Marco Farina

Marco Farina
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Marco Farina

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High Energy Physics - Phenomenology (24)
High Energy Physics - Experiment (9)
Cosmology and Nongalactic Astrophysics (5)
High Energy Astrophysical Phenomena (2)
High Energy Physics - Theory (1)
Physics - Materials Science (1)

Publications Authored By Marco Farina

Quirks are particles that are both charged under the standard model and under a new confining group. The quirk setup assumes there are no light flavors of the new confining group so that while the theory is in a confining phase, the distance between quirk-antiquirk pairs can be macroscopic. In this work, we reinterpret existing collider limits, those from monojet and heavy stable charged particle searches, as limits on quirks. Read More

We propose a framework in which the QCD axion has an exponentially large coupling to photons, relying on the "clockwork" mechanism. We discuss the impact of present and future axion experiments on the parameter space of the model. In addition to the axion, the model predicts a large number of pseudo-scalars which can be light and observable at the LHC. Read More

We show that high energy measurements of Drell-Yan at the LHC can serve as electroweak precision tests. Dimension-6 operators, from the Standard Model Effective Field Theory, modify the high energy behavior of electroweak gauge boson propagators. Existing measurements of the dilepton invariant mass spectrum, from neutral current Drell-Yan at 8 TeV, have comparable sensitivity to LEP. Read More

A hidden sector with a mass gap undergoes an epoch of cannibalism if number changing interactions are active when the temperature drops below the mass of the lightest hidden particle. During cannibalism, the hidden sector temperature decreases only logarithmically with the scale factor. We consider the possibility that dark matter resides in a hidden sector that underwent cannibalism, and has relic density set by the freeze-out of two-to-two annihilations. Read More

In the context of Twin Higgs models, we study a simple mechanism that simultaneously generates asymmetries in the dark and visible sector through the out-of-equilibrium decay of a TeV scale particle charged under a combination of baryon and twin baryon number. We predict the dark matter to be a 5 GeV twin baryon, which is easy to achieve because of the similarity between the two confinement scales. Dark matter is metastable and can decay to three quarks, yielding indirect detection signatures. Read More

Deviations of the top electroweak couplings from their Standard Model values imply that certain amplitudes for the scattering of third generation fermions and longitudinally polarized vector bosons or Higgses diverge quadratically with momenta. This high-energy growth is a genuine signal of models where the top quark is strongly coupled to the sector responsible for electroweak symmetry breaking. We propose to profit from the high energies accessible at the LHC to enhance the sensitivity to non-standard top-$Z$ couplings, which are currently very weakly constrained. Read More

The ATLAS experiment has recently observed a 3-sigma excess in a channel with a leptonically decaying Z, jets, and ETmiss. It is tantalizing to interpret the signal as the first sign of a natural supersymmetric spectrum. We study such a possibility in a minimal model containing light stops and a neutralino LSP. Read More

LHC searches for fermionic top partners $T$ focus on three decay topologies: $T\to bW$, $T\to tZ$, and $T\to th$. However, top partners may carry new conserved quantum numbers that forbid these decays. The simplest possibility is a conserved parity, under which the top partner is odd and all SM states are even. Read More

We study a natural implementation of Asymmetric Dark Matter in Twin Higgs models. The mirroring of the Standard Model strong sector suggests that a twin baryon with mass around 5 GeV is a natural Dark Matter candidate once a twin baryon number asymmetry comparable to the SM asymmetry is generated. We explore twin baryon Dark Matter in two different scenarios, one with minimal content in the twin sector and one with a complete copy of the SM, including a light twin photon. Read More

We show that the parity of the $h Z\gamma$ vertex can be probed by interference between the gluon fusion Higgs production, $gg \to h \to \gamma Z \to \gamma \ell^+\ell^-$, and the background, $gg \to \gamma Z \to \gamma \ell^+\ell^-$, amplitudes. In the presence of a parity violating $hZ\gamma$ vertex, this interference alters the kinematic distribution of the leptons and photon compared to Standard Model (SM) expectations. For a Higgs with SM-sized width and couplings, we find that the size of the effect enters at most at the $10^{-2}$ level. Read More

A "Higgs factory", an electron-positron collider with center-of-mass energy of about 250 GeV, will measure the cross section of the Higgsstrahlung process, $e^+e^-\rightarrow hZ$, with sub-percent precision. This measurement is sensitive to a variety of new physics scenarios. In this paper, we study two examples. Read More

The exceptional interest in improving the limitations of data storage, molecular electronics, and optoelectronics has promoted the development of an ever increasing number of techniques used to pattern polymers at micro and nanoscale. Most of them rely on Atomic Force Microscopy to thermally or electrostatically induce mass transport, thereby creating topographic features. Here we show that the mechanical interaction of the tip of the Atomic Force Microscope with the surface of a class of conjugate polymers produces a local increase of molecular disorder, inducing a localized lowering of the semiconductor conductivity, not associated to detectable modifications in the surface topography. Read More

