Main Contributions by Augusto Sagnotti
JHEP, 2023
We recently constructed type-IIB compactifications to four dimensions depending on a single addit... more We recently constructed type-IIB compactifications to four dimensions depending on a single additional coordinate, where a five-form flux Φ on an internal torus leads to a constant string coupling. Supersymmetry is fully broken when the internal manifold includes a finite interval of length ℓ, which is spanned by a conformal coordinate in a finite range 0 < z < z m. Here we examine the low-lying bosonic spectra and their classical stability, paying special attention to self-adjoint boundary conditions. Special boundary conditions result in the emergence of zero modes, which are determined exactly by first-order equations. The different sectors of the spectrum can be related to Schrödinger operators on a finite interval, characterized by pairs of real constants µ andμ, with µ equal to 1/3 or 2/3 in all cases and different values ofμ. The potentials behave as µ 2 −1/4 z 2 andμ
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JHEP, 2023
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Phys.Lett. B294 (1992) 196-203, Jan 1, 1992
An interesting feature of some open superstring models in D < 10 is the simultaneous presence, in... more An interesting feature of some open superstring models in D < 10 is the simultaneous presence, in the spectrum, of gauge fields and of a number of antisymmetric tensor fields. In these cases the Green-Schwarz mechanism can (and does) take a generalized form, resulting from the combined action of all the antisymmetric tensors. These novelties are illustrated referring to some simple rational models in six dimensions, and some of their implications for the low-energy effective field theory are pointed out.
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Physics Letters B, 1999
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Phys.Lett. B385 (1996) 96-102, Jan 1, 1996
Starting from the type IIB string on the Z orbifold, we construct some chiral open-string vacua w... more Starting from the type IIB string on the Z orbifold, we construct some chiral open-string vacua with N = 1 supersymmetry in four dimensions. The Chan-Paton group depends on the (quantized) NS-NS antisymmetric tensor. The largest choice, SO(8)×SU(12)×U(1), has an anomalous U(1) factor whose gauge boson acquires a mass of the order of the string scale. The corresponding open-string spectrum comprises only Neumann strings and includes three families of chiral multiplets in the (8, 12)+(1, 66) representation. A comparison is drawn with a heterotic vacuum with non-standard embedding, and some properties of the low-energy effective field theory are discussed.
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Phys.Lett. B381 (1996) 97-104, Jan 1, 1996
In non-diagonal conformal models, the boundary fields are not directly related to the bulk spectr... more In non-diagonal conformal models, the boundary fields are not directly related to the bulk spectrum. We illustrate some of their features by completing previous work of Lewellen on sewing constraints for conformal theories in the presence of boundaries. As a result, we include additional open sectors in the descendants of Dodd SU(2) WZW models. A new phenomenon emerges, the appearance of multiplicities and fixed-point ambiguities in the boundary algebra not inherited from the closed sector. We conclude by deriving a set of polynomial equations, similar to those satisfied by the fusion-rule coefficients Nkij , for a new tensor Aiab that determines the open spectrum.
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Phys.Lett. B543 (2002) 303-310, Jan 1, 2002
We show how allowing non-local terms in the field equations of symmetric tensors uncovers a neat ... more We show how allowing non-local terms in the field equations of symmetric tensors uncovers a neat geometry that naturally generalizes the Maxwell and Einstein cases. The end results can be related to multiple traces of the generalized Riemann curvatures Rα1···αs;β1···βs introduced by de Wit and Freedman, divided by suitable powers of the D’Alembertian operator ✷. The conventional local equations can be recovered by a partial gauge fixing involving the trace of the gauge parameters α1···αs−1 , absent in the Fronsdal formulation. The same geometry underlies the fermionic equations, that, for all spins s + 1/2, can be linked via the operator 6∂✷ to those of the spin-s bosons.
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Physics Letters B, 1990
We present a first instance of an exact supersymmetric string vacuum in curved space-time. It cor... more We present a first instance of an exact supersymmetric string vacuum in curved space-time. It corresponds to the Freedman-Gibbons electrovac solution to one version of N=4 supergravity, with N=2 space-tme supersymmetry. The conformal theory includes a Wess-Zumino-Witten model on the SU (1,1) group manifold.
