Light Scalars Research Articles

Next-to-minimalR-symmetric model: Dirac gaugino, Higgs mass and invisible width

We study a singlet extension of the minimal $U(1)_R$ symmetric model, which shares nice properties of Dirac gauginos and $R$-symmetric Higgs sector. At the same time, a superpotential coupling of $R$-charged singlet to the Higgs doublets can give a substantial contribution to the Higgs boson mass. We show that the 125 GeV Higgs boson is consistent with perturbative unification, even if the SUSY scale is as low as 1 TeV and if the $D$-term Higgs potential is suppressed as is often the case in Dirac gauginos. The model also contains a light scalar and fermion, pseudo-moduli and pseudo-Goldstino: The former gets a mass mainly from SUSY breaking soft terms, in addition to a small explicit $R$-symmetry breaking for the latter. We examine how the Higgs mass and width are affected by these light degrees of freedom. Specifically we find thatdepending on parameters of $R$-charged Higgses, the pseudo-moduli lighter than a half of the SM-Higgs boson mass is still allowed by the constraints from invisible decays of the $Z$ and Higgs bosons. We also find that such a light scalar can reduce the Higgs boson mass, at most by a few percents.

Enhanced sensitivity of the Z-scan technique on saturable absorbers using radially polarized beams

We develop the Z-scan technique on a saturable absorber under the excitation of radially polarized beams. It is shown that the sensitivity of the Z-scan measurements on a saturable absorber using radially polarized beams has the great improvement compared with those using the scalar light beams such as Gaussian beams, Laguerre-Gaussian beams, and top-hat beams. As the experimental evidence, we investigate the saturable absorption properties of layered WS2 nanosheets in aqueous suspension by performing the radially polarized-beam Z-scan measurements with femtosecond laser pulses in the near infrared region.

Search for mirror quarks at the LHC

Observation of non-zero neutrino masses at a scale $\sim 10^{-1} - 10^{-2}$ eV is a major problem in the otherwise highly successful Standard Model. The most elegant mechanism to explain such tiny neutrino masses is the seesaw mechanism with right handed neutrinos. However, the required seesaw scale is so high, $\sim 10^{14}$ GeV, it will not have any collider implications. Recently, an explicit model has been constructed to realize the seesaw mechanism with the right handed neutrinos at the electroweak scale. The model has a mirror symmetry having both the left and right lepton and quark doublets and singlets for the same $SU(2)_W $ gauge symmetry. Additional Higgs multiplets have been introduced to realize this scenario. It turns out that these extra Higgs fields also help to satisfy the precision electroweak tests, and other observables. Because the scale of the symmetry breaking is electroweak, both the mirror quark and mirror leptons have masses in the electroweak scale in the range $ \sim 150 - 800 $ GeV. The mirror quarks / leptons decay to ordinary quarks /leptons plus very light neutral scalars. In this work, we calculate the final state signals arising from the pair productions of these mirror quarks and their subsequent decays. We find that these signals are well observable over the Standard Model background for $13$ TeV LHC. Depending on the associated Yukawa couplings, these decays can also give rise displaced vertices with long decay length, very different from the usual displaced vertices associated with b decays.

Sound of Dark Matter: Searching for Light Scalars with Resonant-Mass Detectors.

The fine-structure constant and the electron mass in string theory are determined by the values of scalar fields called moduli. If the dark matter takes on the form of such a light modulus, it oscillates with a frequency equal to its mass and an amplitude determined by the local dark-matter density. This translates into an oscillation of the size of a solid that can be observed by resonant-mass antennas. Existing and planned experiments, combined with a dedicated resonant-mass detector proposed in this Letter, can probe dark-matter moduli with frequencies between 1 kHz and 1 GHz, with much better sensitivity than searches for fifth forces.

