arXiv subjects

Jure Zupan

Publications and source records attributed to Jure Zupan.

At least 109 records · Page 6Linked to original sources

arXiv2013

Constraints on CP-violating Higgs couplings to the third generation

Discovering CP-violating effects in the Higgs sector would constitute an indisputable sign of physics beyond the Standard Model. We derive constraints on the CP-violating Higgs-boson couplings to top and bottom quarks as well as to tau leptons from low-energy bounds on electric dipole moments, resumming large logarithms when necessary. The present and future projections of the sensitivities and comparisons with the LHC constraints are provided. Non-trivial constraints are possible in the future, even if the Higgs boson only couples to the third-generation fermions.

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arXiv2013

The ultimate theoretical error on gamma from B -> D K decays

The angle gamma of the standard CKM unitarity triangle can be determined from B -> D K decays with a very small irreducible theoretical error, which is only due to second-order electroweak corrections. We study these contributions and estimate that their impact on the gamma determination is to introduce a shift |delta gamma| <~ O(10^-7), well below any present or planned future experiment.

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arXiv2013

From gamma ray line signals of dark matter to the LHC

We explore the relationship between astrophysical gamma-ray signals and LHC signatures for a class of phenomenologically successful secluded dark matter models, motivated by recent evidence for a ~130 GeV gamma-ray line. We consider in detail scenarios in which interactions between the dark sector and the standard model are mediated by a vev-less scalar field ϕ, transforming as an N-plet (N > 3) under SU(2)_L. Since some of the component fields of ϕcarry large electric charges, loop induced dark matter annihilation to γγand γZ can be enhanced without the need for non-perturbatively large couplings, and without overproduction of continuum gamma-rays from other final states. We discuss prospects for other experimental tests, including dark matter-nucleon scattering and production of ϕat the LHC, where future searches for anomalous charged tracks may be sensitive. The first LHC hints could come from the Higgs sector, where loop corrections involving ϕlead to significantly modified h to γγand h to γZ branching ratios.

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arXiv2013

Halo-independent methods for inelastic dark matter scattering

We present halo-independent methods to analyze the results of dark matter direct detection experiments assuming inelastic scattering. We focus on the annual modulation signal reported by DAMA/LIBRA and present three different halo-independent tests. First, we compare it to the upper limit on the unmodulated rate from XENON100 using (a) the trivial requirement that the amplitude of the annual modulation has to be smaller than the bound on the unmodulated rate, and (b) a bound on the annual modulation amplitude based on an expansion in the Earth's velocity. The third test uses the special predictions of the signal shape for inelastic scattering and allows for an internal consistency check of the data without referring to any astrophysics. We conclude that a strong conflict between DAMA/LIBRA and XENON100 in the framework of spin-independent inelastic scattering can be established independently of the local properties of the dark matter halo.

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arXiv2013

Flavoured Naturalness

We show that a large mixing between the right-handed charm and top squarks (i) is allowed by low-energy flavour constraints; (ii) reduces the experimental bound on the stop mass; (iii) has a mild, but beneficial, effect on fine-tuning; (iv) leads to interesting signatures at the LHC not presently investigated by experiments. We estimate the current bound on the stop mass, in presence of flavour mixing, and discuss the new collider signatures. The signal in the t anti-c (c anti-t) + missing E_T channel is large enough that it can be immediately searched for experimentally, while the signature with same-sign tops and missing E_T requires a luminosity upgrade of the LHC.

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arXiv2013

How to test for mass degenerate Higgs resonances

The Higgs-like signal observed at the LHC could be due to several mass degenerate resonances. We show that the number of resonances is related to the rank of a "production and decay" matrix, $R_{if}$. Each entry in this matrix contains the observed rate in a particular production mode $i$ and final state $f$. In the case of $N$ non-interfering resonances, the rank of $R$ is, at most, $N$. If interference plays a role, the maximum rank is $N^2$ or in the CP limit $N(N+1)/2$. As an illustration we use the present experimental data to constrain the rank of the corresponding matrix. We estimate the LHC reach of probing two and three resonances under various speculations on future measurements and uncertainties.