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Phys.Lett. B188 (1987) 58, Jan 1, 1987
We add D fermionic variables to the ends of open strings, generating the combinatoric and group t... more We add D fermionic variables to the ends of open strings, generating the combinatoric and group theory factors of SO(2 tD/21). Thus 10 variables give SO(32). The results are illustrated by a one'-loop calculation, giving the partition function of the theory. We discuss boundary conditions, and the modifications of the Feynman rules needed for obtaining the groups U(2 [D/2]) and USp(2ID/2]).
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Phys.Lett. B694 (2010) 80-88
"In string models with “brane supersymmetry breaking” exponential potentials emerge at (closed-st... more "In string models with “brane supersymmetry breaking” exponential potentials emerge at (closed-string)
tree level but are not accompanied by tachyons. Potentials of this type have long been a source of
embarrassment in flat space, but can have interesting implications for Cosmology. For instance, in ten
dimensions the logarithmic slope |V'/V | lies precisely at a “critical” value where the Lucchin–Matarrese
attractor disappears while the scalar field is forced to climb up the potential when it emerges from
the Big Bang. This type of behavior is in principle perturbative in the string coupling, persists after
compactification, could have trapped scalar fields inside potential wells as a result of the cosmological
evolution and could have also injected the inflationary phase of our Universe."
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Nuclear Physics B, 2004
We discuss string spectra in the low-tension limit using the BRST formalism, with emphasis on the... more We discuss string spectra in the low-tension limit using the BRST formalism, with emphasis on the role of triplets of totally symmetric tensors and spinor-tensors and their generalizations to cases with mixed symmetry and to (A)dS backgrounds. We also present simple ...
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Phys.Lett. B247 (1990) 517-524, Jan 1, 1990
We clarify the role of the fusion algebra in determining the interactions and the Chan-Paton symm... more We clarify the role of the fusion algebra in determining the interactions and the Chan-Paton symmetry of open-string models. Adapting the internal symmetry to the fusion algebra yields corresponding patterns of symmetry breaking, which we illustrate in a number of examples.
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Phys.Rept. 371 (2002) 1-150, Erratum-ibid. 376 (2003) 339-405, Jan 1, 2002
This review is devoted to open strings, and in particular to the often surprising features of the... more This review is devoted to open strings, and in particular to the often surprising features of their spectra. It follows and summarizes developments that took place mainly at the University of Rome “Tor Vergata” over the last decade, and centred on world-sheet aspects of the constructions now commonly referred to as “orientifolds”. Our presentation aims to bridge the gap between the world-sheet analysis, that first exhibited many of the novel features of these systems, and their geometric description in terms of extended objects, D-branes and O-planes, contributed by many other colleagues, and most notably by J. Polchinski. We therefore proceed through a number of prototype examples, starting from the bosonic string and moving on to tendimensional fermionic strings and their toroidal and orbifold compactifications, in an attempt to guide the reader in a self-contained journey to the more recent developments related to the breaking of supersymmetry.
Dedicated to John H. Schwarz on the occasion of his sixties birthday
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Arxiv preprint hep-th/0208020, Jan 1, 2002
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Phys.Lett. B216 (1989) 59, Jan 1, 1989
""We discuss twistings of open strings and corresponding Z2 (target space) orbifold solutions. As... more ""We discuss twistings of open strings and corresponding Z2 (target space) orbifold solutions. As for the bosonic SO (8192 ) model
and for the SO(32) superstring, the proper group theory rules involve suitable powers of two related to the geometry of the
parameter space.""
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Phys.Lett. B160 (1985) 81, Jan 1, 1985
We show that the S matrix of pure Einstein gravity diverges at the two-loop order in four dimensions
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Arxiv preprint hep-th/9509080 - Presented at SUSY 95, Jan 1, 1995
Open-string theories may be related to suitable models of oriented closed strings. The resulting ... more Open-string theories may be related to suitable models of oriented closed strings. The resulting construction of “open descendants” is illustrated in a few simple cases that exhibit some of its key features.
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Nucl.Phys.Proc.Suppl. 56B (1997) 332-343, Jan 1, 1997
The perturbative analysis of models of open and closed superstrings presents a number of surprise... more The perturbative analysis of models of open and closed superstrings presents a number of surprises. For instance, variable numbers of antisymmetric tensors ensure their consistency via generalized Green-Schwarz cancellations and a novel type of singularity occurs in their moduli spaces. All these features are related, in one way or another, to the presence of boundaries on the world sheet or, equivalently, of extended objects (branes) interacting with the bulk theory in space time. String dualities have largely widened the interest in these models, that exhibit a wealth of generic non-perturbative features of String Theory.
