Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Defocusing gravitational microlensing   We introduce the notion of defocusing gravitational lens considering a MACHO
located behind a light source with respect to an observer. The consequence of
defocusing effect is a temporal variability of star luminosity which produces a
gap instead of a peak as tell--tale signature in the light curve. General
theory of (de)focusing rays (geodesics) in a gravitational field is presented.
Furthermore, we give estimations of the mass of the lens and the optical depth
connected to such a phenomenon.

35
The categories of this paper are: mtrl-th
20
The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
23
The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
17
The categories of this paper are: q-fin
2
The categories of this paper are: math
4
The categories of this paper are: cond-mat
22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
13
The categories of this paper are: quant-ph
21
The categories of this paper are: adap-org