124 research outputs found
On the worldsheet theory of the type IIA AdS(4) x CP(3) superstring
We perform a detailed study of the type IIA superstring in AdS(4) x CP(3).
After introducing suitable bosonic light-cone and fermionic kappa worldsheet
gauges we derive the pure boson and fermion SU(2|2) x U(1) covariant light-cone
Hamiltonian up to quartic order in fields.
As a first application of our derivation we calculate energy shifts for
string configurations in a closed fermionic subsector and successfully match
these with a set of light-cone Bethe equations. We then turn to investigate the
mismatch between the degrees of freedom of scattering states and oscillatory
string modes. Since only light string modes appear as fundamental Bethe roots
in the scattering theory, the physical role of the remaining massive
oscillators is rather unclear. By continuing a line of research initiated by
Zarembo, we shed light on this question by calculating quantum corrections for
the propagators of the bosonic massive fields. We show that, once loop
corrections are incorporated, the massive coordinates dissolve in a continuum
state of two light particles.Comment: 40 pages, 2 figures. v3: Minor clarifications made and reference list
updated. Published version
Chiral Extrapolation of the Strangeness Changing K pi Form Factor
We perform a chiral extrapolation of lattice data on the scalar K pi form
factor and the ratio of the kaon and pion decay constants within Chiral
Perturbation Theory to two loops. We determine the value of the scalar form
factor at zero momentum transfer, at the Callan-Treiman point and at its soft
kaon analog as well as its slope. Results are in good agreement with their
determination from experiment using the standard couplings of quarks to the W
boson. The slope is however rather large. A study of the convergence of the
chiral expansion is also performed.Comment: few minor change
Strings in AdS_4 x CP^3: finite size spectrum vs. Bethe Ansatz
We compute the first curvature corrections to the spectrum of light-cone
gauge type IIA string theory that arise in the expansion of about a plane-wave limit. The resulting spectrum is shown to
match precisely, both in magnitude and degeneration that of the corresponding
solutions of the all-loop Gromov--Vieira Bethe Ansatz. The one-loop dispersion
relation correction is calculated for all the single oscillator states of the
theory, with the level matching condition lifted. It is shown to have all
logarithmic divergences cancelled and to leave only a finite exponentially
suppressed contribution, as shown earlier for light bosons. We argue that there
is no ambiguity in the choice of the regularization for the self-energy sum,
since the regularization applied is the only one preserving unitarity.
Interaction matrices in the full degenerate two-oscillator sector are
calculated and the spectrum of all two light magnon oscillators is completely
determined. The same finite-size corrections, at the order 1/J, where is
the length of the chain, in the two-magnon sector are calculated from the all
loop Bethe Ansatz. The corrections obtained by the two completely different
methods coincide up to the fourth order in . We
conjecture that the equivalence extends to all orders in and to
higher orders in 1/J.Comment: 32 pages. Published version; journal reference adde
Classical integrability and quantum aspects of the AdS(3) x S(3) x S(3) x S(1) superstring
In this paper we continue the investigation of aspects of integrability of
the type IIA AdS(3) x S(3) x S(3) x S(1) and AdS(3) x S(3) x T(4) superstrings.
By constructing a one parameter family of flat connections we prove that the
Green-Schwarz string is classically integrable, at least to quadratic order in
fermions, without fixing the kappa-symmetry. We then compare the quantum
dispersion relation, fixed by integrability up to an unknown interpolating
function h(lambda), to explicit one-loop calculations on the string worldsheet.
For AdS(3) x S(3) x S(3) x S(1) the spectrum contains heavy, as well as light
and massless modes, and we find that the one-loop contribution differs
depending on how we treat these modes showing that similar regularization
ambiguities as appeared in AdS(4)/CFT(3) occur also here.Comment: 29 pages; v2: updated references and acknowledgmen
Unitarity and the Holographic S-Matrix
The bulk S-Matrix can be given a non-perturbative definition in terms of the
flat space limit of AdS/CFT. We show that the unitarity of the S-Matrix, ie the
optical theorem, can be derived by studying the behavior of the OPE and the
conformal block decomposition in the flat space limit. When applied to
perturbation theory in AdS, this gives a holographic derivation of the cutting
rules for Feynman diagrams.
To demonstrate these facts we introduce some new techniques for the analysis
of conformal field theories. Chief among these is a method for conglomerating
local primary operators to extract the contribution of an individual primary in
their OPE. This provides a method for isolating the contribution of specific
conformal blocks which we use to prove an important relation between certain
conformal block coefficients and anomalous dimensions. These techniques make
essential use of the simplifications that occur when CFT correlators are
expressed in terms of a Mellin amplitude.Comment: 33+12 pages, 6 figures; v2: typos corrected, some clarifications
adde
Charged-Higgs phenomenology in the Aligned two-Higgs-doublet model
The alignment in flavour space of the Yukawa matrices of a general
two-Higgs-doublet model results in the absence of tree-level flavour-changing
neutral currents. In addition to the usual fermion masses and mixings, the
aligned Yukawa structure only contains three complex parameters, which are
potential new sources of CP violation. For particular values of these three
parameters all known specific implementations of the model based on discrete
Z_2 symmetries are recovered. One of the most distinctive features of the
two-Higgs-doublet model is the presence of a charged scalar. In this work, we
discuss its main phenomenological consequences in flavour-changing processes at
low energies and derive the corresponding constraints on the parameters of the
aligned two-Higgs-doublet model.Comment: 46 pages, 19 figures. Version accepted for publication in JHEP.
