16 research outputs found
Ultraviolet asymptotics for quasiperiodic AdS_4 perturbations
Spherically symmetric perturbations in AdS-scalar field systems of small
amplitude epsilon approximately periodic on time scales of order 1/epsilon^2
(in the sense that no significant transfer of energy between the AdS normal
modes occurs) have played an important role in considerations of AdS stability.
They are seen as anchors of stability islands where collapse of small
perturbations to black holes does not occur. (This collapse, if it happens,
typically develops on time scales of the order 1/epsilon^2.) We construct an
analytic treatment of the frequency spectra of such quasiperiodic
perturbations, paying special attention to the large frequency asymptotics. For
the case of a self-interacting phi^4 scalar field in a non-dynamical AdS
background, we arrive at a fairly complete analytic picture involving
quasiperiodic spectra with an exponential suppression modulated by a power law
at large mode numbers. For the case of dynamical gravity, the structure of the
large frequency asymptotics is more complicated. We give analytic explanations
for the general qualitative features of quasiperiodic solutions localized
around a single mode, in close parallel to our discussion of the probe scalar
field, and find numerical evidence for logarithmic modulations in the
gravitational quasiperiodic spectra existing on top of the formulas previously
reported in the literature.Comment: 18 pages; v3: minor improvements, published versio
Gravitational collapse and thermalization in the hard wall model
We study a simple example of holographic thermalization in a confining field
theory: the homogeneous injection of energy in the hard wall model. Working in
an amplitude expansion, we find black brane formation for sufficiently fast
energy injection and a scattering wave solution for sufficiently slow
injection. We comment on our expectations for more sophisticated holographic
QCD models.Comment: 33 pages, 5 figure
Yukawa couplings and masses of non-chiral states for the Standard Model on D6-branes on T6/Z6'
The perturbative leading order open string three-point couplings for the
Standard Model with hidden USp(6) on fractional D6-branes on T6/Z6' from
arXiv:0806.3039 [hep-th], arXiv:0910.0843 [hep-th] are computed. Physical
Yukawa couplings consisting of holomorphic Wilsonian superpotential terms times
a non-holomorphic prefactor involving the corresponding classical open string
Kaehler metrics are given, and mass terms for all non-chiral matter states are
derived. The lepton Yukawa interactions are at leading order flavour diagonal,
while the quark sector displays a more intricate pattern of mixings. While N=2
supersymmetric sectors acquire masses via only two D6-brane displacements -
which also provide the hierarchies between up- and down-type Yukawas within one
quark or lepton generation -, the remaining vector-like states receive masses
via perturbative three-point couplings to some Standard Model singlet fields
with vevs along flat directions. Couplings to the hidden sector and messengers
for supersymmetry breaking are briefly discussed.Comment: 52 pages (including 8p. appendix); 5 figures; 14 tables; v2:
discussion in section 4.1.3 extended, footnote 5 added, typos corrected,
accepted by JHE
Holographic Hall conductivities from dyonic backgrounds
We develop a general framework for computing the holographic 2-point
functions and the corresponding conductivities in asymptotically locally AdS
backgrounds with an electric charge density, a constant magentic field, and
possibly non-trivial scalar profiles, for a broad class of
Einstein-Maxwell-Axion-Dilaton theories, including certain Chern-Simons terms.
Holographic renormalization is carried out for any theory in this class and the
computation of the renormalized AC conductivities at zero spatial momentum is
reduced to solving a single decoupled first order Riccati equation. Moreover,
we develop a first order fake supergravity formulalism for dyonic
renormalization group flows in four dimensions, allowing us to construct
analytically infinite families of such backgrounds by specifying a
superpotential at will. These RG flows interpolate between AdS in the UV
and a hyperscaling violating Lifshitz geometry in the IR with exponents
and . For the spectrum of fluctuations is gapped and
discrete. Our hope and intention is that this analysis can serve as a manual
for computing the holographic 1- and 2-point functions and the corresponding
transport coefficients in any dyonic background, both in the context of AdS/CMT
and AdS/QCD