Search

The present study aims to unveil a scenario with a non-minimal secluded dark sector (DS) in an effective field theory (EFT) framework. To explore this, we have examined a suitable extension of the type-X Two Higgs Doublet Model (2HDM) as a potential origin for the secluded DS. The DS comprises a dark matter (DM) candidate and a mediator particle `$a$' and possesses some non-minimal characteristics. It becomes non-thermally populated through diverse dim-6 four-Fermi operators, effectively generated by integrating out the heavier Higgs particles. The analysis further focuses on the consequences of the collision processes $\textit{DM}+ a \leftrightarrow a + a$ and $\textit{DM}+ \textit{DM} \leftrightarrow a + a$ occurring within the DS. We have investigated the significance of employing an EFT approach in tracking the temperature evolution of the DS. Within the present framework, the observed relic abundance of the DM can be realized through both dark freeze-out and freeze-in mechanisms. Further, we have delineated the permissible ranges of the relevant parameters, viz., the DM mass ($m_\chi \gtrsim 20 \, \text{GeV}$), the portal coupling ($C_\tau \lesssim 10^{-14}\, \text{GeV}^{-2}$), and the DS coupling ($\lambda \lesssim 10^{-6} \,\text{GeV}^{-2}$) by taking into account the perturbativity of the involved couplings while reproducing the observed DM relic and complying with the bounds from a successful Big Bang Nucleosynthesis (BBN) and $\gamma$-ray searches., Comment: 30 pages, LaTeX, 7 figures, 3 tables, Significant changes in the text. Conclusion partially changed

We study the prospects of a simultaneous hunt at the Large Hadron Collider (LHC) of relatively light electroweakinos and a singlet-like scalar of the $Z_3$-symmetric Next-to-Minimal Supersymmetric Standard Model ($Z_3$-NMSSM) in the cascade decays of not so heavy ($\lesssim 1.5$ TeV) top squarks that are produced in pairs at the LHC which characteristically involve the singlet-like states. We work in a scenario where the lightest (next-to-lightest) SUSY particle is bino (singlino)-like with a mass below 100 GeV ($\gtrsim 100$ GeV), whereas a pair of immediately heavier neutralinos and the lighter chargino are higgsino-like with masses in the range $\sim 500$ GeV -- 1 TeV. Further, the singlet-like scalar present in the spectrum provides a funnel for a rapid enough mutual annihilation of the LSP thus making the latter meet the experimental upper bound on its relic abundance. The scenario is motivated by its ability to offer a bino-like dark matter with such a mass unlike what is now disfavored in the MSSM while avoiding the stringent lower bounds from the LHC experiments on the masses of these involved particles and still remaining reasonably `natural'. We find that while a usual cut-based analysis (CBA) on LHC data worth 300 $\text{fb}^{-1}$ would be unable to discover such excitations, a multivariate analysis (MVA) can be reasonably sensitive to higgsino-like electroweakinos having masses $\gtrsim 650$ GeV when the lighter top squark has a mass $\gtrsim 1$ TeV. On the other hand, with 3000 $\text{fb}^{-1}$ of data these masses become accessible in a CBA while even an MVA on such a data set is unlikely to find these electroweakinos with masses around 1 TeV when the mass of the lighter top squark hits $\sim 1.5$ TeV., Comment: 38 pages, 6 figures, 6 tables, Matched with the JHEP published version

We study in detail the viability and the patterns of a strong first-order electroweak phase transition as a prerequisite to electroweak baryogenesis in the framework of $Z_3$-invariant Next-to-Minimal Supersymmetric Standard Model (NMSSM), in the light of recent experimental results from the Higgs sector, dark matter (DM) searches and those from the searches of the lighter chargino and neutralinos at the Large Hadron Collider (LHC). For the latter, we undertake thorough recasts of the relevant, recent LHC analyses. With the help of a few benchmark scenarios, we demonstrate that while the LHC has started to eliminate regions of the parameter space with relatively small $\mu_\mathrm{eff}$, that favors the coveted strong first-order phase transition, rather steadily, there remains phenomenologically much involved and compatible regions of the same which are yet not sensitive to the current LHC analyses. It is further noted that such a region could also be compatible with all pertinent theoretical and experimental constraints. We then proceed to analyze the prospects of detecting the stochastic gravitational waves, which are expected to arise from such a phase transition, at various future/proposed experiments, within the mentioned theoretical framework and find them to be somewhat ambitious under the currently projected sensitivities of those experiments., Comment: 52 pages, 3 figures, 6 tables. published version, references added