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Main Contributions by Augusto Sagnotti
tree level but are not accompanied by tachyons. Potentials of this type have long been a source of
embarrassment in flat space, but can have interesting implications for Cosmology. For instance, in ten
dimensions the logarithmic slope |V'/V | lies precisely at a “critical” value where the Lucchin–Matarrese
attractor disappears while the scalar field is forced to climb up the potential when it emerges from
the Big Bang. This type of behavior is in principle perturbative in the string coupling, persists after
compactification, could have trapped scalar fields inside potential wells as a result of the cosmological
evolution and could have also injected the inflationary phase of our Universe."
Dedicated to John H. Schwarz on the occasion of his sixties birthday
and for the SO(32) superstring, the proper group theory rules involve suitable powers of two related to the geometry of the
parameter space.""
tree level but are not accompanied by tachyons. Potentials of this type have long been a source of
embarrassment in flat space, but can have interesting implications for Cosmology. For instance, in ten
dimensions the logarithmic slope |V'/V | lies precisely at a “critical” value where the Lucchin–Matarrese
attractor disappears while the scalar field is forced to climb up the potential when it emerges from
the Big Bang. This type of behavior is in principle perturbative in the string coupling, persists after
compactification, could have trapped scalar fields inside potential wells as a result of the cosmological
evolution and could have also injected the inflationary phase of our Universe."
Dedicated to John H. Schwarz on the occasion of his sixties birthday
and for the SO(32) superstring, the proper group theory rules involve suitable powers of two related to the geometry of the
parameter space.""
Adaptation française : ateliers de traduction 2018, Faculté de Traduction et d’Interprétation – UMONS
(Contribution to CERN Courier, Jan/Feb. 2017)
phenomenon and the low–ℓ CMB. For the first 32 multipoles, combining the hard exponential with a milder one leading to ns ≃ 0.96 and with a small gaussian bump we have attained a reduction of χ2 to about 46% of the standard Lambda-CDM setting, with both WMAP9 and PLANCK 2013 data. This result corresponds to a χ2/DOF of about 0.45, to be compared with a Lambda-CDM value of about 0.85. The preferred choices combine naturally quadrupole depression, a first peak around ℓ = 5 and a wide minimum around ℓ = 20. We have also gathered some evidence that similar spectra emerge if the hard exponential is combined with more realistic models of inflation.
A problem of the preferred examples is their slow convergence to an almost scale–invariant profile.
supported by a scalar field driven by an exponential potentia
l. If, as in String Theory, this potential is steep enough, under some assumptions that are spelled out in the text the scalar can only climb up as it emerges from an initial singularity. In the presence of another mild exponential, slow–roll inflation is thus injected during the ensuing descent and definite imprints are left in the CMB power spectrum: the quadrupole is systematically reduced and, depending on the choice of two parameters, an oscillatory behavior can also emerge for low multipoles l<50, in qualitative agreement with WMAP9 and PLANCK data.
still well off its eventual attractor. If a pre-inflationary climbing phase of this type had occurred within 6-7 e–folds of the horizon exit for the largest observable wavelengths, displacement off the attractor and initial–state effects would conspire to suppress power in the primordial scalar
spectrum, enhancing it in the tensor spectrum and typically superposing oscillations on both. We investigate these imprints on CMB observables over a range of parameters, examine their statistical significance, and provide a semi–analytic rationale for our results. It is tempting to ascribe at least part of the large-angle anomalies in the CMB to pre–inflationary dynamics of
this type."
tensor are interchanged via Poincar´e duality. We show how this phenomenon extends to D space–time dimensions for non–linear actions involving pairs of forms of rank p and D−p−2. As a byproduct, we construct a new two–field generalization of the Born–Infeld action whose equations of motion are invariant under a U(1) duality. In these systems, the introduction of Green–Schwarz terms results in explicit non–linear mass–like terms for dual massive pairs.
inflation. However, as an aside we also review briefly some interesting two–field extensions
of the Born–Infeld Lagrangian whose field equations enjoy extended duality symmetries.
by C. Heissenberg and A. Sagnotti (Cambridge University Press, 2022)