311 research outputs found
Hamilton-Jacobi Method and Gravitation
Studying the behaviour of a quantum field in a classical, curved, spacetime
is an extraordinary task which nobody is able to take on at present time.
Independently by the fact that such problem is not likely to be solved soon,
still we possess the instruments to perform exact predictions in special,
highly symmetric, conditions. Aim of the present contribution is to show how it
is possible to extract quantitative information about a variety of physical
phenomena in very general situations by virtue of the so-called Hamilton-Jacobi
method. In particular, we shall prove the agreement of such semi-classical
method with exact results of quantum field theoretic calculations.Comment: To appear in the proceedings of "Cosmology, the Quantum Vacuum, and
Zeta Functions": A workshop with a celebration of Emilio Elizalde's Sixtieth
birthday, Bellaterra, Barcelona, Spain, 8-10 Mar 201
Pulsating Strings in Lunin-Maldacena Backgrounds
We consider pulsating strings in Lunin-Maldacena backgrounds, specifically in
deformed Minkowski spacetime and deformed AdS_5xS^5. We find the relation
between the energy and the oscillation number of the pulsating string when the
deformation is small. Since the oscillation number is an adiabatic invariant it
can be used to explore the regime of highly excited string states. We then
quantize the string and look for such a sector. For the deformed Minkowski
background we find a precise match with the classical results if the
oscillation number is quantized as an even number. For the deformed AdS_5xS^5
we find a contribution which depends on the deformation parameter.Comment: 16 pages, 2 figures, typos fixe
Regularization and Anomalies in Gauge Theory
Some of the basic issues related to the regularization and anomalies in gauge
theory are reviewed, with particular emphasis on the recent development in
lattice gauge theory. The generalized Pauli-Villars regularization is discussed
from a view point of the covariant regularization of currents, and the
construction of a regularized effective action in terms of covariant currents
is compared with the lattice formulation of chiral Abelian theory.Comment: 14 pages. Talk given at NATO Advanced Research Workshop ``Lattice
Fermions and Structure of the Vacuum'', October 5-9, 1999, at Dubna, Russia
(To be published in the Proceedings
The dual string sigma-model of the SU_q(3) sector
In four-dimensional N=4 super Yang-Mills (SYM) the SU(3) sub-sector spanned
by purely holomorphic fields is isomorphic to the corresponding mixed one
spanned by both holomorphic and antiholomorphic fields. This is no longer the
case when one considers the marginally deformed N=4 SYM. The mixed SU(3) sector
marginally deformed by a complex parameter beta, i.e. SU_q(3) with q=e^{2
i\pi\beta}, has been shown to be integrable at one-loop hep-th/0703150, while
it is not the case for the corresponding purely holomorphic one. Moreover, the
marginally deformed N=4 SYM also has a gravity dual constructed by Lunin and
Maldacena in hep-th/0502086. However, the mixed SU_q(3) sector has not been
studied from the supergravity point of view. Hence in this note, for the case
of purely imaginary marginal -deformations, we compute the superstring
SU_q(3) \sigma-model in the fast spinning string limit and show that, for
rational spinning strings, it reproduces the energy computed via Bethe
equations.Comment: 20 page
Classical integrability in the BTZ black hole
Using the fact the BTZ black hole is a quotient of AdS_3 we show that
classical string propagation in the BTZ background is integrable. We construct
the flat connection and its monodromy matrix which generates the non-local
charges. From examining the general behaviour of the eigen values of the
monodromy matrix we determine the set of integral equations which constrain
them. These equations imply that each classical solution is characterized by a
density function in the complex plane. For classical solutions which correspond
to geodesics and winding strings we solve for the eigen values of the monodromy
matrix explicitly and show that geodesics correspond to zero density in the
complex plane. We solve the integral equations for BMN and magnon like
solutions and obtain their dispersion relation. Finally we show that the set of
integral equations which constrain the eigen values of the monodromy matrix can
be identified with the continuum limit of the Bethe equations of a twisted
SL(2, R) spin chain at one loop.Comment: 45 pages, Reference added, typos corrected, discussion on geodesics
improved to include all geodesic
Observation of second-harmonic generation induced by pure spin currents
Extensive efforts are currently being devoted to developing a new electronic
technology, called spintronics, where the spin of electrons is explored to
carry information. [1,2] Several techniques have been developed to generate
pure spin currents in many materials and structures. [3-10] However, there is
still no method available that can be used to directly detect pure spin
currents, which carry no net charge current and no net magnetization.
Currently, studies of pure spin currents rely on measuring the induced spin
accumulation with optical techniques [5, 11-13] or spin-valve configurations.
[14-17] However, the spin accumulation does not directly reflect the spatial
distribution or temporal dynamics of the pure spin current, and therefore
cannot monitor the pure spin current in a real-time and real-space fashion.