In the NonHolomorphic Supersymmetric Standard Model (NHSSM), the Yukawa couplings of the bottom quark ($y_b$) and the tau lepton ($y_{\tau}$) might receive substantial supersymmetric (SUSY) radiative corrections which have prominent dependencies on the NHSSM-specific trilinear soft parameters, $A_b^\prime$ and $A_{\tau}^\prime$, respectively, in addition to their well-known dependence on $\tan\beta$ as is already present in the Minimal SUSY Standard Model (MSSM). We study to what extent these could affect the production cross sections of the heavy Higgs bosons ($H$ and $A$) in association with a pair of $b$-quarks and their decay branching ratios, in particular, to a $\tau\bar{\tau}$ pair and compare them with those obtained in the MSSM. Requiring compliance with the recently observed upper bounds on the product of their total cross-section and the branching ratio to $\tau\bar{\tau}$ at the 13 TeV run of the Large Hadron Collider (LHC), with data worth 139 fb$^{-1}$, results in an altered exclusion region in the customary $m_A-\tan\beta$ plane in the framework of the NHSSM when compared to what is derived by the LHC experiments within an MSSM setup. Such alterations are estimated to be pronounced only for large $\tan\beta$ ($\geq 40$) and for large, negative $A_b^\prime$ when one finds a reinforced exclusion of the $m_A-\tan\beta$ plane with an excluded $m_A$ value larger by $\approx 200$ GeV, compared to the MSSM case, at $\tan\beta=60$. On the other hand, the maximum relaxation in $m_A$, for a similarly large but positive $A_b^\prime$, barely exceeds $\approx 100$ GeV as a result of complementary variations in production cross-sections and decay branching fractions of the heavy, neutral Higgs bosons., Comment: 24 pages, 7 figures, a few modifications in the text, equations 2.4 and 2.6 updated, conclusions unchanged

A highly bino-like Dark Matter (DM), which is the Lightest Supersymmetric Particle (LSP), could be motivated by the stringent upper bounds on the DM direct detection rates. This is especially so when its mass is around or below 100 GeV for which such a bound tends to get most severe. Requiring not so large a higgsino mass parameter, that would render the scenario reasonably natural, prompts such a bino-like state to be relatively light. In the Minimal Supersymmetric Standard Model (MSSM), in the absence of comparably light scalars, such an excitation, if it has to be a thermal relic, is unable to meet the stringent experimental upper bound on its abundance unless its self-annihilation hits a funnel involving either the $Z$-boson or the Standard Model (SM)-like Higgs boson. We demonstrate that, in such a realistic situation, a highly bino-like DM of the popular $Z_3$-symmetric Next-to-Minimal Supersymmetric Standard Model (NMSSM) is viable over an extended range of its mass, from our targeted maximum in the vicinity of the mass of the top quark down to about 30 GeV. This is facilitated by the presence of comparably light singlet-like states that could serve as funnel (scalars) and/or coannihilating (singlino) states even as the bino-like LSP receives a minimal (but optimal) tempering triggered by suitably light higgsino states that, in the first place, evade stringent lower bounds on their masses that can be derived from the Large Hadron Collider (LHC) experiments only in the presence of a lighter singlino-like state. An involved set of blind spot conditions is derived for the DM direct detection rates by considering for the very first time the augmented system of neutralinos comprising of the bino, the higgsinos and the singlino which highlights the important roles played by the NMSSM parameters $\lambda$ and $\tan\beta$ in delivering a richer phenomenology., Comment: 70 pages, 16 figures and 3 tables

