8,220 research outputs found
(2,0) Superconformal OPEs in D=6, Selection Rules and Non-renormalization Theorems
We analyse the OPE of any two 1/2 BPS operators of (2,0) SCFT by
constructing all possible three-point functions that they can form with
another, in general long operator. Such three-point functions are uniquely
determined by superconformal symmetry. Selection rules are derived, which allow
us to infer ``non-renormalization theorems'' for an abstract superconformal
field theory. The latter is supposedly related to the strong-coupling dynamics
of coincident M5 branes, dual, in the large- limit, to the bulk
M-theory compactified on AdSS. An interpretation of extremal and
next-to-extremal correlators in terms of exchange of operators with protected
conformal dimension is given.Comment: some details correcte
CRASH: a Radiative Transfer Scheme
We present a largely improved version of CRASH, a 3-D radiative transfer code
that treats the effects of ionizing radiation propagating through a given
inhomogeneous H/He cosmological density field, on the physical conditions of
the gas. The code, based on a Monte Carlo technique, self-consistently
calculates the time evolution of gas temperature and ionization fractions due
to an arbitrary number of point/extended sources and/or diffuse background
radiation with given spectra. In addition, the effects of diffuse ionizing
radiation following recombinations of ionized atoms have been included. After a
complete description of the numerical scheme, to demonstrate the performances,
accuracy, convergency and robustness of the code we present four different test
cases designed to investigate specific aspects of radiative transfer: (i) pure
hydrogen isothermal Stromgren sphere; (ii) realistic Stromgren spheres; (iii)
multiple overlapping point sources, and (iv) shadowing of background radiation
by an intervening optically thick layer. When possible, detailed quantitative
comparison of the results against either analytical solutions or 1-D standard
photoionization codes has been made showing a good level of agreement. For more
complicated tests the code yields physically plausible results, which could be
eventually checked only by comparison with other similar codes. Finally, we
briefly discuss future possible developments and cosmological applications of
the code.Comment: 17 pages, 14 figures, accepted for pubblication in MNRAS, high res
figures available at
http://www.arcetri.astro.it/science/cosmology/IGM/radtrans.htm
Inhomogeneous Reionization Regulated by Radiative and Stellar Feedbacks
We study the inhomogeneous reionization in a critical density CDM universe
due to stellar sources, including Population III objects. The spatial
distribution of the sources is obtained from high resolution numerical N-body
simulations. We calculate the source properties taking into account a
self-consistent treatment of both radiative (ie ionizing and H2
-photodissociating photons) and stellar (ie SN explosions) feedbacks regulated
by massive stars. This allows us to describe the topology of the ionized and
dissociated regions at various cosmic epochs and derive the evolution of H, He,
and H2 filling factors, soft UV background, cosmic star formation rate and the
final fate of ionizing objects. The main results are: (i) galaxies reionize the
IGM by z~10 (with some uncertainty related to the gas clumping factor), whereas
H2 is completely dissociated already by z~25; (ii) reionization is mostly due
to the relatively massive objects which collapse via H line cooling, while
objects whose formation relies on H2 cooling alone are insufficient to this
aim; (iii) the diffuse soft UV background is the major source of radiative
feedback effects for z<15; at higher z direct flux from neighboring objects
dominates; (iv) the match of the calculated cosmic star formation history with
the one observed at lower redshifts suggests that the conversion efficiency of
baryons into stars is ~1%; (v) we find that a very large population of dark
objects which failed to form stars is present by z~8. We discuss and compare
our results with similar previous studies.Comment: 34 pages, emulateapj.sty, LaTeX, 13 figures. MNRAS, submitte
Shortening of primary operators in N-extended SCFT_4 and harmonic-superspace analyticity
We present the analysis of all possible shortenings which occur for composite
gauge invariant conformal primary superfields in SU(2,2/N) invariant gauge
theories. These primaries have top-spin range N/2 \leq J_{max} < N with J_{max}
= J_1 + J_2, (J_1,J_2) being the SL(2,C) quantum numbers of the highest spin
component of the superfield. In Harmonic superspace, analytic and chiral
superfields give J_{max}= N/2 series while intermediate shortenings correspond
to fusion of chiral with analytic in N=2, or analytic with different analytic
structures in N=3,4. In the AdS/CFT language shortenings of UIR's correspond to
all possible BPS conditions on bulk states. An application of this analysis to
multitrace operators, corresponding to multiparticle supergravity states, is
spelled out.Comment: 44 pages, LaTeX; typos corrected, some references adde
Non-anticommutative chiral singlet deformation of N=(1,1) gauge theory
