4,094 research outputs found
B -> D* l nu and B -> D l nu form factors in staggered chiral perturbation theory
We calculate the B -> D and B -> D* form factors at zero recoil in Staggered
Chiral Perturbation Theory. We consider heavy-light mesons in which only the
light (u, d, or s) quark is staggered; current lattice simulations generally
use a highly improved action such as the Fermilab or NRQCD action for the heavy
(b or c) quark. We work to lowest nontrivial order in the heavy quark expansion
and to one-loop in the chiral expansion. We present results for a partially
quenched theory with three sea quarks in which there are no mass degeneracies
(the "1+1+1" theory) and for a partially quenched theory in which the u and d
sea quark masses are equal (the "2+1" theory). We also present results for full
(2+1) QCD, along with a numerical estimate of the size of staggered
discretization errors. Finally, we calculate the finite volume corrections to
the form factors and estimate their numerical size in current lattice
simulations.Comment: 19 pages, 6 figures, references added, expanded discussion in Section
I
Evidence for Asymptotic Safety from Lattice Quantum Gravity
We calculate the spectral dimension for nonperturbative quantum gravity
defined via Euclidean dynamical triangulations. We find that it runs from a
value of ~3/2 at short distance to ~4 at large distance scales, similar to
results from causal dynamical triangulations. We argue that the short distance
value of 3/2 for the spectral dimension may resolve the tension between
asymptotic safety and the holographic principle.Comment: 4 pages, 2 figures. Minor typos corrected, clarifications and
reference added. Conforms with version published in PR
Exploring Euclidean Dynamical Triangulations with a Non-trivial Measure Term
We investigate a nonperturbative formulation of quantum gravity defined via
Euclidean dynamical triangulations (EDT) with a non-trivial measure term in the
path integral. We are motivated to revisit this older formulation of dynamical
triangulations by hints from renormalization group approaches that gravity may
be asymptotically safe and by the emergence of a semiclassical phase in causal
dynamical triangulations (CDT). We study the phase diagram of this model and
identify the two phases that are well known from previous work: the branched
polymer phase and the collapsed phase. We verify that the order of the phase
transition dividing the branched polymer phase from the collapsed phase is
almost certainly first-order. The nontrivial measure term enlarges the phase
diagram, allowing us to explore a region of the phase diagram that has been
dubbed the crinkled region. Although the collapsed and branched polymer phases
have been studied extensively in the literature, the crinkled region has not
received the same scrutiny. We find that the crinkled region is likely a part
of the collapsed phase with particularly large finite-size effects.
Intriguingly, the behavior of the spectral dimension in the crinkled region at
small volumes is similar to that of CDT, as first reported in arXiv:1104.5505,
but for sufficiently large volumes the crinkled region does not appear to have
4-dimensional semiclassical features. Thus, we find that the crinkled region of
the EDT formulation does not share the good features of the extended phase of
CDT, as we first suggested in arXiv:1104.5505. This agrees with the recent
results of arXiv:1307.2270, in which the authors used a somewhat different
discretization of EDT from the one presented here.Comment: 36 pages, 27 figures. Typos corrected, improved analysis of phase
transition, and clarifications added. Conclusions unchanged. Conforms with
version published in JHE
Topological fermion condensates from anomalies
We show that a class of fermion theory formulated on a compact, curved
manifold will generate a condensate whose magnitude is determined only by the
volume and Euler characteristic of the space. The construction requires that
the fermions be treated as K\"{a}hler-Dirac fields and the condensate arises
from an anomaly associated with a global symmetry which is subsequently
broken to a discrete subgroup. Remarkably the anomaly survives under
discretization of the space which allows us to compute the condensate on an
arbitrary triangulation. The results, being topological in character, should
hold in a wide range of gravitationally coupled fermion theories both classical
and quantumComment: 10 pages, 2 figures, 2 tables. minor corrections. Version published
in JHE
Lattice quantum gravity with scalar fields
We consider the four-dimensional Euclidean dynamical triangulations lattice
model of quantum gravity based on triangulations of . We couple it
minimally to a scalar field in the quenched approximation. Our results suggest
a multiplicative renormalization for the mass of the scalar field which is
consistent with the shift symmetry of the discretized lattice action. We
discuss the possibility of measuring the mass anomalous dimension and the
gravitational binding energy between two scalar test particles, where a
negative bound state energy would imply that this model has an attractive
gravitational force.Comment: 1+6 pages, proceedings for the 36th International Symposium on
Lattice Field Theory (22-28 July 2018). v2 -- Added one reference and fixed a
typo. Comments welcome
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