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arXiv2013

Implications of lepton flavor universality violations in B decays

Present measurements of b->c tau nu and b->u tau nu transitions differ from the standard model predictions of lepton flavor universality by almost 4sigma. We examine new physics interpretations of this anomaly. An effective field theory analysis shows that minimal flavor violating models are not preferred as an explanation, but are also not yet excluded. Allowing for general flavor violation, right-right vector and right-left scalar quark currents are identified as viable candidates. We discuss explicit examples of two Higgs doublet models, leptoquarks as well as quark and lepton compositeness. Finally, implications for LHC searches and future measurements at the (super)B- factories are presented.

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arXiv2012

B^\pm -> D K^\pm with direct CP violation in charm

We investigate the implications of direct CP violation (CPV) on the determination of the unitarity triangle angle γ from B -> DK decays. We show that γ can still be extracted even with the inclusion of direct CPV in charm if (i) at least one of the D decays has negligible CP violation; and (ii) data from charm factory at threshold are used. If approximate expressions without including direct CP violation in charm are used, this can result in a shift in γ that is O(r_D/r_B). It is modest for B -> DK but can be O(1) for B -> Dπ. We illustrate the size of the shift on an example of Gronau-London-Wyler method.

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arXiv2012

Forward Tevatron Tops and Backward LHC Tops with Associates

The anomalous forward-backward asymmetry (A_FB) in t tbar production at the Tevatron is in apparent contradiction with the t tbar charge asymmetry (A_C) measurements at the LHC, which agree well with the standard model predictions. We argue that associated production of a state with [u tbar] flavor quantum numbers can lead to a sizable negative contribution to A_C. Exchange of such a resonance in the t-channel would lead to positive contributions to A_FB and A_C, as has been extensively discussed in the literature. Given the additional negative A_C contribution, both the Tevatron and LHC data can be naturally accommodated within this framework. A simple realization of this setup is the well known example of a Z' with flavor off-diagonal up-top couplings. We provide a detailed study of this model, demonstrating that it indeed reproduces the t tbar asymmetry data, and is compatible with other constraints, e.g. t+jet resonance searches, t tbar inclusive jet multiplicities, and atomic parity violation.

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arXiv2012

Higgs After the Discovery: A Status Report

Recently, the ATLAS and CMS collaborations have announced the discovery of a 125 GeV particle, commensurable with the Higgs boson. We analyze the 2011 and 2012 LHC and Tevatron Higgs data in the context of simplified new physics models, paying close attention to models which can enhance the diphoton rate and allow for a natural weak-scale theory. Combining the available LHC and Tevatron data in the ZZ* 4-lepton, WW* 2-lepton, diphoton, and b-bbar channels, we derive constraints on the effective low-energy theory of the Higgs boson. We map several simplified scenarios to the effective theory, capturing numerous new physics models such as supersymmetry, composite Higgs, dilaton. We further study models with extended Higgs sectors which can naturally enhance the diphoton rate. We find that the current Higgs data are consistent with the Standard Model Higgs boson and, consequently, the parameter space in all models which go beyond the Standard Model is highly constrained.

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arXiv2012

Higgs portal, fermionic dark matter, and a Standard Model like Higgs at 125 GeV

We show that fermionic dark matter (DM) which communicates with the Standard Model (SM) via the Higgs portal is a viable scenario, even if a SM-like Higgs is found at around 125 GeV. Using effective field theory we show that for DM with a mass in the range from about 60 GeV to 2 TeV the Higgs portal needs to be parity violating in order to be in agreement with direct detection searches. For parity conserving interactions we identify two distinct options that remain viable: a resonant Higgs portal, and an indirect Higgs portal. We illustrate both possibilities using a simple renormalizable toy model.

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arXiv2012

Flipping t tbar asymmetries at the Tevatron and the LHC

We show that the charge asymmetry in t tbar production at the LHC, A_C, and the forward-backward asymmetry at the Tevatron, A_FB, are in general not tightly correlated. They can even have opposite signs, if the underlying new physics (NP) model is general enough. We demonstrate this using two examples of NP: a light axigluon, and a vector that is a color octet and electroweak triplet. The small value of A_C measured at the LHC is thus shown not to exclude a NP interpretation of the anomalously large A_FB at the Tevatron. We identify two observables where significant NP effects are still expected at the Tevatron and the LHC, the b bbar production forward-backward asymmetry and spin polarizations of the pair-produced tops and anti-tops.