Inspired by the fact that relatively small values of the effective higgsino mass parameter of the $Z_3$-symmetric Next-to-Minimal Supersymmetric Standard Model (NMSSM) could render the scenario `natural', we explore the plausibility of having relatively light neutralinos and charginos (the electroweakinos or the ewinos) in such a scenario with a rather light singlino-like Lightest Supersymmetric Particle (LSP), which is a Dark Matter (DM) candidate, and singlet-dominated scalar excitations. By first confirming the indications in the existing literature that finding simultaneous compliance with results from the Large Hadron Collider (LHC) and those from various DM experiments with such light states is, in general, a difficult ask, we proceed to demonstrate, with the help of a few representative benchmark points, how exactly and to what extent could such a highly motivated `natural' setup with a singlino-like DM candidate still remains plausible., Comment: 29 pages, 3 figures, 2 tables, five references added, version published in JHEP

Presence of nonholomorphic soft SUSY breaking terms is known to be a possibility in the popular setup of the Minimal Supersymmetric Standard Model (MSSM). It has been shown that such a scenario known as NonHolomorphic Supersymmetric Standard Model (NHSSM) could remain `natural' ( i.e., not fine-tuned) even in the presence of a rather heavy higgsino-like LSP. However, it turns out that distinguishing such a scenario from the MSSM is unlikely to be an easy task, in particular at the Large Hadron Collider (LHC). In a first study of such a scenario at colliders (LHC), we explore a possible way that focuses on the sbottom phenomenology. This exploits the usual $\tan\beta$-dependence (enhancement) of the bottom Yukawa coupling but reinforced/altered in the presence of non-vanishing nonholomorphic soft trilinear parameter $A_b^{\prime}$. For a given set of masses of the sbottom(s) and the light electroweakinos (LSP, lighter chargino etc.) which are known from experiments, the difference between the two scenarios could manifest itself via event rate in the 2b-jets + ${\, \not \! \! E_T}$ final state, which could be characteristically different from its MSSM expectation. Impact on the phenomenology of the stops at the LHC is also touched upon., Comment: 32 pages, 17 figures, 1 table, no changes in texts/figures, three references added, version published in JHEP

We study the possibilities and the implications of a spontaneous breakdown of charge in the MSSM and in the $Z_3$-symmetric NMSSM. The breakdown is triggered by the charged states of the Higgs doublets acquiring vacuum expectation values. In the MSSM, it is known that the presence of a charge conserving minimum for the tree-level Higgs potential precludes a deeper (global) charge-breaking minimum. We find that the inclusion of radiative correction to the potential does not alter the situation while a deeper charge-conserving minimum could arise, albeit with no major practical consequences. In the NMSSM scenario, a charge-breaking global minimum, with or without an accompanying charge-conserving deeper minimum, could appear even with the tree-level Higgs potential thanks to the presence of a charge-neutral scalar state which transforms as a singlet under the Standard Model gauge group. Use of the NMSSM Higgs potential that includes both quantum and thermal corrections and the requirement of a viable (stable or long-lived) vacuum that breaks the electroweak symmetry, along with its compatibility with the latest Higgs data, lead to nontrivial constraints on the NMSSM parameter space., Comment: 27 pages, 8 figures, 1 table; matches with published version

We discuss the collider phenomenology of the model of Minimal Universal Extra Dimensions (MUED) at the Large hadron Collider (LHC). We derive analytical results for all relevant strong pair-production processes of two level 1 Kaluza-Klein partners and use them to validate and correct the existing MUED implementation in the fortran version of the PYTHIA event generator. We also develop a new implementation of the model in the C++ version of PYTHIA. We use our implementations in conjunction with the CHECKMATE package to derive the LHC bounds on MUED from a large number of published experimental analyses from Run 1 at the LHC., Comment: 38 pages, 6 figures