SHiP: a new multipurpose beam-dump experiment at the SPS

SHiP is an experiment to look for very weakly interacting particles at a new to be constructed beam-dump facility at the CERN SPS. The SHiP Technical Proposal has been submitted to the CERN SPS Committee in April 2015. The 400 GeV/c proton beam extracted from the SPS will be dumped on a heavy target with the aim of integrat- ing 2× 10 20 proton on target in five years. A detector located downstream of the targe t, based on a long vacuum tank followed by a spectrometer and particle identifi cation de- tectors, will allow probing a variety of models with light long-lived exotic partic les and masses below a few GeV/c 2 . The main focus will be the physics of the so-called Hid- den Portals, i.e. search for Dark Photons, Light scalars and pseudo-scalars, and Heavy Neutral Leptons (HNL). The sensitivity to HNL will allow for the first time to pr obe, in the mass range between the kaon and the charm meson mass, a coupling range for which Baryogenesis and active neutrino masses could also be explained. Integrated in SHiP is an Emulsion Cloud Chamber, already used in the OPERA experiment, which will allow to study active neutrino cross-sections and angular distributions. In par ticular SHiP can distinguish betweeno? and ¯ o?, and their deep inelastic scattering cross sections will be measured with statistics three orders of magnitude larger than currently available.

The SM extensions with additional light scalar singlet, nonrenor-malizable Yukawa interactions and (g− 2)μ

We consider the SM extension with additional light real singlet scalar, right-handed neutrino and nonrenormalizable Yukawa interaction for the first two generations. We show that the proposed model can explain the observed $(g - 2)$ muon anomaly. Phenomenological consequences as flavour violating decays $\tau \rightarrow \mu\mu\mu, \mu \mu e, \mu e e $ are briefly discussed. We also propose the $U_R(1)$ gauge generalization of the SM with complex scalar singlet and nonzero right-handed charges for the first two generations.

Status and prospects of the nMSSM after LHC Run-1

The new minimal supersymmetric standard model (nMSSM), a variant of the general next to minimal supersymmetric standard model (NMSSM) without $Z_3$ symmetry, features a naturally light singlino with a mass below 75 GeV. In light of the new constraints from LHC Run-1 on the Higgs couplings, sparticles searches and flavour observables, we define the parameter space of the model which is compatible with both collider and dark matter (DM) properties. Among the regions compatible with these constraints, implemented through NMSSMTools, SModelS and MadAnalysis 5, only one with a singlino lightest supersymmetric particle (LSP) with a mass around 5 GeV can explain all the DM abundance of the universe, while heavier mixed singlinos can only form one of the DM components. Typical collider signatures for each region of the parameter space are investigated. In particular, the decay of the 125 GeV Higgs into light scalars and/or pseudoscalars and the decay of the heavy Higgs into charginos and neutralinos, provide distinctive signatures of the model. Moreover, the sfermion decays usually proceed through heavier neutralinos rather than directly into the LSP, as the couplings to the singlino are suppressed. We also show that direct detection searches are complementary to collider ones, and that a future ton-scale detector could completely probe the region of parameter space with a LSP mass around 65 GeV.

Search for a very light NMSSM Higgs boson produced in decays of the 125 GeV scalar boson and decaying into τ leptons in pp collisions at s = 8 $$ \sqrt{s}=8 $$ TeV

A search for a very light Higgs boson decaying into a pair of tau leptons is presented within the framework of the next-to-minimal supersymmetric standard model. This search is based on a data set corresponding to an integrated luminosity of 19.7 inverse femtobarns of proton-proton collisions collected by the CMS experiment at a centre-of-mass energy of 8 TeV. The signal is defined by the production of either of the two lightest scalars, h[1] or h[2], via gluon-gluon fusion and subsequent decay into a pair of the lightest Higgs bosons, a[1] or h[1]. The h[1] or h[2] boson is identified with the observed state at a mass of 125 GeV. The analysis searches for decays of the a[1] (h[1]) states into pairs of tau leptons and covers a mass range for the a[1] (h[1]) boson of 4 to 8 GeV. The search reveals no significant excess in data above standard model background expectations, and an upper limit is set on the signal production cross section times branching fraction as a function of the a[1] (h[1]) boson mass. The 95% confidence level limit ranges from 4.5 pb at m(a[1]) (m(h[1])) = 8 GeV to 10.3 pb at m(a[1]) (m(h[1])) = 5 GeV.