References added. Discussion slightly extended. Conclusions unchange
Viral Load, Clinical Disease Severity and Cellular Immune Responses in Primary Varicella Zoster Virus Infection in Sri Lanka
BACKGROUND: In Sri Lanka, varicella zoster virus (VZV) is typically acquired during adulthood with significant associated disease morbidity and mortality. T cells are believed to be important in the control of VZV replication and in the prevention of reactivation. The relationship between viral load, disease severity and cellular immune responses in primary VZV infection has not been well studied. METHODOLOGY: We used IFNgamma ELISpot assays and MHC class II tetramers based on VZV gE and IE63 epitopes, together with quantitative real time PCR assays to compare the frequency and phenotype of specific T cells with virological and clinical outcomes in 34 adult Sri Lankan individuals with primary VZV infection. PRINCIPAL FINDINGS: Viral loads were found to be significantly higher in patients with moderate to severe infection compared to those with mild infection (p<0.001) and were significantly higher in those over 25 years of age (P<0.01). A significant inverse correlation was seen between the viral loads and the ex vivo IFNgamma ELISpot responses of patients (P<0.001, r = -0.85). VZV-specific CD4+ T cells expressed markers of intermediate differentiation and activation. CONCLUSIONS: Overall, these data show that increased clinical severity in Sri Lankan adults with primary VZV infection associates with higher viral load and reduced viral specific T cell responses
The Role of Cytokines which Signal through the Common γ Chain Cytokine Receptor in the Reversal of HIV Specific CD4(+) and CD8(+) T Cell Anergy
BACKGROUND: HIV specific T cells are putatively anergic in vivo. IL-2, a member of a class of cytokines that binds to receptors containing the common gamma chain (γc) has been shown to reverse anergy. We examined the role of γc cytokines in reversing HIV specific T cell anergy. METHODS: PBMC from untreated HIV-infected individuals were briefly exposed to a panel of γc cytokines, and frequencies of gag specific T cells were enumerated by intracellular IFN-γ flow cytometry. RESULTS: Of the γc cytokines, brief exposure to IL-2, IL-15, or combined IL-15/IL-7 significantly enhanced (range 2–7 fold) the CD4(+) and CD8(+) T cell IFN-γ responses to HIV gag, with IL-15 giving the greatest enhancement. The effects of cytokines were not due to enhanced proliferation of pre-existing antigen specific cells, but were due to a combination of enhanced cytokine production from antigen specific T cells plus activation of non-epitope specific T cells. CONCLUSIONS: These observations support the notion that a significant number of HIV specific T cells are circulating in an anergic state. IL-2, IL-7 and particularly IL-15 as an immune modulator to reverse HIV-1 specific T cell anergy should be investigated, with the caveat that non-specific activation of T cells may also be induced
Near BMN dynamics of the AdS(3) x S(3) x S(3) x S(1) superstring
We investigate the type IIA AdS(3) x S(3) x M(4) superstring with M(4)=S(3) x
S(1) or M(4)=T(4). String theory in this background is interesting because of
AdS3/CFT2 and its newly discovered integrable structures. We derive the kappa
symmetry gauge-fixed Green-Schwarz string action to quadratic order in fermions
and quartic order in fields utilizing a near BMN expansion. As a first
consistency check of our results we show that the two point functions are
one-loop finite in dimensional regularization. We then perform a Hamiltonian
analysis where we compare the energy of string states with the predictions of a
set of conjectured Bethe equations. While we find perfect agreement for single
rank one sectors, we find that the product SU(2) x SU(2) sector does not match
unless the Bethe equations decouple completely. We then calculate 2 to 2
bosonic tree-level scattering processes on the string worldsheet and show that
the two-dimensional S-matrix is reflectionless. This might be important due to
the presence of massless worldsheet excitations which are generally not
described by the Bethe equations.Comment: 28 pages; v2: Fixed signs and eq. (B.1), results unchanged, one
reference added; v3: Matches published versio
Pure spinor superfields and Born-Infeld theory
We present a method for introducing and analysing higher-derivative
deformations of maximally supersymmetric field theories. Such terms are built
in the pure spinor superfield framework, using a set of operators representing
physical fields. The action for abelian Born-Infeld theory becomes polynomial
in this language, and contains only a four-point interaction in addition to the
free action. Simplifications also occur in the non-abelian case.Comment: 23 pp., plain te
- …