arXiv subjects

Fabio Zwirner

Publications and source records attributed to Fabio Zwirner.

At least 19 recordsLinked to original sources

arXiv2025

Supersymmetry-breaking compactifications on Riemann-flat manifolds

We consider compactifications of higher-dimensional supergravities on Riemann-flat manifolds of dimension d ($3 \le d \le 7$) that fully break supersymmetry at the classical level on a resulting D-dimensional Minkowski space. We systematically discuss consistency conditions, the Kaluza-Klein (KK) spectrum and harmonics, and the resulting one-loop effective potential $V_1$, focusing for illustration on maximal supergravity and d=3, in particular on the $T^3/Z_3$ and on the Hantzsche-Wendt manifolds. We show how the KK spectrum is organized in multiplets of the broken supersymmetry, derive new universal supertrace mass relations valid at each KK level and obtain an analytic finite expression for $V_1$ after resumming the contributions of all KK levels. In all examples $V_1$ is negative definite and scales with inverse powers of some internal radii. We extensively comment, when applicable, on the relation with the Scherk-Schwarz mechanism and with supersymmetry-breaking string compactifications on freely acting symmetric orbifolds. We also finally clarify the assumptions and constraints for Scherk-Schwarz reductions to correspond to twisted tori compactifications.

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arXiv2025

No-scale supergravity

To connect supergravity with the real world, a highly non-trivial requirement is complete spontaneous supersymmetry breaking in an approximately flat four-dimensional space-time. In no-scale supergravity models, this naturally happens at the classical level: the gravitino mass, setting the scale of supersymmetry breaking, slides along a flat direction of the potential with vanishing energy. This contribution briefly describes, with a personal selection of simple illustrative examples, some qualitative features of no-scale models that relate them to a possible dynamical generation of the hierarchies between the vacuum energy scale, the weak scale and the Planck scale. It includes comments on their versions with extended supersymmetry, on their higher-dimensional origin and on how their still unsolved problems of quantum stability can already be addressed, with some results, at the level of supergravity compactifications, although their solution (if any) will eventually require a better understanding of superstring theories.

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arXiv2024

One-loop effective potential in Scherk-Schwarz compactifications of pure d=5 supergravities

We perform a systematic analysis of the one-loop effective potential of pure $d=5$ supergravities, with supersymmetry fully broken by a Scherk-Schwarz compactification on the circle, as a function of the radial modulus. We discuss the precise correspondence between the effective potential $V_1$ in the full compactified theory and its counterpart $V_{1,red}$ in the reduced theory. We confirm that $V_1$ is finite for any $N>0$, in contrast to $V_{1,red}$. We find that for broken $N=8$ supergravity $V_1$ is negative definite even after accounting for the Kaluza-Klein states. We outline a program for future work where the study of a different kind of Scherk-Schwarz compactifications, still at the field theory level but with at least three extra dimensions, could lead to qualitatively new results.

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arXiv2015

Minimal scalar-less matter-coupled supergravity

We build the minimal supergravity model where the nilpotent chiral goldstino superfield is coupled to a chiral matter superfield, realising a different non-linear representation through a mixed nilpotency constraint. The model describes the spontaneous breaking of local supersymmetry in the presence of a generically massive Majorana fermion, but in the absence of elementary scalars. The sign and the size of the cosmological constant, the spectrum and the four-fermion interactions are controlled by suitable parameters.

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arXiv2015

Robust collider limits on heavy-mediator Dark Matter

We discuss how to consistently use Effective Field Theories (EFTs) to set universal bounds on heavy-mediator Dark Matter at colliders, without prejudice on the model underlying a given effective interaction. We illustrate the method for a Majorana fermion, universally coupled to the Standard Model quarks via a dimension-6 axial-axial four-fermion operator. We recast the ATLAS mono-jet analysis and show that a considerable fraction of the parameter space, seemingly excluded by a naïve EFT interpretation, is actually still unexplored. Consistently set EFT limits can be reinterpreted in any specific underlying model. We provide two explicit examples for the chosen operator and compare the reach of our model-independent method with that obtainable by dedicated analyses.