This imposes severe constraints on research in this field. Here we demonstrate
a second-order nonlinear optical effect of the pure spin current. We show that
such a nonlinear optical effect, which has never been explored before, can be
used for the non-invasive, non-destructive, and real-time imaging of pure spin
currents. Since this detection scheme does not rely on optical resonances, it
can be generally applied in a wide range of materials with different electronic
bandstructures. Furthermore, the control of nonlinear optical properties of
materials with pure spin currents may have potential applications in photonics
integrated with spintronics.Comment: 19 pages, 3 figures, supplementary discussion adde
Deformation of Codimension-2 Surface and Horizon Thermodynamics
The deformation equation of a spacelike submanifold with an arbitrary
codimension is given by a general construction without using local frames. In
the case of codimension-1, this equation reduces to the evolution equation of
the extrinsic curvature of a spacelike hypersurface. In the more interesting
case of codimension-2, after selecting a local null frame, this deformation
equation reduces to the well known (cross) focusing equations. We show how the
thermodynamics of trapping horizons is related to these deformation equations
in two different formalisms: with and without introducing quasilocal energy. In
the formalism with the quasilocal energy, the Hawking mass in four dimension is
generalized to higher dimension, and it is found that the deformation of this
energy inside a marginal surface can be also decomposed into the contributions
from matter fields and gravitational radiation as in the four dimension. In the
formalism without the quasilocal energy, we generalize the definition of slowly
evolving future outer trapping horizons proposed by Booth to past trapping
horizons. The dynamics of the trapping horizons in FLRW universe is given as an
example. Especially, the slowly evolving past trapping horizon in the FLRW
universe has close relation to the scenario of slow-roll inflation. Up to the
second order of the slowly evolving parameter in this generalization, the
temperature (surface gravity) associated with the slowly evolving trapping
horizon in the FLRW universe is essentially the same as the one defined by
using the quasilocal energy.Comment: Latex, 61 pages, no figures; v2, type errors corrected; v3,
references and comments are added, English is improved, to appear in JHE
Spinning strings and integrable spin chains in the AdS/CFT correspondence
In this introductory review we discuss dynamical tests of the AdS_5 x S^5
string/N=4 super Yang-Mills duality. After a brief introduction to AdS/CFT we
argue that semiclassical string energies yield information on the quantum
spectrum of the string in the limit of large angular momenta on the S^5. The
energies of the folded and circular spinning string solutions rotating on a S^3
within the S^5 are derived, which yield all loop predictions for the dual gauge
theory scaling dimensions. These follow from the eigenvalues of the dilatation
operator of N=4 super Yang-Mills in a minimal SU(2) subsector and we display
its reformulation in terms of a Heisenberg s=1/2 spin chain along with the
coordinate Bethe ansatz for its explicit diagonalization. In order to make
contact to the spinning string energies we then study the thermodynamic limit
of the one-loop gauge theory Bethe equations and demonstrate the matching with
the folded and closed string result at this loop order. Finally the known gauge
theory results at higher-loop orders are reviewed and the associated long-range
spin chain Bethe ansatz is introduced, leading to an asymptotic all-loop
conjecture for the gauge theory Bethe equations. This uncovers discrepancies at
the three-loop order between gauge theory scaling dimensions and string theory
energies and the implications of this are discussed. Along the way we comment
on further developments and generalizations of the subject and point to the
relevant literature.Comment: 40 pages, invited contribution to Living Reviews in Relativity. v2:
improvements in the text and references adde
Ballistic Spin Resonance
The phenomenon of spin resonance has had far reaching influence since its
discovery nearly 70 years ago. Electron spin resonance (ESR) driven by high
frequency magnetic fields has informed our understanding of quantum mechanics,
and finds application in fields as diverse as medicine and quantum information.
Spin resonance induced by high frequency electric fields, known as electric
dipole spin resonance (EDSR), has also been demonstrated recently. EDSR is
mediated by spin-orbit interaction (SOI), which couples the spin degree of
freedom and the momentum vector. Here, we report the observation of a novel
spin resonance due to SOI that does not require external driving fields.
Ballistic spin resonance (BSR) is driven by an internal spin-orbit field that
acts upon electrons bouncing at gigaHertz frequencies in narrow channels of
ultra-clean two-dimensional electron gas (2DEG). BSR is manifested in
electrical measurements of pure spin currents as a strong suppression of spin
relaxation length when the motion of electrons is in resonance with spin
precession. These findings point the way to gate-tunable coherent spin
rotations in ballistic nanostructures without external a.c. fields.Comment: 24 pages, including supplementary material
Twisted Bethe equations from a twisted S-matrix
All-loop asymptotic Bethe equations for a 3-parameter deformation of
AdS5/CFT4 have been proposed by Beisert and Roiban. We propose a Drinfeld twist
of the AdS5/CFT4 S-matrix, together with c-number diagonal twists of the
boundary conditions, from which we derive these Bethe equations. Although the
undeformed S-matrix factorizes into a product of two su(2|2) factors, the
deformed S-matrix cannot be so factored. Diagonalization of the corresponding
transfer matrix requires a generalization of the conventional algebraic Bethe
ansatz approach, which we first illustrate for the simpler case of the twisted
su(2) principal chiral model. We also demonstrate that the same twisted Bethe
equations can alternatively be derived using instead untwisted S-matrices and
boundary conditions with operatorial twists.Comment: 42 pages; v2: a new appendix on sl(2) grading, 2 additional
references, and some minor changes; v3: improved Appendix D, additional
references, and further minor changes, to appear in JHE
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