IRIS Università degli Studi di Bolognahttps://cris.unibo.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Wed, 02 Dec 2020 07:16:09 GMT2020-12-02T07:16:09Z10661String moduli inflation: an overviewhttp://hdl.handle.net/11585/510185Titolo: String moduli inflation: an overview
Abstract: We present an overview of inflationary models derived from string theory focusing mostly on closed string moduli as inflatons. After a detailed discussion of the η-problem and different approaches to address it, we describe possible ways to obtain a de Sitter vacuum with all closed string moduli stabilized. We then look for inflationary directions and present some of the most promising scenarios where the inflatons are either the real or the imaginary part of Kahler moduli. We pay particular attention on extracting potential observable implications, showing how most of the scenarios predict negligible gravitational waves and could therefore be ruled out by the Planck satellite. We conclude by briefly mentioning some open challenges in string cosmology beyond deriving
just inflation.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/11585/5101852011-01-01T00:00:00ZTesting anisotropic string compactifications in the labhttp://hdl.handle.net/11585/510186Titolo: Testing anisotropic string compactifications in the lab
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11585/5101862012-01-01T00:00:00ZAnisotropic modulus stabilisation: strings at LHC scales with micron-sized extra dimensionshttp://hdl.handle.net/11585/510176.1Titolo: Anisotropic modulus stabilisation: strings at LHC scales with micron-sized extra dimensions
Abstract: We construct flux-stabilised Type IIB string compactifications whose extra dimensions have very different sizes, and use these to describe several types of vacua with a TeV string scale. Because we can access regimes where two dimensions are hierarchically larger than the other four, we find examples where two dimensions are micron-sized while
the other four are at the weak scale in addition to more standard examples with all six extra dimensions equally large. Besides providing ultraviolet completeness, the phenomenology of these models is richer than vanilla large-dimensional models in several generic ways: (i)
they are supersymmetric, with supersymmetry broken at sub-eV scales in the bulk but only nonlinearly realised in the Standard Model sector, leading to no MSSM superpartners for ordinary particles and many more bulk missing-energy channels, as in supersymmetric large extra dimensions (SLED); (ii) small cycles in the more complicated extra-dimensional geometry allow some KK states to reside at TeV scales even if all six extra dimensions are nominally much larger; (iii) a rich spectrum of string and KK states at TeV scales; and (iv) an equally rich spectrum of very light moduli exist having unusually small (but technically natural) masses, with potentially interesting implications for cosmology and astrophysics that nonetheless evade new-force constraints. The hierarchy problem is solved in these models because the extra-dimensional volume is naturally stabilised at exponentially large values: the extra dimensions are Calabi-Yau geometries with a 4D K3 or T^4-fibration over a 2D base, with moduli stabilised within the well-established LARGE-Volume scenario. The new technical step is the use of poly-instanton corrections to the superpotential (which, unlike for simpler models, are likely to be present on K3 or T^4-fibered Calabi-Yau compactifications) to obtain a large hierarchy between the sizes of different dimensions. For several scenarios we identify the low-energy spectrum and briefly discuss some of their astrophysical, cosmological and phenomenological implications.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/11585/510176.12011-01-01T00:00:00ZLARGE volume string compactifications at finite temperaturehttp://hdl.handle.net/11585/510181Titolo: LARGE volume string compactifications at finite temperature
Abstract: We present a detailed study of the finite-temperature behaviour of the LARGE Volume type IIB flux compactifications. We show that certain moduli can thermalise at high temperatures. Despite that, their contribution to the finite-temperature effective potential is always negligible and the latter has a runaway behaviour. We compute the maximal temperature T_max, above which the internal space decompactifies, as well as the temperature T_∗, that is reached after the decay of the heaviest moduli. The natural constraint T_∗ < T_max
implies a lower bound on the allowed values of the internal volume V. We find that this restriction rules out a significant range of values corresponding to smaller volumes of the order V ∼ 10^4, which lead to standard GUT theories. Instead, the bound favours values of the
order V ∼ 10^15, which lead to TeV scale SUSY desirable for solving the hierarchy problem. Moreover, our result favours low-energy inflationary scenarios with density perturbations generated by a field, which is not the inflaton. In such a scenario, one could achieve both inflation and TeV-scale SUSY, although gravity waves would not be observable. Finally, we pose a two-fold challenge for the solution of the cosmological moduli problem. First, we show that the heavy moduli decay before they can begin to dominate the energy density of the Universe. Hence they are not able to dilute any unwanted relics. And second, we argue that,
in order to obtain thermal inflation in the closed string moduli sector, one needs to go beyond the present EFT description.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/11585/5101812009-01-01T00:00:00ZA note on the magnitude of the flux superpotentialhttp://hdl.handle.net/11585/227276.1Titolo: A note on the magnitude of the flux superpotential
Abstract: The magnitude of the flux superpotential W flux plays a crucial role in determining the scales of IIB string compactifications after moduli stabilisation. It has been argued that values of W flux ≪ 1 are preferred, and even required for physical and consistency reasons. This note revisits these arguments. We establish that the couplings of heavy Kaluza-Klein modes to light states scale with the internal volume as g ~ M_{KK} /M_{P} ~ V^{−2/3} ≪ 1 and argue that consistency of the superspace derivative expansion requires gF/M^2 ~ m_{3/2} /M_{KK} ≪ 1, where F is the auxiliary field of the light fields and M the ultraviolet cutoff. This gives only a mild constraint on the flux superpotential, W flux ≪ V^{1/3}, which can be easily satisfied for O (1) values of W flux. This regime is also statistically favoured and makes the Bousso-Polchinski mechanism for the vacuum energy hierarchically more efficient.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11585/227276.12014-01-01T00:00:00ZA geometrical upper bound on the inflaton rangehttp://hdl.handle.net/11585/645422.1Titolo: A geometrical upper bound on the inflaton range
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/11585/645422.12018-01-01T00:00:00ZPrimordial black holes from string inflationhttp://hdl.handle.net/11585/643861.1Titolo: Primordial black holes from string inflation
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/11585/643861.12018-01-01T00:00:00Zα′ Inflation: moduli stabilisation and observable tensors from higher derivativeshttp://hdl.handle.net/11585/570239Titolo: α′ Inflation: moduli stabilisation and observable tensors from higher derivatives
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11585/5702392016-01-01T00:00:00ZDark radiation in LARGE volume modelshttp://hdl.handle.net/11585/338719Titolo: Dark radiation in LARGE volume models
Abstract: We consider reheating driven by volume modulus decays in the LARGE volume scenario. Such reheating always generates nonzero dark radiation through the decays to the axion partner, while the only competitive visible sector decays are Higgs pairs via the Giudice-Masiero term. In the framework of sequestered models where the cosmological moduli problem is absent, the simplest model with a shift-symmetric Higgs sector generates 1.56≤ΔNeff≤1.74. For more general cases, the known experimental bounds on ΔNeff strongly constrain the parameters and matter content of the models.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/11585/3387192013-01-01T00:00:00ZJust enough inflation: power spectrum modifications at large scaleshttp://hdl.handle.net/11585/408803Titolo: Just enough inflation: power spectrum modifications at large scales
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11585/4088032014-01-01T00:00:00Z