We study Higgs boson couplings in the large-$\lambda$ version of the Next-to-Minimal Supersymmetric Standard Model, known as $\lambda$-SUSY. We find that the predicted deviations from the Standard Model (SM) in these couplings are inversely correlated with the amount of fine-tuning needed to accommodate a 126 GeV Higgs. In the most natural regions of parameter space, the 126 GeV Higgs has large admixtures of both the SM-singlet and the non-SM Higgs doublet scalars, and such regions are already ruled out by the LHC. Read More

Many extensions of the Standard Model postulate the existence of new weakly coupled particles, the top partners, at or below the TeV scale. The role of the top partners is to cancel the quadratic divergence in the Higgs mass parameter due to top loops. We point out the generic correlation between naturalness (the degree of fine-tuning required to obtain the observed electroweak scale), and the size of top partner loop contributions to Higgs couplings to photons and gluons. Read More

Motivated by LHC results, we modify the usual criterion for naturalness by ignoring the uncomputable power divergences. The Standard Model satisfies the modified criterion ('finite naturalness') for the measured values of its parameters. Extensions of the SM motivated by observations (Dark Matter, neutrino masses, the strong CP problem, vacuum instability, inflation) satisfy finite naturalness in special ranges of their parameter spaces which often imply new particles below a few TeV. Read More

Current Higgs data show an ambiguity in the value of the Yukawa couplings to quarks and leptons. Not so much because of still large uncertainties in the measurements but as the result of several almost degenerate minima in the coupling profile likelihood function. To break these degeneracies, it is important to identify and measure processes where the Higgs coupling to fermions interferes with other coupling(s). Read More

Electroweak precision measurements established that custodial symmetry is preserved to a good accuracy in the gauge sector after electroweak symmetry breaking. However, recent LHC results might be interpreted as pointing towards Higgs couplings that do not respect such symmetry. Motivated by this possibility, we reconsider the presence of an explicitly custodial breaking coupling in a generic Higgs parameterization. Read More

We reconsider the Higgs bosons discovery potential in the LambdaSUSY framework, in which the masses of the scalar particles are increased already at tree level via a largish supersymmetric coupling between the usual Higgs doublets and a Singlet. We analyze in particular the interplay between the discovery potential of the lightest and of the next-to-lightest scalar, finding that the decay modes of the latter should be more easily detected at the LHC. Read More

We explore the dark matter interpretation of the anomalies claimed by the DAMA and CoGeNT experiments, in conjunction with the various null direct-detection experiments. An independent analysis of the CoGeNT data is employed and several experimental and astrophysical uncertainties are considered. Various phenomenological models are studied, including isospin violating interactions, momentum-dependent form factors, velocity-dependent form factors, inelastic scatterings (endothermic and exothermic) and channeling. Read More

We reconsider the lambda-SUSY model, in which the mass of the Higgs boson is raised already at tree level up to about 200 GeV via an additional interaction in the superpotential between the Higgs bosons and a Singlet, focusing on a scale invariant superpotential. After a detailed analysis of the allowed region in parameter space, which includes constraints coming from the absence of spontaneous CP violation and of unrealistic minima, we study the scalar mass spectrum, the production rate and the decay modes of the lightest scalar, finding that in general both the production rate and the Branching Ratio into gauge bosons can be reduced with respect of those of the standard Higgs, causing it to be hardly detected in the first run of the LHC. Read More

We perform a fit to the recent Xenon100 data and study its implications for Dark Matter scenarios. We find that Inelastic Dark Matter is disfavoured as an explana- tion to the DAMA/LIBRA annual modulation signal. Concerning the scalar singlet DM model, we find that the Xenon100 data disfavors its constrained limit. Read More

In the context of the Supersymmetric Standard Model with hierarchical sfermion masses, we re-analyze the QCD corrections to Delta F=2 effective Hamiltonian properly including effects which have been neglected so far. The point is that some Delta F=2 diagrams, involving both the heavy and the light sparticles, exhibit a logarithmic dependence on the ratio between the two masses, signalling a sensitivity to all the momenta between the two scales. In order to properly deal with these terms one has to take into account the mixing between Delta F=1 and Delta F=2 operators. Read More

In a supersymmetric model with hierarchical squark masses we analyze a pattern of flavour symmetry breaking centered on the special role of the top Yukawa coupling and, by extension, of the full Yukawa couplings for the up-type quarks. For sufficiently heavy squarks of the first and second generation this leads to effective Minimal Flavour Violation of the Flavour Changing Neutral Current amplitudes. For this to happen we determine the bounds on the masses of the heavy squarks with QCD corrections taken into account, properly including previously neglected effects. Read More

Taking a bottom-up point of view and focussing on the lack of signals so far in the Higgs and in the flavour sectors, we argue in favour of giving consideration to supersymmetric extensions of the Standard Model where the lightest Higgs boson has a mass between 200 and 300 GeV and the first two generations of s-fermions are above 20 TeV. After examining the simplest extensions of the Minimal Supersymmetric Standard Model that allow this in a natural way, we summarize the main consequences of this pattern of masses at the LHC and we analyze the consequences of a heavier than normal Higgs boson for Dark Matter. Read More

Motivated by the two candidate Dark Matter events observed by the CDMS experiment, we consider a Constrained Dark Matter Singlet (CDMS) model that, with no free parameters, predicts the DM mass and the DM direct cross section to be in the range weakly favored by CDMS. Read More