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arXiv2014

On sgoldstino-less supergravity models of inflation

We go a step further in the search for a consistent and realistic supergravity model of large-field inflation by building a class of models with the following features: during slow-roll, all the scalar fields other than the inflaton are frozen by large inflaton-dependent masses or removed from the spectrum; at the end of inflation, supersymmetry is spontaneously broken with naturally vanishing classical vacuum energy. We achieve this by combining some geometrical properties of the Kaehler potential with the consistent use of a single nilpotent chiral superfield, in one-to-one correspondence with the supersymmetry-breaking direction in field space at the vacuum.

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arXiv2014

Geometrical hierarchies in classical supergravity

We introduce a $N=1$ supergravity model with a very simple hidden sector coupled to the electroweak gauge and Higgs sectors of the MSSM. At the classical level, supersymmetry and $SU(2)\times U(1)$ are both spontaneously broken, with vanishing vacuum energy. Two real flat directions control the two symmetry-breaking scales $m_{3/2}$ and $m_Z$. The two massless scalars are a gauge singlet and the standard Higgs boson. All other unobserved particles have masses of order $m_{3/2}$. This may be a new starting point for studying the compatibility of naturalness with the observed mass hierarchies.

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arXiv2013

A new class of N=1 no-scale supergravity models

We introduce a new N=1 no-scale supergravity model with F- and D-term breaking. It contains a single chiral supermultiplet T and a single U(1) vector multiplet U, gauging an axionic shift symmetry. Both supersymmetry and the gauge symmetry are spontaneously broken, with the spin-3/2, spin-1 and spin-1/2 masses sliding along a classical flat direction, with a single real massless scalar in the spectrum. The other degrees of freedom are absorbed by the massive gravitino and vector. We extend our model, under very mild conditions, to general gauge groups and matter content.

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arXiv2013

Theory Summary

Talk given at the XLVIII Rencontres de Moriond, Electroweak Interactions and Unified Theories, La Thuile, Italy, 2-9 March 2013, to appear in the Proceedings.

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arXiv2013

On the moduli space of spontaneously broken N = 8 supergravity

We analyze the moduli space of spontaneously broken N=8 supergravity theories in 4 dimensions with classical Minkowski vacua. We find that all the known classical vacua, as well as the several new ones we construct here, can be connected by sending some of the moduli to their boundary values. We also show that Cremmer-Scherk-Schwarz models can be viewed as special limits of more general CSO* gaugings, which allow for non-Abelian residual symmetries on the vacuum. Finally, we find that all the classical Minkowski vacua with fully broken supersymmetry found so far are unstable with respect to 1-loop corrections, which drive the effective potential to negative values.

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arXiv2013

Quantum corrections to broken N=8 supergravity

The discovery of the Higgs boson and the non-discovery (so far) of additional particles at the TeV scale underline our poor understanding of the hierarchy problems in the physics of the fundamental interactions. Loosely motivated by this consideration, I review some recent results on the classical and quantum stability of Minkowski vacua in spontaneously broken N=8 supergravity.

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arXiv2012

Quantum corrections to broken N = 8 supergravity

We show that the one-loop effective potential of spontaneously broken N=8 supergravity is calculable and finite at all classical four-dimensional Minkowski vacua without tachyons in the spectrum. The reason is that the supertraces of the quadratic and quartic mass matrices vanish along the classically flat directions: Str M^2 = Str M^4 =0. We also show that Str M^6 = 0 but Str M^8 > 0 in a broad class of vacua with broken supersymmetry on a flat background, which includes all those explicitly identified so far. We find analytical and numerical evidence that the corresponding one-loop effective potential is negative-definite.

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arXiv2011

On Fayet-Iliopoulos terms and de Sitter vacua in supergravity: some easy pieces

We clarify a number of issues on Fayet-Iliopoulos (FI) terms in supergravity, keeping the formalism at a minumum and making use of explicit examples. We explain why, if the U(1) vector is massive everywhere in field space, FI terms are not genuine and can always be redefined away or introduced when they are not present. We formulate a simple anomaly-free model with a genuine FI term, a classically stable de Sitter (dS) vacuum and no global symmetries. We explore the relation between N=2 and N=1 FI terms by discussing N=1 truncations of N=2 models with classically stable dS vacua.

