29 research outputs found
Aspects of finite temperature corrections in string theory
PhDIn this thesis some aspects of temperature corrections in string theory are analyzed: in
particular, we study the thermal contributions to the 4 dimensional effective potential
arising from string theory compactifications.
String theory predicts that the spacetime has more than 4 dimensions; in particular,
supersymmetric string theories are consistent only if the spacetime has 10 dimensions,
1 time plus 9 space directions. In order to describe the physics of our Universe
with string theory we make 6 spatial directions very small, namely, we curl them
into a 6-dimensional space. The resulting 4-dimensional theory depends on a large
number of parameters which are massless scalar fields called moduli. The different
values that the moduli can take represent both the possible deformations of the 6-
dimensional compact space and the values of the coupling constants and masses in
the 4-dimensional spacetime. Allowing them to have arbitrary values leads to a lack
of predictability of various 4D physical quantities, to a huge vacuum degeneracy and
to unobserved long range fifth forces.
In the thesis we review some methods established in the literature in order to fix the moduli values and hence to fix a particular geometry and we investigate how
the inclusion of temperature corrections alter their values and affect the geometry
of the compact space. The analysis seems to suggest that at least in the specific
compactification scenarios considered in this thesis, temperature corrections do not
alter substantially the zero temperature results.
In the final part of this work, we analyze instead an example in which the inclusion
of temperature corrections alters dramatically the picture at zero temperature. In
particular, we study an unstable system constituted by a pair of Dirichlet (D) and
anti-D brane that, although being unstable at zero temperature, it can become stable
once finite temperature corrections are switched on
Aminium Salts Induced Desulphurization of Allyl and Diallyl Thiiranes. Synthesis of Dienes and Trienes
Catalytic amounts of aminium salts A-U induct the conversion of methylene chloride in
solutions of several ally1 and diallyl episulphidcs 1-6 into the corresponding unsaturated derivatives 7-
12. The desulphuriwtion process, which occurs through a plausible chain electron-transfer mechanism,
rapid and may proceed in a fashiont hat preservest he stereochemistryo f the starting episulphide
Allylated Ketosulphides of Benzothiazole as Intermediates for Stereoselective Synthesis of Allyl Ketones, Allyl Thiiranes and Dienes
alfa-Ketosulphides of benzothiazole 1 react with allylic carbonates in the presence of
palladium acetate in dichloromethane under mild conditions affording alfa- and alfa,alfa-diallylated
ketosulphides 2 in high yields. Reductive desulphurization of 2a-d with tributyltin hydride gives
diallylated ketones 3s-d, whereas reduction of mono-allylated Ze-k with sodium borohydride in
isopropanol affords ally1 episulphides 4e-k prevalently as (Z)-isomers which can be transformed
stcteoselectively into dienes
Stereoselective Synthesis of Electrophilic Spirocyclopropanes in Ionic Liquids
The reaction of b-oxosulfides of benzothiazole with Michael acceptors, in liquid tetrabutylammonium
bromide and sodium bicarbonate as base, allows a stereoselective synthesis of spirocyclopropane