717 research outputs found
Quantization of Diffeomorphism-Invariant Theories with Fermions
We extend ideas developed for the loop representation of quantum gravity to
diffeomorphism-invariant gauge theories coupled to fermions. Let P -> Sigma be
a principal G-bundle over space and let F be a vector bundle associated to P
whose fiber is a sum of continuous unitary irreducible representations of the
compact connected gauge group G, each representation appearing together with
its dual. We consider theories whose classical configuration space is A x F,
where A is the space of connections on P and F is the space of sections of F,
regarded as a collection of Grassmann-valued fermionic fields. We construct the
`quantum configuration space a x f as a completion of A x F. Using this we
construct a Hilbert space L^2(a x f) for the quantum theory on which all
automorphisms of P act as unitary operators, and determine an explicit `spin
network basis' of the subspace L^2((a x f)/G) consisting of gauge-invariant
states. We represent observables constructed from holonomies of the connection
along paths together with fermionic fields and their conjugate momenta as
operators on L^2((a x f)/G). We also construct a Hilbert space H_diff of
diffeomorphism-invariant states using the group averaging procedure of
Ashtekar, Lewandowski, Marolf, Mourao and Thiemann.Comment: 28 pages, latex, 7 ps-files (included) are needed to process the
source fil
Muon g-2 through a flavor structure on soft SUSY terms
In this work we analyze the possibility to explain the muon anomalous
magnetic moment discrepancy within theory and experiment through lepton flavor
violation processes. We propose a flavor extended MSSM by considering a
hierarchical family structure for the trilinear scalar Soft-Supersymmetric
terms of the Lagranagian, present at the SUSY breaking scale. We obtain
analytical results for the rotation mass matrix, with the consequence of having
non-universal slepton masses and the possibility of leptonic flavour mixing.
The one-loop supersymmetric contributions to the leptonic flavour violating
process are calculated in the physical basis, with slepton
flavour mixed states, instead of using the well known Mass Insertion Method. We
present the regions in parameter space where the muon g-2 problem is either
entirely solved or partially reduced through the contribution of these flavor
violating processes.Comment: 21 pages, 7 figures. Changes on version 3: In order to obtain the
complete result for muon g-2 in the limit of non-flavor violation we added
the terms given in the appendix. We redid the graphics and numerical analysis
including these changes. We also corrected some typos and changed the order
of figure
Does cash for school influence young women's behavior in the longer term ? evidence from Pakistan
The Punjab Female School Stipend Program, a female-targeted conditional cash transfer program in Pakistan, was implemented in response to gender gaps in education. An early evaluation of the program shows that the enrollment of eligible girls in middle school increased in the short term by nearly 9 percentage points. This paper uses regression discontinuity and difference-in-difference analyses to show that five years into the program implementation positive impacts do persist. Beneficiary adolescent girls are more likely to progress through and complete middle school and work less. There is suggestive evidence that participating girls delay their marriage and have fewer births by the time they are 19 years old. Girls who are exposed to the program later, and who are eligible for the benefits given in high school, increase their rates of matriculating into and completing high school. The persistence of impacts can potentially translate into gains in future productivity, consumption, inter-generational human capital accumulation and desired fertility. Lastly, there is no evidence that the program has negative spillover effects on educational outcomes of male siblings.Education For All,Primary Education,Tertiary Education,Gender and Education,Disability
An Invitation to Higher Gauge Theory
In this easy introduction to higher gauge theory, we describe parallel
transport for particles and strings in terms of 2-connections on 2-bundles.
Just as ordinary gauge theory involves a gauge group, this generalization
involves a gauge '2-group'. We focus on 6 examples. First, every abelian Lie
group gives a Lie 2-group; the case of U(1) yields the theory of U(1) gerbes,
which play an important role in string theory and multisymplectic geometry.