Probing MeV to 90 GeV axion-like particles with LEP and LHC

Axion-like particles (ALPs), relatively light (pseudo-)scalars coupled to two gauge bosons, are a common feature of many extensions of the Standard Model. Up to now there has been a gap in the sensitivity to such particles in the MeV to 10 GeV range. In this note we show that LEP data on Z→γγ decays provides significant constraints in this range (and indeed up to the Z-mass). We also discuss the sensitivities of LHC and future colliders. Particularly the LHC shows promising sensitivity in searching for a pseudo-scalar with 4≲ma≲60 GeV in the channel pp→3γ with m3γ≈mZ.

Probing a light CP-odd scalar in di-top-associated production at the LHC

CP-odd scalars are an integral part of many extensions of the Standard Model. Recently, electroweak-scale pseudoscalars have received increased attention in explaining the diffuse gamma-ray excess from the Galactic Centre. Elusive due to absence of direct couplings to gauge bosons, these particles receive only weak constraints from direct searches at LEP or searches performed during the first LHC runs. We investigate the LHC’s sensitivity in probing a CP-odd scalar in the mass range $$20 \le m_A \le 100$$ GeV via di-top-associated production using jet-substructure-based reconstruction techniques. We parameterise the scalar’s interactions using a simplified model approach and relate the obtained upper limits to couplings within type-I and type-II 2HDMs as well as the NMSSM. We find that in di-top-associated production, experiments at the LHC can set tight limits on CP-odd scalars that fit the Galactic Centre excess. However, direct sensitivity to light CP-odd scalars from the NMSSM remains challenging.

Early universe cosmology, effective supergravity, and invariants of algebraic forms

The presence of light scalars can have profound effects on early universe cosmology, influencing its thermal history as well as paradigms like inflation and baryogenesis. Effective supergravity provides a framework to make quantifiable, model-independent studies of these effects. The Riemanian curvature of the Kahler manifold spanned by scalars belonging to chiral superfields, evaluated along supersymmetry breaking directions, provides an order parameter (in the sense that it must necessarily take certain values) for phenomena as diverse as slow roll modular inflation, non-thermal cosmological histories, and the viability of Affleck-Dine baryogenesis. Within certain classes of UV completions, the order parameter for theories with $n$ scalar moduli is conjectured to be related to invariants of $n$-ary cubic forms (for example, for models with three moduli, the order parameter is given by the ring of invariants spanned by the Aronhold invariants). Within these completions, and under the caveats spelled out, this may provide an avenue to obtain necessary conditions for the above phenomena that are in principle calculable given nothing but the intersection numbers of a Calabi-Yau compactification geometry. As an additional result, abstract relations between holomorphic sectional and bisectional curvatures are utilized to constrain Affleck-Dine baryogenesis on a wide class of Kahler geometries.

B-factory searches for light scalars and other new states

New Higgs scalars with masses up to 10 GeV are predicted in models such as the NMSSM, and in scenarios with hidden sectors that couple weakly to the Standard Model. Searches at B factories have resulted in tight constraints on such models. We review the recent searches and new results, and discuss the future outlook for this physics.

Dark matter from the supersymmetric custodial triplet model

The Supersymmetric Custodial Triplet Model (SCTM) adds to the particle content of the MSSM three $SU(2)_L$ triplet chiral superfields with hypercharge $Y=(0,\pm1)$. At the superpotential level the model respects a global $SU(2)_L \otimes SU(2)_R$ symmetry only broken by the Yukawa interactions. The pattern of vacuum expectation values of the neutral doublet and triplet scalar fields depends on the symmetry pattern of the Higgs soft breaking masses. We study the cases where this symmetry is maintained in the Higgs sector, and when it is broken only by the two doublets attaining different vacuum expectation values. In the former case, the symmetry is spontaneously broken down to the vectorial subgroup $SU(2)_V$ and the $\rho$ parameter is protected by the custodial symmetry. However in both situations the $\rho$ parameter is protected at tree level, allowing for light triplet scalars with large vacuum expectation values. We find that over a large range of parameter space, a light neutralino can supply the correct relic abundance of dark matter either through resonant s-channel triplet scalar funnels or well tempering of the Bino with the triplet fermions. Direct detection experiments have trouble probing these model points because the custodial symmetry suppresses the coupling of the neutralino and the $Z$ and a small Higgsino component of the neutralino suppresses the coupling with the Higgs. Likewise the annihilation cross sections for indirect detection lie below the Fermi-LAT upper bounds for the different channels.

