Physics meets philosophy at the Planck scale: Contemporary
... in the business of providing an accurate picture of reality in any deeper sense. Since
there are currently no observations demanding a quantum gravitational theory, it
might be thought that advocates of such a position would view the endeavour as
empty and misguided speculation, perhaps of formal in ...
Approaches to Quantum Gravity
... version, i.e. spin foam models). Alongside them, we have various (and rather different in both spirit and techniques used) discrete approaches, represented here
by simplicial quantum gravity, in particular the recent direction of causal dynamical triangulations, quantum Regge calculus, and the “cons ...
Gauge symmetries in Quantum Gravity and String Theory
... This thesis explores the spectrum of states charged under global and gauge symmetries in String Theory, and the constraints that they pose on specific phenomenological models. On one hand, we use supercritical theories (those with more than
10 or 26 dimensions) to embed discrete gauge symmetries of ...
Lectures on Conformal Field Theory arXiv:1511.04074v2 [hep
... Yet another familiar theory is the classical λφ4 theory in d = 4 dimensions with equation
∂ 2 φ = λφ3 /3!
Even with interactions, however, the associated Lagrangians describe massless fields.
This is because a theory cannot be conformally invariant if the Lagrangian has some
mass parameter ...
- Free Documents
... of work that followed, it became clear that a useful framework for under
standing this situation is Atiyahs axiomatic description of a topological
quantum eld theory, or TQFT.
On the other hand, at about the same time as Jones initial discov
ery, Ashtekar discovered a reformulation of general relati ...
Kuhn Losses Regained: Van Vleck from Spectra to
... By the time he wrote his article in Chemical Reviews, Van Vleck had come to recognize
that a strong argument against the old and in favor of the new quantum theory could be
found in the theory of susceptibilities, a subject of marginal interest during the reign of
the old quantum theory. As he wrot ...
gravity theory based on mass–energy equivalence
... The mass density field differs from those in current theories of gravity
since it includes negative values and must be integrated to infinity. We interpreted the negative values as resulting from rest mass waves and kinetic
energy waves in the FS. The speed of an object is defined relative to the FS ...
Spin Foam Models of Quantum Spacetime
... Relativity in terms of the Ashtekar variables . In recent years many different
approaches on the non-perturbative and background-independent side have been
converging to the formalism of the so-called spin foams [13, 14, 15], and this class
of models in the subject of this thesis.
Why do we want ...
Axial gravity, massless fermions and trace anomalies
... subject has been already treated in [1, 2]. The second, to our best knowledge, is new. The
motivation for reconsidering the former is to clarify the theoretical background underlying the
approach and complete the calculation of the anomaly, also in view of more recent results,
. For some aspects ...
... Group Field Theories: spacetime from quantum discreteness to an amergent continuum – p. 4/3
models, simplicial QG,...
From Principles to Diagrams
... Kähler action plus cosmological term. This brings in the radii of spheres S 2 (M 4 ) and S 2 (CP2 )
associated with the twistors space of M 4 and CP2 . For S(CP2 ) the radius is of order CP2 radius
R. R(S 2 (M 4 )) could be of the order of Planck length lP , which would thus become purely classical ...
The AdS 3/CFT2 correspondence in black hole physics
... with the current methods, the only familiar case of a black hole that can be treated strictly is
the extremal Reissner-Nordstrøm solution when embedded in an N ≥ 2 supergravity theory,
since it is known to support one Killing spinor. This has been extended to near extremal cases
as well, but a full ...
... make up our universe. It also gives the only presently credible explanation for the value
of the cosmological constant although, in fairness, I should add that the explanation is
so distasteful to some that the community is rather amusingly split between whether
this is a good thing or a bad thing. ...
Geophysics :: 1. Gravity methods
... the ellipsoid (the difference between the geocentric and geographic latitude is very small, reaching its maximum
a latitude of 45° and it amounts to 0.19°). Applied geophysicists have used this relationship for the determination
gravity distribution at the sea level and for normal correction. The fi ...