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arXiv2012

Astrophysics independent bounds on the annual modulation of dark matter signals

We show how constraints on the time integrated event rate from a given dark matter (DM) direct detection experiment can be used to set a stringent constraint on the amplitude of the annual modulation signal in another experiment. The method requires only very mild assumptions about the properties of the local DM distribution: that it is temporally stable on the scale of months and spatially homogeneous on the ecliptic. We apply the method to the annual modulation signal in DAMA/LIBRA, which we compare to the bounds derived from the constraints on the time-averaged rates from XENON10, XENON100, CDMS and SIMPLE. Assuming a DM mass of 10 GeV, we show that a DM interpretation of the DAMA/LIBRA signal is excluded at 6.3sigma (4.6sigma) for isospin conserving (violating) spin-independent interactions, and at 4.9sigma for spin-dependent interactions on protons.

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arXiv2012

Testing for new physics in singly Cabibbo suppressed D decays

We devise tests for a new physics origin of the recently measured direct CP violation in singly Cabibbo suppressed D decays. The tests take the form of sum rules for the CP asymmetries in various D decays. They are based on the fact that within the standard model CP violation arises from interference of the dominant tree amplitudes with the Delta I=1/2 penguin amplitudes. The sum rules would be violated if the observed CP violation is due to new physics contributions to the effective weak Hamiltonian that change isospin by Delta I=3/2.

hep-ph↗

arXiv2012

A consistent picture for large penguins in D -> pi+ pi-, K+ K-

A long-standing puzzle in charm physics is the large difference between the D0 -> K+ K- and D0 -> pi+ pi- decay rates. Recently, the LHCb and CDF collaborations reported a surprisingly large difference between the direct CP asymmetries, Delta A_CP, in these two modes. We show that the two puzzles are naturally related in the Standard Model via s- and d-quark "penguin contractions". Their sum gives rise to Delta A_CP, while their difference contributes to the two branching ratios with opposite sign. Assuming nominal SU(3) breaking, a U-spin fit to the D0 -> K+ pi-, pi+ K-, pi+ pi-, K+ K- decay rates yields large penguin contractions that naturally explain Delta A_CP. Expectations for the individual CP asymmetries are also discussed.

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arXiv2012

On the annual modulation signal in dark matter direct detection

We derive constraints on the annual modulation signal in Dark Matter (DM) direct detection experiments in terms of the unmodulated event rate. A general bound independent of the details of DM distribution follows from the assumption that the motion of the earth around the sun is the only source of time variation. The bound is valid for a very general class of particle physics models and also holds in the presence of an unknown unmodulated background. More stringent bounds are obtained, if modest assumptions on symmetry properties of the DM halo are adopted. We illustrate the bounds by applying them to the annual modulation signals reported by the DAMA and CoGeNT experiments in the framework of spin-independent elastic scattering. While the DAMA signal satisfies our bounds, severe restrictions on the DM mass can be set for CoGeNT.

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arXiv2011

Light Dark Matter in the light of CRESST-II

Recently the CRESST collaboration has published the long anticipated results of their direct Dark Matter (DM) detection experiment with a CaWO_4 target. The number of observed events exceeds known backgrounds at more than 4 sigma significance, and this excess could potentially be due to DM scattering. We confront this interpretation with null results from other direct detection experiments for a number of theoretical models, and find that consistency is achieved in non-minimal models such as inelastic DM and isospin-violating DM. In both cases mild tension with constraints remain. The CRESST data can, however, not be reconciled with the null results and with the positive signals from DAMA and CoGeNT simultaneously in any of the models we study.

hep-ph↗

arXiv2011

Flavor Symmetric Sectors and Collider Physics

We discuss the phenomenology of effective field theories with new scalar or vector representations of the Standard Model quark flavor symmetry group, allowing for large flavor breaking involving the third generation. Such field content can have a relatively low mass scale \lesssim TeV and O(1) couplings to quarks, while being naturally consistent with both flavor violating and flavor diagonal constraints. These theories therefore have the potential for early discovery at LHC, and provide a flavor safe "tool box" for addressing anomalies at colliders and low energy experiments. We catalogue the possible flavor symmetric representations, and consider applications to the anomalous Tevatron t-tbar forward backward asymmetry and B_s mixing measurements, individually or concurrently. Collider signatures and constraints on flavor symmetric models are also studied more generally. In our examination of the t-tbar forward backward asymmetry we determine model independent acceptance corrections appropriate for comparing against CDF data that can be applied to any model seeking to explain the t-tbar forward backward asymmetry.

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