Inhomogeneous broadening of optical transitions of 87Rb atoms in an optical nanofiber trap

We experimentally demonstrate optical trapping of atoms using a two-color evanescent field around an optical nanofiber. In our trapping geometry, a blue-detuned traveling wave whose polarization is nearly parallel to the polarization of a red-detuned standing wave produces significant vector light shifts that lead to broadening of the absorption profile of a near-resonant beam at the trapping site. A model that includes scalar, vector, and tensor light shifts of the probe transition - from the trapping beams, weighted by the temperature-dependent position of the atoms in the trap, qualitatively describes the observed asymmetric profile and explains differences with previous experiments that used Cs atoms. The model provides a consistent way to extract the number of atoms in the trap.

Low-energy phenomenology of trinification: An effective left-right-symmetric model

The trinification model is an interesting extension of the Standard Model (SM) based on the gauge group $SU(3)_C\times SU(3)_L\times SU(3)_R$. We study its low-energy phenomenology by constructing a low-energy effective field theory, thereby reducing the number of particles and free parameters that need to be studied. The resulting model predicts that several new scalar particles have masses in the $\mathcal{O}\left(100\text{ GeV}\right)$ range. We study a few of the interesting phenomenological scenarios, such as the presence of a light fermiophobic scalar in addition to a SM-like Higgs, or a degenerate (twin) Higgs state at 126 GeV. We point out regions of the parameter space that lead to measurable deviations from SM predictions of the Higgs couplings. Hence the trinification model awaits crucial tests at the Large Hadron Collider in the coming years.

Hunting physics beyond the standard model with unusualW±andZdecays

Nonstandard on-shell decays of ${W}^{\ifmmode\pm\else\textpm\fi{}}$ and $Z$ bosons are possible within the framework of extended supersymmetric models, i.e., with singlet states and/or new couplings compared to the minimal supersymmetric standard model. These modes are typically encountered in regions of the parameter space with light singlet-like scalars, pseudoscalars, and neutralinos. In this letter we emphasize how these states can lead to novel signals at colliders from $Z$- or ${W}^{\ifmmode\pm\else\textpm\fi{}}$-boson decays with prompt or displaced multileptons/tau jets/jets/photons in the final states. These new modes would give distinct evidence of new physics even when direct searches remain unsuccessful. We discuss the possibilities of probing these new signals using the existing LHC run-I data set. We also address the same in the context of the LHC run-II, as well as for the future colliders. We exemplify our observations with the ``$\ensuremath{\mu}$ from $\ensuremath{\nu}$'' supersymmetric standard model, where three generations of right-handed neutrino superfields are used to solve shortcomings of the minimal supersymmetric standard model. We also extend our discussion for other variants of supersymmetric models that can accommodate similar signatures.

Probing the μνSSM with light scalars, pseudoscalars and neutralinos from the decay of a SM-like Higgs boson at the LHC

The "$\mu$ from $\nu$" supersymmetric standard model ($\mu\nu$SSM) can accommodate the newly discovered Higgs-like scalar boson with a mass around 125 GeV. This model provides a solution to the $\mu$-problem and simultaneously reproduces correct neutrino physics by the simple use of right-handed neutrino superfields. These new superfields together with the introduced $R$-parity violation can produce novel and characteristic signatures of the $\mu\nu$SSM at the LHC. We explore the signatures produced through two-body Higgs decays into the new states, provided that these states lie below in the mass spectrum. For example, a pair produced light neutralinos depending on the associated decay length can give rise to displaced multi-leptons/taus/jets/photons with small/moderate missing transverse energy. In the same spirit, a Higgs-like scalar decaying to a pair of scalars/pseudoscalars can produce final states with prompt multi-leptons/taus/jets/photons.