String Theory - damtp - University of Cambridge
... Reason 2. String theory may be the theory of quantum gravity
With broad brush, string theory looks like an extremely good candidate to describe the
real world. At low-energies it naturally gives rise to general relativity, gauge theories,
scalar fields and chiral fermions. In other words, it contai ...
"Loop Quantum Gravity" (Rovelli)
... For a relativist, on the other hand, the idea of a fundamental description of gravity in terms of
physical excitations over a background space sounds physically wrong. The key lesson learned from
general relativity is that there is no background metric space over which physics happens (except,
of co ...
Haag`s Theorem in Renormalisable Quantum Field Theories
... divergences encountered there were cured by a finite number of subtractions, once the appropriate counterterms had been identified [GliJaf68, GliJaf70].
• Fourth, however, these problems exacerbated to serious and to this day unsurmountable obstructions as soon as the realm of renormalisable theorie ...
How do you divide your (two dimensional) time? .1in SLE, CLE, the
... “There are methods and formulae in science, which serve as masterkeys to many apparently different problems. The resources of such things
have to be refilled from time to time. In my opinion at the present time
we have to develop an art of handling sums over random surfaces. These
sums replace the ...
Discrete Approaches to Quantum Gravity in Four Dimensions
... of quantum gravity in four dimensions via an intermediate discretization. I
will only discuss models with some concrete implementation of the dynamics of
Einstein’s theory, Lagrangian or Hamiltonian.
One way of tackling the quantization problem non-perturbatively is to use
discrete methods, in analo ...
The Mathematics of the Casimir Effect
... On the Whole, Divergent Series are the Works of the Devil and it’s a
Shame that one dares base any Demonstration upon them. You can get
whatever result you want when you use them, and they have given rise to
so many Disasters and so many Paradoxes. Can anything more horrible
be conceived than to hav ...
Effective Field Theory
... are integrated out from the action. One gets in this way a string of nonrenormalizable interactions among the light states, which can be organized
as an expansion in powers of energy/Λ. The information on the heavier
degrees of freedom is then contained in the couplings of the resulting lowenergy La ...
The AdS/CMT manual for plumbers and electricians
... Eddington had a thorough understanding of the theory itself, as required to design the observations putting Einstein
on the real axis of empirical reality. Perhaps more importantly, his obsessive attitudes were required to generate the
resilience to bring the business side of this affair to a happy ...
Asymptotic safety in quantum gravity
Asymptotic safety (sometimes also referred to as nonperturbative renormalizability) is a concept in quantum field theory which aims at finding a consistent and predictive quantum theory of the gravitational field. Its key ingredient is a nontrivial fixed point of the theory's renormalization group flow which controls the behavior of the coupling constants in the ultraviolet (UV) regime and renders physical quantities safe from divergences. Although originally proposed by Steven Weinberg to find a theory of quantum gravity, the idea of a nontrivial fixed point providing a possible UV completion can be applied also to other field theories, in particular to perturbatively nonrenormalizable ones. In this respect, it is similar to Quantum triviality.The essence of asymptotic safety is the observation that nontrivial renormalization group fixed points can be used to generalize the procedure of perturbative renormalization. In an asymptotically safe theory the couplings do not need to be small or tend to zero in the high energy limit but rather tend to finite values: they approach a nontrivial UV fixed point. The running of the coupling constants, i.e. their scale dependence described by the renormalization group (RG), is thus special in its UV limit in the sense that all their dimensionless combinations remain finite. This suffices to avoid unphysical divergences, e.g. in scattering amplitudes. The requirement of a UV fixed point restricts the form of the bare action and the values of the bare coupling constants, which become predictions of the asymptotic safety program rather than inputs.As for gravity, the standard procedure of perturbative renormalization fails since Newton's constant, the relevant expansion parameter, has negative mass dimension rendering general relativity perturbatively nonrenormalizable. This has driven the search for nonperturbative frameworks describing quantum gravity, including asymptotic safety which — in contrast to other approaches—is characterized by its use of quantum field theory methods, without depending on perturbative techniques, however. At the present time, there is accumulating evidence for a fixed point suitable for asymptotic safety, while a rigorous proof of its existence is still lacking.