We study the SO(4)x SU(2) invariant Q-deformation of Euclidean N=(1,1) gauge
theories in the harmonic superspace formulation. This deformation preserves
chirality and Grassmann harmonic analyticity but breaks N=(1,1) to N=(1,0)
supersymmetry. The action of the deformed gauge theory is an integral over the
chiral superspace, and only the purely chiral part of the covariant superfield
strength contributes to it. We give the component form of the N=(1,0)
supersymmetric action for the gauge groups U(1) and U(n>1). In the U(1) and
U(2) cases, we find the explicit nonlinear field redefinition (Seiberg-Witten
map) relating the deformed N=(1,1) gauge multiplet to the undeformed one. This
map exists in the general U(n) case as well, and we use this fact to argue that
the deformed U(n) gauge theory can be nonlinearly reduced to a theory with the
gauge group SU(n).Comment: 1+25 pages; v2: corrected eqs.(2.7),(3.12),(4.31-33) and typos; v3:
corrected eqs.(3.29),(4.7),(A.5),(A.21), ref. added, published versio
Partial Spontaneous Breaking of Global Supersymmetry
We review in detail the recently discovered phenomenon of partial spontaneous
breaking of supersymmetry in the case of a N=2 pure gauge U(1) theory, and
recall how the standard lore no-go theorem is evaded. We discuss the extension
of this mechanism to theories with charged matter, and surprisingly find that
the gauging forbids the existence of a magnetic Fayet-Iliopoulos term.Comment: Contribution to the proceedings of the International Symposium
Ahrenshoop on the Theory of Elementary Particles, Buckow, Germany, August
27-31, 1996. LaTex2e, uses espcrc2.st
Initial mass function of intermediate mass black hole seeds
We study the Initial Mass Function (IMF) and host halo properties of
Intermediate Mass Black Holes (IMBH, 10^{4-6} Msun) formed inside metal-free,
UV illuminated atomic cooling haloes (virial temperature T_vir > 10^4 K) either
via the direct collapse of the gas or via an intermediate Super Massive Star
(SMS) stage. We achieve this goal in three steps: (a) we derive the gas
accretion rate for a proto-SMS to undergo General Relativity instability and
produce a direct collapse black hole (DCBH) or to enter the ZAMS and later
collapse into a IMBH; (b) we use merger-tree simulations to select atomic
cooling halos in which either a DCBH or SMS can form and grow, accounting for
metal enrichment and major mergers that halt the growth of the proto-SMS by gas
fragmentation. We derive the properties of the host halos and the mass
distribution of black holes at this stage, and dub it the "Birth Mass
Function"; (c) we follow the further growth of the DCBH due to accretion of
leftover gas in the parent halo and compute the final IMBH mass.We consider two
extreme cases in which minihalos (T_vir < 10^4 K) can (fertile) or cannot
(sterile) form stars and pollute their gas leading to a different IMBH IMF. In
the (fiducial) fertile case the IMF is bimodal extending over a broad range of
masses, M= (0.5-20)x10^5 Msun, and the DCBH accretion phase lasts from 10 to
100 Myr. If minihalos are sterile, the IMF spans the narrower mass range M=
(1-2.8)x10^6 Msun, and the DCBH accretion phase is more extended (70-120 Myr).
We conclude that a good seeding prescription is to populate halos (a) of mass
7.5 < log (M_h/Msun) < 8, (b) in the redshift range 8 < z < 17, (c) with IMBH
in the mass range 4.75 < log (M_BH/Msun) < 6.25.Comment: MNRAS, in press. Comments welcom
On the [CII]-SFR relation in high redshift galaxies
After two ALMA observing cycles, only a handful of [CII]
emission line searches in z>6 galaxies have reported a positive detection,
questioning the applicability of the local [CII]-SFR relation to high-z
systems. To investigate this issue we use the Vallini et al. 2013 (V13) model,
based on high-resolution, radiative transfer cosmological simulations to
predict the [CII] emission from the interstellar medium of a z~7 (halo mass
) galaxy. We improve the V13 model by including
(a) a physically-motivated metallicity (Z) distribution of the gas, (b) the
contribution of Photo-Dissociation Regions (PDRs), (c) the effects of Cosmic
Microwave Background on the [CII] line luminosity. We study the relative
contribution of diffuse neutral gas to the total [CII] emission () for different SFR and Z values. We find that the [CII]
emission arises predominantly from PDRs: regardless of the galaxy properties,
% since, at these early epochs, the CMB temperature
approaches the spin temperature of the [CII] transition in the cold neutral
medium ( K). Our model predicts a high-z
[CII]-SFR relation consistent with observations of local dwarf galaxies
(). The [CII] deficit suggested by actual data
( in BDF3299 at z~7.1) if confirmed by deeper
ALMA observations, can be ascribed to negative stellar feedback disrupting
molecular clouds around star formation sites. The deviation from the local
[CII]-SFR would then imply a modified Kennicutt-Schmidt relation in z>6
galaxies. Alternatively/in addition, the deficit might be explained by low gas
metallicities ().Comment: 9 pages, 6 figures, replaced with the version accepted for
pubblication in Ap
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