We explore the vacua of the $Z_3$-symmetric Next-to-Minimal Supersymmetric Standard Model (NMSSM) and their stability by going beyond the simplistic paradigm that works with a tree-level neutral scalar potential and adheres to some specific flat directions in the field space. Key effects are demonstrated by first studying the profiles of this potential under various circumstances of physical interest via a semi-analytical approach. The results thereof are compared to the ones obtained from a dedicated package like \veva ~which further incorporates the thermal effects to the potential. Regions of the phenomenological NMSSM (pNMSSM) parameter space that render the desired symmetry breaking (DSB) vacuum absolutely stable, long- or short-lived (in relation to the age of the Universe) under quantum/thermal tunneling are delineated. Regions that result in color and charge breaking (CCB) minima are also presented. It is demonstrated that light singlet scalars along with a light LSP (lightest supersymmetric particle) having an appreciable singlino admixture are compatible with a viable DSB vacuum and are much relevant for the collider experiments., Comment: 52 pages, 19 figures, 4 tables; matches with published version

Search for the bottom squarks (sbottoms) at the Large Hadron Collider (LHC) has recently assumed a heightened focus in the hunt for Supersymmetry (SUSY). The popular framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) could conceive a naturally light sbottom which could easily be consistent with available constraints from the experiments at the LHC. Phenomenology of such sbottoms could in principle be as striking as that for a light top squark (stop) thanks to a rather nontrivial neutralino sector (with appreciable mixing among the neutral higgsinos and the singlino) that the scenario gives rise to. Nonetheless, finding such sbottoms might require a moderately large amount of data ($\sim 300$ $\text{fb}^{-1}$) at the 13 TeV run of the LHC. A multi-channel analysis establishing a generic depletion of events in the usual $2b$-$jets$ +$\text{\sout{E}}_T$ final state while registering, in conjunction, characteristically significant rates in various multi-lepton final states accompanied by $b$-$jets$ might point not only to the presence of light sbottom(s) but could also shed crucial light on their compositions and the (singlino) nature of the lightest SUSY particle (LSP)., Comment: 30 pages, 6 figures, 5 tables; matches with published version

We investigate the phenomenology of top squarks at the Large Hadron Collider (LHC) in a supersymmetric model where lepton number is identified with an approximate $U(1)_R$ symmetry in such a way that one of the left chiral sneutrinos can acquire a large vacuum expectation value ($vev$) and can play the role of the down-type Higgs. This $R$-symmetry allows a subset of trilinear $R$-parity violating interactions, which determine the collider phenomenology of this model in a significant way. The gauginos are Dirac particles and gluinos are relatively heavy in this class of models. The model contains a right handed neutrino superfield, which gives a tree level mass to one of the active neutrinos. An order one neutrino Yukawa coupling also helps enhance the Higgs boson mass at the tree level and results in a very light bino-like neutralino ($\widetilde \chi_2^0$) with mass around a few hundred MeV, which is a carrier of missing (transverse) energy (\met). The model can accommodate two rather light top squarks, compatible with the observed mass of the Higgs boson. The lighter top squark (${\widetilde t}_1$) can decay into $t\widetilde\chi_2^0$, and thus the signal would be similar to the signal of top quark pair production at the LHC. In addition, fully visible decays such as ${\widetilde t}_2 \rightarrow b e^+$ can give rise to interesting final states. Such signals at the LHC combined with other features like a heavy gluino could provide a strong evidence for this kind of a model. Our analysis shows that $m_{\widetilde t_1}\lsim 575~(750)$ GeV and $m_{\widetilde t_2}\lsim 1.2~(1.4)$ TeV can be probed with 5$\sigma$ statistical significance at the 13 TeV LHC with 300~(3000) fb$^{-1}$ of integrated luminosity. Finally, we observe that in the presence of super-light carriers of \met, the so-called `stealth' top squark scenario may naturally appear in our model., Comment: Two new figures added, matches with the published version