The double-dark portal

In most models of the dark sector, dark matter is charged under some new symmetry to make it stable. We explore the possibility that not just dark matter, but also the force carrier connecting it to the visible sector is charged under this symmetry. This dark mediator then acts as a Double-Dark Portal. We realize this setup in the \emph{dark mediator Dark matter} model (dmDM), featuring a fermionic DM candidate $\chi$ with Yukawa couplings to light scalars $\phi_i$. The scalars couple to SM quarks via the operator $\bar q q \phi_i^* \phi_j/\Lambda_{ij}$. This can lead to large direct detection signals via the $2\rightarrow3$ process $\chi N \rightarrow \chi N \phi$ if one of the scalars has mass $ \lesssim 10$ keV. For dark matter Yukawa couplings $y_\chi \sim 10^{-3} - 10^{-2}$, dmDM features a thermal relic dark matter candidate while also implementing the SIDM scenario for ameliorating inconsistencies between dwarf galaxy simulations and observations. We undertake the first systematic survey of constraints on light scalars coupled to the SM via the above operator. The strongest constraints are derived from a detailed examination of the light mediator's effects on stellar astrophysics. LHC experiments and cosmological considerations also yield important bounds. Observations of neutron star cooling exclude the minimal model with one dark mediator, but a scenario with two dark mediators remains viable and can give strong direct detection signals. We explore the direct detection consequences of this scenario and find that a heavy $\mathcal{O}(100)$ GeV dmDM candidate fakes different $\mathcal{O}(10)$ GeV WIMPs at different experiments. Large regions of dmDM parameter space are accessible above the irreducible neutrino background.

Minimal model of Majoronic dark radiation and dark matter

We extend the singlet Majoron model of dark radiation by adding another singlet scalar of unit lepton charge. The spontaneous breaking of global $U(1{)}_{L}$ connects dark radiation with neutrino mass generation via the type-I seesaw mechanism. The model naturally has a stable scalar dark matter field. It also predicts the existence of a light scalar of mass less than 1 GeV that mixes with the Standard Model Higgs boson. We perform a numerical analysis of the parameters of the model by imposing constraints from giving correct relic abundance and satisfying bounds from direct dark matter detection, rare decays of the $B$ meson, and invisible width of the Higgs boson. The viability of the model in accommodating the gamma rays from the Galactic center is discussed as well. The model gives rise to new rare Higgs boson decays such as four-muon final states with displaced vertices. Another unique signal is two muons and missing energy recoil against the muon pair. Our result also shows that such a bridge between dark radiation and the seesaw mechanism will put the seesaw scale in the range of 1--100 TeV.

Neutrino mass generation and singly charged leptonic exotics in WW events

Current measurement of leptonic WW is significantly higher than the standard model prediction which may accommodate new physics signal that mimics the leptonic decaying W. We investigate a TeV neutrino mass generation model that predicts singly charged leptonic exotics. The collider signature of this model may mimic the leptonic WW search and evade all other searches. With introduction of new SU(2)L doublet leptons, singly charged exotic leptons L± decay into L±→ℓ±ϕ where ϕ is a light singlet scalar of O(MeV) that decays into neutrinos. Drell–Yan production of L+L−→ℓ+ℓ−+E̸T fits leptonic WW searches and L±L0→ℓ±+E̸T is completely buried in SM background. In the case of direct lepton from L-decay instead of secondary decay from leptonic τ±, we find the lower mass bound as 125 GeV of such exotic leptons that can be accommodated by the current measurements of WW searches at the LHC. To derive the upper bound, we employ both heavy Higgs boson search of di-lepton plus E̸T final state and leptonic W′ search of single lepton plus E̸T. Even though heavy Higgs is excluded between 260 and 640 GeV, we find LHC data can still accommodate L between 150 and 300 GeV after giving up the ηℓℓ cut. Using the single W′ search bound, we can obtain an approximate upper bound as 300 GeV.