hearing commentary on them.

  • Experiments testing macroscopic quantum superpositions must be slow
    Andrea Mari, Giacomo De Palma, Vittorio Giovannetti
    We consider a thought experiment where the preparation of a macroscopically massive or charged particle in a quantum superposition and the associated dynamics of a distant test particle apparently allow for superluminal communication. We give a solution to the paradox which is based on the following fundamental principle: any local experiment, discriminating a coherent superposition from an incoherent statistical mixture, necessarily requires a minimum time proportional to the mass (or charge) of the system. For a charged particle, we consider two examples of such experiments, and show that they are both consistent with the previous limitation. In the first, the measurement requires to accelerate the charge, that can entangle with the emitted photons. In the second, the limitation can be ascribed to the quantum vacuum fluctuations of the electromagnetic field. On the other hand, when applied to massive particles our result provides an indirect evidence for the existence of gravitational vacuum fluctuations and for the possibility of entangling a particle with quantum gravitational radiation.
    Note that although the OTIMA matter interferometers require an amount of time proportional to the superposed mass to confirm a superposition, the proportionality constant is vastly larger than the one apparently demonstrated here.
  • In this talk we explain the elements of symplectic geometry, and sketch the proof of one of its foundational results — Gromov’s nonsqueezing theorem — using J-holomorphic curves.
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