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arXiv2009

Non-universal minimal Z' models: present bounds and early LHC reach

We consider non-universal 'minimal' Z' models, whose additional U(1) charge is a non-anomalous linear combination of the weak hypercharge Y, the baryon number B and the partial lepton numbers (L_e, L_mu, L_tau), with no exotic fermions beyond three standard families with right-handed neutrinos. We show that the observed pattern of neutrino masses and mixing can be fully reproduced by a gauge-invariant renormalizable Lagrangian, and flavor-changing neutral currents in the charged lepton sector are suppressed by a GIM mechanism. We then discuss the phenomenology of some benchmark models. The electrophilic B-3L_e model is significantly constrained by electroweak precision tests, but still allows to fit the hint of an excess observed by CDF in dielectrons but not in dimuons. The muonphilic B-3L_mu model is very mildly constrained by electroweak precision tests, so that even the very early phase of the LHC can explore significant areas of parameter space. We also discuss the hadrophobic L_mu-L_tau model, which has recently attracted interest in connection with some puzzling features of cosmic ray spectra.

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arXiv2009

Minimal Z' models: present bounds and early LHC reach

We consider `minimal' Z' models, whose phenomenology is controlled by only three parameters beyond the Standard Model ones: the Z' mass and two effective coupling constants. They encompass many popular models motivated by grand unification, as well as many arising in other theoretical contexts. This parameterization takes also into account both mass and kinetic mixing effects, which we show to be sizable in some cases. After discussing the interplay between the bounds from electroweak precision tests and recent direct searches at the Tevatron, we extend our analysis to estimate the early LHC discovery potential. We consider a center-of-mass energy from 7 towards 10 TeV and an integrated luminosity from 50 to several hundred pb^-1, taking all existing bounds into account. We find that the LHC will start exploring virgin land in parameter space for M_Z' around 700 GeV, with lower masses still excluded by the Tevatron and higher masses still excluded by electroweak precision tests. Increasing the energy up to 10 TeV, the LHC will start probing a wider range of Z' masses and couplings, although several hundred pb^-1 will be needed to explore the regions of couplings favored by grand unification and to overcome the Tevatron bounds in the mass region around 250 GeV.

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arXiv2009

Type-IIA flux compactifications and N=4 gauged supergravities

We establish the precise correspondence between Type-IIA flux compactifications preserving an exact or spontaneously broken N=4 supersymmetry in four dimensions, and gaugings of their effective N=4 supergravities. We exhibit the explicit map between fluxes and Bianchi identities in the higher-dimensional theory and generalized structure constants and Jacobi identities in the reduced theory, also detailing the origin of gauge groups embedded at angles in the duality group. We present AdS4 solutions of the massive Type-IIA theory with spontaneous breaking to N=1, at small string coupling and large volume, and discuss their dual CFT3.

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arXiv2007

On general flux backgrounds with localized sources

We derive new consistency conditions for string compactifications with generic fluxes (RR, NSNS, geometrical) and localized sources (D-branes, NS-branes, KK-monopoles). The constraints are all related by string dualities and share a common origin in M-theory. We also find new sources of instabilities. We discuss the importance of these conditions for the consistency of the effective action and for the study of interpolating solutions between vacua.

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arXiv2007

Beyond Twisted Tori

Exploiting the fact that Kaluza-Klein monopoles and the associated generalized orbifold planes are sources for geometrical fluxes, omega, we show that the standard constraint omega.omega=0, valid for superstring compactifications on twisted tori, can be consistently relaxed. This leads to novel possibilities for constructing superstring models with fluxes and localized sources, as well as for stabilizing moduli. This also explains the ten-dimensional origin of a family of N=4 gauged supergravities, whose interpretation in type-IIA orientifold compactifications was lacking.

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