Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Regular Stringy Black Holes?   We study the first-order $\alpha'$ corrections to the singular 4-dimensional
massless stringy black holes studied in the nineties in the context of the
Heterotic Superstring. We show that the $\alpha'$ corrections not only induce a
non-vanishing mass and give rise to an event horizon, but also eliminate the
singularity giving rise to a regular spacetime whose global structure includes
further asymptotically flat regions in which the spacetime's mass is positive
or negative. We study the timelike and null geodesics and their effective
potential, showing that the spacetime is geodesically complete. We discuss the
validity of this solution, arguing that the very interesting and peculiar
properties of the solution are associated to the negative energy contributions
coming from the terms quadratic in the curvature. As a matter of fact, the
10-dimensional configuration is singular. We extract some general lessons on
attempts to eliminate black-hole singularities by introducing terms of higher
order in the curvature.

9
The categories of this paper are: nlin
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
12
The categories of this paper are: nucl-th
4
The categories of this paper are: cond-mat