9,924 research outputs found
The ability of fifth grade children to discriminate between fact and opinion statement
Thesis (Ed.M.)--Boston Universit
Dualities Compositeness and Spacetime Structure of 4d Extreme Stringy Black Holes
We study the BPS black hole solutions of the (truncated) action for heterotic
string theory compactified on a six-torus. The O(3,Z) duality symmetry of the
theory, together with the bound state interpretation of extreme black holes, is
used to generate the whole spectrum of the solutions. The corresponding
spacetime structures, written in terms of the string metric, are analyzed in
detail. In particular, we show that only the elementary solutions present naked
singularities. The bound states have either null singularities (electric
solutions) or are regular (magnetic or dyonic solutions) with near-horizon
geometries given by the product of two 2d spaces of constant curvature. The
behavior of some of these solutions as supersymmetric attractors is discussed.
We also show that our approach is very useful to understand some of the
puzzling features of charged black hole solutions in string theory.Comment: 17 pages, LaTex, no figure
Supergravity Predictions on Conformal Field Theories
We give an update on recent results about the matching between CFT operators
and KK states in the AdS/CFT correspondence, and add some new comments on the
realization of the baryonic symmetries from the supergravity point of view.Comment: 8 pages, uses JHEP.cls, Contribution to the proceedings of the TMR
Conference on Quantum Aspects of Gauge Theories, Supersymmetry and
Unification, Paris, 1-7 September 199
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
Black Hole Superpartners and Fixed Scalars
Some bosonic solutions of supergravities admit Killing spinors of unbroken
supersymmetry. The anti-Killing spinors of broken supersymmetry can be used to
generate the superpartners of stringy black holes. This has a consequent
feedback on the metric and the graviphoton. We have found however that the
fixed scalars for the black hole superpartners remain the same as for the
original black holes. Possible phenomenological implications of this result are
discussed.Comment: 6 pages, Late
Looking at cosmic near-infrared background radiation anisotropies
The cosmic infrared background (CIB) contains emissions accumulated over the
entire history of the Universe, including from objects inaccessible to
individual telescopic studies. The near-IR (~1-10 mic) part of the CIB, and its
fluctuations, reflects emissions from nucleosynthetic sources and
gravitationally accreting black holes (BHs). If known galaxies are removed to
sufficient depths the source-subtracted CIB fluctuations at near-IR can reveal
sources present in the first-stars-era and possibly new stellar populations at
more recent times. This review discusses the recent progress in this newly
emerging field which identified, with new data and methodology, significant
source-subtracted CIB fluctuations substantially in excess of what can be
produced by remaining known galaxies. The CIB fluctuations further appear
coherent with unresolved cosmic X-ray background (CXB) indicating a very high
fraction of BHs among the new sources producing the CIB fluctuations. These
observations have led to intensive theoretical efforts to explain the
measurements and their properties. While current experimental configurations
have limitations in decisively probing these theories, their potentially
remarkable implications will be tested in the upcoming CIB measurements with
the ESA's Euclid dark energy mission. We describe the goals and methodologies
of LIBRAE (Looking at Infrared Background Radiation with Euclid), a
NASA-selected project for CIB science with Euclid, which has the potential for
transforming the field into a new area of precision cosmology.Comment: Reviews of Modern Physics, to appea
On the Stability of Non-Supersymmetric Quantum Attractors in String Theory
We study four dimensional non-supersymmetric attractors in type IIA string
theory in the presence of sub-leading corrections to the prepotential. For a
given Calabi-Yau manifold, the D0-D4 system admits an attractor point in the
moduli space which is uniquely specified by the black hole charges. The
perturbative corrections to the prepotential do not change the number of
massless directions in the black hole effective potential. We further study
non-supersymmetric D0-D6 black holes in the presence of sub-leading
corrections. In this case the space of attractor points define a hypersurface
in the moduli space.Comment: References Added, Typos Corrected, Appendix A.2 Reordere
Matrix Norms, BPS Bounds and Marginal Stability in N=8 Supergravity
We study the conditions of marginal stability for two-center extremal black
holes in N-extended supergravity in four dimensions, with particular emphasis
on the N=8 case. This is achieved by exploiting triangle inequalities satisfied
by matrix norms. Using different norms and relative bounds among them, we
establish the existence of marginal stability and split attractor flows both
for BPS and some non-BPS solutions. Our results are in agreement with previous
analysis based on explicit construction of multi-center solutions.Comment: 1+15 pages; v2: some new formulas added and misprints corrected; v3:
typos fixed, various refinements, Sec. 2.4 rewritten; to appear on JHE
List Distinguishing Parameters of Trees
A coloring of the vertices of a graph G is said to be distinguishing}
provided no nontrivial automorphism of G preserves all of the vertex colors.
The distinguishing number of G, D(G), is the minimum number of colors in a
distinguishing coloring of G. The distinguishing chromatic number of G,
chi_D(G), is the minimum number of colors in a distinguishing coloring of G
that is also a proper coloring.
Recently the notion of a distinguishing coloring was extended to that of a
list distinguishing coloring. Given an assignment L= {L(v) : v in V(G)} of
lists of available colors to the vertices of G, we say that G is (properly)
L-distinguishable if there is a (proper) distinguishing coloring f of G such
that f(v) is in L(v) for all v. The list distinguishing number of G, D_l(G), is
the minimum integer k such that G is L-distinguishable for any list assignment
L with |L(v)| = k for all v. Similarly, the list distinguishing chromatic
number of G, denoted chi_{D_l}(G) is the minimum integer k such that G is
properly L-distinguishable for any list assignment L with |L(v)| = k for all v.
In this paper, we study these distinguishing parameters for trees, and in
particular extend an enumerative technique of Cheng to show that for any tree
T, D_l(T) = D(T), chi_D(T)=chi_{D_l}(T), and chi_D(T) <= D(T) + 1.Comment: 10 page
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