8 research outputs found
Axion minima in string theory
No full textAbstract We study the landscape of axion theories in compactifications of type IIB string theory on orientifolds of Calabi-Yau threefolds. In a sample of approximately 400,000 geometries we find that in the regime of perturbative control there are only a handful of distinct axion minima per geometry, despite there being infinitely many instanton contributions to the potential with unbounded charges. The ensemble we consider has numbers of axion fields ranging from 1 to 491, but the median number of distinct minima is 1, the mean number is 1.9 and the largest is 54. These small numbers of minima occur because the leading axion charge matrix is quite sparse, while the subleading corrections are increasingly exponentially suppressed as the charges increase. On their own, such potentials are nowhere near rich enough to be of interest anthropically. This is in stark contrast to potentials for which the charge matrix is less sparse or the hierarchies between the instanton contributions are less steep, where one can find O 10 500 minima for O 500 axions. To generate a sufficiently large landscape from string compactifications our results indicate that one would need to rely on varying flux or topology, or to develop tools that allow one to go beyond the regime we can control with current techniques
Superradiance in string theory
No full textWe perform an extensive analysis of the statistics of axion masses and interactions in compactifications of type IIB string theory, and we show that black hole superradiance excludes some regions of Calabi-Yau moduli space. Regardless of the cosmological model, a theory with an axion whose mass falls in a superradiant band can be probed by the measured properties of astrophysical black holes, unless the axion self-interaction is large enough to disrupt formation of a condensate. We study a large ensemble of compactifications on Calabi-Yau hypersurfaces, with 1 ≤ h 1,1 ≤ 491 closed string axions, and determine whether the superradiance conditions on the masses and self-interactions are fulfilled. The axion mass spectrum is largely determined by the Kahler parameters, for mild assumptions about the contributing instantons, and takes a nearly-universal form when h 1,1 ≫ 1. When the Kahler moduli are taken at the tip of the stretched Kahler cone, the fraction of geometries excluded initially grows with h 1,1, to a maximum of ≈ 0.5 at h 1,1 ≈ 160, and then falls for larger h 1,1. Further inside the Kahler cone, the superradiance constraints are far weaker, but for h 1,1 ≫ 100 the decay constants are so small that these geometries may be in tension with astrophysical bounds, depending on the realization of the Standard Model.</p
Light U(1)s in heterotic string models
No full textWe present the construction of heterotic string models built using the free fermionic formulation, and focus on how additional U(1)s may arise. We motivate an anomaly free combination, U(1)_\zeta, as a proton lifetime preserving symmetry external to a left--right symmetric gauge group. This same combination is found to nullify lepton number in U(1)_{B-L} to form a leptophobic combination, also in left--right symmetric models, which we compare to other leptophobic U(1) combinations constructed in the context of different gauge groups.
We then accommodate U(1)_\zeta as a proton lifeguard symmetry in an effective field theory. We present a comparative study of how gauge coupling unification constraints may be satisfied when SO(10)xU(1)_\zeta\not\subset E_6 and when the U(1)_\zeta charges do have an E_6 embedding. We show that without such an embedding, current values of \sin^2\theta_W(M_Z) and \alpha_3(M_Z) rule these models out. We go on to discuss how viable string models with this property included may be constructed
Proton stability and light<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>Z</mml:mi><mml:mo>′</mml:mo></mml:msup></mml:math>inspired by string derived models
No full textLeptophobic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:msup><mml:mi>Z</mml:mi><mml:mo>′</mml:mo></mml:msup></mml:math> in heterotic-string derived models
No full textProton stability, gauge coupling unification, and a light Z′ in heterotic-string models
No full textWe explore the phenomenological viability of a light Z′ in heterotic-string models, whose existence has been motivated by proton stability arguments. A class of quasirealistic string models that produce such a viable Z′ are the left-right symmetric (LRS) heterotic-string models in the free fermionic formulation. A key feature of these models is that the matter charges under U(1)Z′ do not admit an E6 embedding. The light Z′ in the LRS heterotic-string models forbids baryon number violating operators, while allowing lepton number violating operators, hence suppressing proton decay yet allowing for sufficiently small neutrino masses via a seesaw mechanism. We show that the constraints imposed by the gauge coupling data and heterotic-string coupling unification nullify the viability of a light Z′ in these models. We further argue that agreement with the gauge coupling data necessitates that the U(1)Z′ charges admit an E6 embedding. We discuss how viable string models with this property may be constructed. © 2013 American Physical Society
Axion minima in string theory
No full textWe study the landscape of axion theories in compactifications of type IIB
string theory on orientifolds of Calabi-Yau threefolds. In a sample of
approximately 400,000 geometries we find that in the regime of perturbative
control there are only a handful of distinct axion minima per geometry, despite
there being infinitely many instanton contributions to the potential with
unbounded charges. The ensemble we consider has numbers of axion fields ranging
from 1 to 491, but the median number of distinct minima is 1, the mean number
is 1.9 and the largest is 54. These small numbers of minima occur because the
leading axion charge matrix is quite sparse, while the subleading corrections
are increasingly exponentially suppressed as the charges increase. On their
own, such potentials are nowhere near rich enough to be of interest
anthropically. This is in stark contrast to potentials for which the charge
matrix is less sparse or the hierarchies between the instanton contributions
are less steep, where one can find minima for
axions. To generate a sufficiently large landscape from
string compactifications our results indicate that one would need to rely on
varying flux or topology, or to develop tools that allow one to go beyond the
regime we can control with current techniques.Comment: 14+6 pages, 1 figur
Environmental sustainability in basic research: a perspective from HECAP+
No full textInternational audienceThe climate crisis and the degradation of the world's ecosystems require humanity to take immediate action. The international scientific community has a responsibility to limit the negative environmental impacts of basic research. The HECAP+ communities (High Energy Physics, Cosmology, Astroparticle Physics, and Hadron and Nuclear Physics) make use of common and similar experimental infrastructure, such as accelerators and observatories, and rely similarly on the processing of big data. Our communities therefore face similar challenges to improving the sustainability of our research. This document aims to reflect on the environmental impacts of our work practices and research infrastructure, to highlight best practice, to make recommendations for positive changes, and to identify the opportunities and challenges that such changes present for wider aspects of social responsibility