Second, every group representation gives a Lie 2-group; the representation of
the Lorentz group on 4d Minkowski spacetime gives the Poincar\'e 2-group, which
leads to a spin foam model for Minkowski spacetime. Third, taking the adjoint
representation of any Lie group on its own Lie algebra gives a 'tangent
2-group', which serves as a gauge 2-group in 4d BF theory, which has
topological gravity as a special case. Fourth, every Lie group has an 'inner
automorphism 2-group', which serves as the gauge group in 4d BF theory with
cosmological constant term. Fifth, every Lie group has an 'automorphism
2-group', which plays an important role in the theory of nonabelian gerbes. And
sixth, every compact simple Lie group gives a 'string 2-group'. We also touch
upon higher structures such as the 'gravity 3-group' and the Lie 3-superalgebra
that governs 11-dimensional supergravity.Comment: 60 pages, based on lectures at the 2nd School and Workshop on Quantum
Gravity and Quantum Geometry at the 2009 Corfu Summer Institut
A pilot search for mm-wavelength recombination lines from emerging ionized winds in pre-planetary nebulae candidates
We report the results from a pilot search for radio recombination line (RRL)
emission at millimeter wavelengths in a small sample of pre-planetary nebulae
(pPNe) and young PNe (yPNe) with emerging central ionized regions. Observations
of the H30\alpha, H31a, H39a, H41a, H48b, H49b, H51b, and H55g lines at 1 and
3mm have been performed with the IRAM 30 m radio telescope. These lines are
excellent probes of the dense inner (<~150 au) and heavily obscured regions of
these objects, where the yet unknown agents for PN-shaping originate. We
detected mm-RRLs in three objects: CRL 618, MWC 922, and M 2-9. For CRL 618,
the only pPN with previous published detections of H41a, H35a, and H30a
emission, we find significant changes in the line profiles indicating that
current observations are probing regions of the ionized wind with larger
expansion velocities and mass-loss rate than ~29 years ago. In the case of MWC
922, we observe a drastic transition from single-peaked profiles at 3mm to
double-peaked profiles at 1mm, which is consistent with maser amplification of
the highest frequency lines; the observed line profiles are compatible with
rotation and expansion of the ionized gas, probably arranged in a disk+wind
system around a ~5-10 Msun central mass. In M 2-9, the mm-RRL emission appears
to be tracing a recent mass outburst by one of the stars of the central binary
system. We present the results from non-LTE line and continuum radiative
transfer models, which enables us to constrain the structure, kinematics, and
physical conditions (electron temperature and density) of the ionized cores of
our sample. (abridged). We deduce mass-loss rates of ~1e-6-1e-7 Msun/yr, which
are significantly higher than the values adopted by stellar evolution models
currently in use and would result in a transition from the asymptotic giant
branch to the PN phase faster than hitherto assumed.Comment: Accepted by Astronomy and Astrophysics. 28 pages, including figure
Asymptotics of Relativistic Spin Networks
The stationary phase technique is used to calculate asymptotic formulae for
SO(4) Relativistic Spin Networks. For the tetrahedral spin network this gives
the square of the Ponzano-Regge asymptotic formula for the SU(2) 6j symbol. For
the 4-simplex (10j-symbol) the asymptotic formula is compared with numerical
calculations of the Spin Network evaluation. Finally we discuss the asymptotics
of the SO(3,1) 10j-symbol.Comment: 31 pages, latex. v3: minor clarification
Group field theory and simplicial gravity path integrals: A model for Holst-Plebanski gravity
In a recent work, a dual formulation of group field theories as
non-commutative quantum field theories has been proposed, providing an exact
duality between spin foam models and non-commutative simplicial path integrals
for constrained BF theories. In light of this new framework, we define a model
for 4d gravity which includes the Immirzi parameter gamma. It reproduces the
Barrett-Crane amplitudes when gamma goes to infinity, but differs from existing
models otherwise; in particular it does not require any rationality condition
for gamma. We formulate the amplitudes both as BF simplicial path integrals
with explicit non-commutative B variables, and in spin foam form in terms of
Wigner 15j-symbols. Finally, we briefly discuss the correlation between
neighboring simplices, often argued to be a problematic feature, for example,
in the Barrett-Crane model.Comment: 26 pages, 1 figur
Spin Foam Models of Riemannian Quantum Gravity
Using numerical calculations, we compare three versions of the Barrett-Crane
model of 4-dimensional Riemannian quantum gravity. In the version with face and
edge amplitudes as described by De Pietri, Freidel, Krasnov, and Rovelli, we
show the partition function diverges very rapidly for many triangulated
4-manifolds. In the version with modified face and edge amplitudes due to Perez
and Rovelli, we show the partition function converges so rapidly that the sum
is dominated by spin foams where all the spins labelling faces are zero except
for small, widely separated islands of higher spin. We also describe a new
version which appears to have a convergent partition function without drastic
spin-zero dominance. Finally, after a general discussion of how to extract
physics from spin foam models, we discuss the implications of convergence or
divergence of the partition function for other aspects of a spin foam model.Comment: 23 pages LaTeX; this version to appear in Classical and Quantum
Gravit
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