5 Phenomenology of Analogue Models

Of course, the entire motivation for looking at analogue models is to be able to learn more physics. One could start studying analogue models with the idea of seeing whether it is possible (either theoretically or in practice) to reproduce in the laboratory various gravitational phenomena whose real existence in nature cannot be currently checked. These are phenomena that surpass our present (and foreseeable) observational capabilities, but yet, we believe in their existence because it follows from seemingly strong theoretical arguments within the standard frameworks of general relativity and field theory in curved space. However, the interest of this approach is not merely to reproduce these gravitational phenomena in some formal analogue model, but to see which departures from the ideal case show up in real analogue models, and to analyse whether similar deviations are likely to appear in real gravitational systems.

When one thinks about emergent gravitational features in condensed-matter systems, one immediately realises that these features only appear in the low-energy regime of the analogue systems. When these systems are probed at high energies (short length scales) the effective geometrical description of the analogue models break down, as one starts to be aware that the systems are actually composed of discrete pieces (atoms and molecules). This scenario is quite similar to what one expects to happen with our geometrical description of the Universe, when explored with microscopic detail at the Planck scale.

That is, the study of analogue models of general relativity is giving us insights as to how the standard theoretical picture of different gravitational phenomena could change when taking into account additional physical knowledge coming from the existence of an underlying microphysical structure. Quite robustly, these studies are telling us already that the first deviations from the standard general relativity picture can be encoded in the form of high-energy violations of Lorentz invariance in particle dispersion relations. Beyond these first deviations, the analogue models of general relativity provide well-understood examples (the underlying physics is well known) in which a description in terms of fields in curved spacetimes shows up as a low-energy-regime emergent phenomena.

The analogue models are being used to shed light on these general questions through a number of specific routes. Let us now turn to discussing several specific physics issues that are being analysed from this perspective.

 5.1 Hawking radiation
  5.1.1 Basics
  5.1.2 UV robustness
  5.1.3 General conditions for Hawking radiation
  5.1.4 Source of the Hawking quanta
  5.1.5 Which surface gravity?
  5.1.6 How to detect Hawking radiation: Correlations
  5.1.7 Open issues
  5.1.8 Solid state and lattice models
  5.1.9 Analogue spacetimes as background gestalt
 5.2 Dynamical stability of horizons
  5.2.1 Classical stability of the background (no MDR)
  5.2.2 Semiclassical stability of the background (no MDR)
  5.2.3 Classical stability of the background (MDR in BECs)
  5.2.4 Black holes, white holes, and rings
 5.3 Super-radiance
 5.4 Cosmological particle production
 5.5 Bose novae: an example of the reverse flow of information?
 5.6 Romulan cloaking devices
 5.7 Going further

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