236 research outputs found
Magnetometric Measurement of Susceptibility of Ferro-magnetic Powders
This paper deals with the Magnetometric Measurement of Susceptibility of Ferro-magnetic Powders@IAC
On the Formation and the Magnetic Properties of some Ferrites
This paper deals with the formation and the magnetic properties of some Ferrites@IAC
STUDIES ON CONSTANT PARAMAGNETISM : PART II: Diamagnetic compounds containing a transition element.
@IAC
Discrete Information from CHL Black Holes
AdS_2/CFT_1 correspondence predicts that the logarithm of a Z_N twisted index
over states carrying a fixed set of charges grows as 1/N times the entropy of
the black hole carrying the same set of charges. In this paper we verify this
explicitly by calculating the microscopic Z_N twisted index for a class of
states in the CHL models. This demonstrates that black holes carry more
information about the microstates than just the total degeneracy.Comment: LaTeX file, 24 pages; v2: references adde
BKM Lie superalgebras from counting twisted CHL dyons
Following Sen[arXiv:0911.1563], we study the counting of (`twisted') BPS
states that contribute to twisted helicity trace indices in four-dimensional
CHL models with N=4 supersymmetry. The generating functions of half-BPS states,
twisted as well as untwisted, are given in terms of multiplicative eta products
with the Mathieu group, M_{24}, playing an important role. These multiplicative
eta products enable us to construct Siegel modular forms that count twisted
quarter-BPS states. The square-roots of these Siegel modular forms turn out be
precisely a special class of Siegel modular forms, the dd-modular forms, that
have been classified by Clery and Gritsenko[arXiv:0812.3962]. We show that each
one of these dd-modular forms arise as the Weyl-Kac-Borcherds denominator
formula of a rank-three Borcherds-Kac-Moody Lie superalgebra. The walls of the
Weyl chamber are in one-to-one correspondence with the walls of marginal
stability in the corresponding CHL model for twisted dyons as well as untwisted
ones. This leads to a periodic table of BKM Lie superalgebras with properties
that are consistent with physical expectations.Comment: LaTeX, 32 pages; (v2) matches published versio
Negative discriminant states in N=4 supersymmetric string theories
Single centered BPS black hole solutions exist only when the charge carried
by the black hole has positive discriminant. On the other hand the exact dyon
spectrum in heterotic string theory compactified on T^6 is known to contain
states with negative discriminant. We show that all of these negative
discriminant states can be accounted for as two centered black holes. Thus
after the contribution to the index from the two centered black holes is
subtracted from the total microscopic index, the index for states with negative
discriminant vanishes even for finite values of charges, in agreement with the
results from the black hole side. Bound state metamorphosis -- which requires
us to identify certain apparently different two centered configurations
according to a specific set of rules -- plays a crucial role in this analysis.
We also generalize these results to a class of CHL string theories.Comment: LaTeX file, 32 pages; v2: reference added; v3: added new section 3.
BPS black holes, the Hesse potential, and the topological string
The Hesse potential is constructed for a class of four-dimensional N=2
supersymmetric effective actions with S- and T-duality by performing the
relevant Legendre transform by iteration. It is a function of fields that
transform under duality according to an arithmetic subgroup of the classical
dualities reflecting the monodromies of the underlying string compactification.
These transformations are not subject to corrections, unlike the
transformations of the fields that appear in the effective action which are
affected by the presence of higher-derivative couplings. The class of actions
that are considered includes those of the FHSV and the STU model. We also
consider heterotic N=4 supersymmetric compactifications. The Hesse potential,
which is equal to the free energy function for BPS black holes, is manifestly
duality invariant. Generically it can be expanded in terms of powers of the
modulus that represents the inverse topological string coupling constant,
, and its complex conjugate. The terms depending holomorphically on
are expected to correspond to the topological string partition function and
this expectation is explicitly verified in two cases. Terms proportional to
mixed powers of and are in principle present.Comment: 28 pages, LaTeX, added comment
A Twist in the Dyon Partition Function
In four dimensional string theories with N=4 and N=8 supersymmetries one can
often define twisted index in a subspace of the moduli space which captures
additional information on the partition function than the ones contained in the
usual helicity trace index. We compute several such indices in type IIB string
theory on K3 x T^2 and T^6, and find that they share many properties with the
usual helicity trace index that captures the spectrum of quarter BPS states in
N=4 supersymmetric string theories. In particular the partition function is a
modular form of a subgroup of Sp(2,Z) and the jumps across the walls of
marginal stability are controlled by the residues at the poles of the partition
function. However for large charges the logarithm of this index grows as 1/n
times the entropy of a black hole carrying the same charges where n is the
order of the symmetry generator that is used to define the twisted index. We
provide a macroscopic explanation of this phenomenon using quantum entropy
function formalism. The leading saddle point corresponding to the attractor
geometry fails to contribute to the twisted index, but a Z_n orbifold of the
attractor geometry produces the desired contribution.Comment: LaTeX file, 35 pages; v2: references adde
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