We study the viability of having two relatively light top squarks (`stops') in the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM). Such light stops render the NMSSM rather `natural'. These are shown to be allowed by the relevant direct searches at the Large Hadron Collider (LHC) and to be compatible with the latest LHC results on the Higgs sector, other low energy electroweak constraints and recent constraints from the dark matter (DM) sector. We propose dedicated searches for such light stops at the LHC within a `simplified' scenario that may have a bino-like or a singlino-like neutralino LSP as the DM candidate and point out various final states carrying the imprint of their collective presence. Under certain circumstances, in such a scenario, presence of two light stops may give rise to final states which are not so typical in their search. Thorough studies at the detector level reveal the status of such a scenario after the 8 TeV run of the LHC and shed light on the prospects of its 13 and 14 TeV runs. In favorable regions of the NMSSM parameter space, with low-lying spectra, signals with significance $\gtrsim 5\sigma$ is possible with a few tens to a few hundreds of $\text{fb}^{-1}$ of integrated luminosity in diverse final states., Comment: 44 pages with 13 figures and 9 tables; matches with published version

We discuss prospects of the $Z'$ search at the LHC in non-minimal Universal Extra Dimensions with tree-level brane-local terms in five dimensions. In this scenario, we find two major differences from the usual $Z'$ physics: (i) two $Z'$ candidates close-by in mass exist; (ii) the effective couplings to the SM fermions could be very large due to drastic overlapping of their profiles along the extra dimension. To evaluate the actual situation precisely, we reconsider the important issues of resonant processes, i.e., treatment of resonant propagators and including interference effects., Comment: 4 pages, 1 figure, 1 table, proceedings of the 2nd Toyama Workshop on "Higgs as a Probe of New Physics 2015" (HPNP2015), 11-15 February 2015

We perform a detailed study of the signal rate of the lightest Higgs boson in the diphoton channel ($\mu_{\gamma \gamma}$), recently analyzed by both the ATLAS and CMS collaborations at the Large Hadron Collider, in the framework of $U(1)_R-$ lepton number model with a right handed neutrino superfield. The corresponding neutrino Yukawa coupling, `$f$', plays a very important role in the phenomenology of this model. A large value of $f\sim\mathcal O(1)$ provides an additional tree level contribution to the lightest Higgs boson mass along with a very light (mass $\sim$ a few hundred MeV) bino like neutralino and a small tree level mass of one of the active neutrinos that is compatible with various experimental results. In the presence of this light neutralino, the invisible decay width of the Higgs boson can become important. We studied this scenario in conjunction with the recent LHC results. The signal rate $\mu_{\gamma\gamma}$ obtained in this scenario is compatible with the recent results from both the ATLAS and the CMS collaborations at 1$\sigma$ level. A small value of `$f$', on the other hand, is compatible with a sterile neutrino acting as a 7 keV dark matter that can explain the observation of a mono-energetic X-ray photon line by the XMM-Newton X-ray observatory. We also study the impact of $\mu_{\gamma\gamma}$ in this case., Comment: 45 pages, Corrected a sign error in the numerical code and included the correct symmetry factor in Eq.(B.8). One figure removed, some modifications in the text, conclusions partially changed. Erratum published in JHEP

We study the physics of Kaluza-Klein (KK) top quarks in the framework of a non-minimal Universal Extra Dimension (nmUED) with an orbifolded (S1/Z2) flat extra spatial dimension in the presence of brane-localized terms (BLTs). In general, BLTs affect the masses and the couplings of the KK excitations in a non-trivial way including those for the KK top quarks. On top of that, BLTs also influence the mixing of the top quark chiral states at each KK level and trigger mixings among excitations from different levels with identical KK parity (even or odd). The latter phenomenon of mixing of KK levels is not present in the popular UED scenario known as the minimal UED (mUED) at the tree level. Of particular interest are the mixings among the KK top quarks from level `0' and level `2' (driven by the mass of the Standard Model (SM) top quark). These open up new production modes in the form of single production of a KK top quark and the possibility of its direct decays to Standard Model (SM) particles leading to rather characteristic signals at the colliders. Experimental constraints and the restrictions they impose on the nmUED parameter space are discussed. The scenario is implemented in MadGraph 5 by including the quark, lepton, the gauge-boson and the Higgs sectors up to the second KK level. A few benchmark scenarios are chosen for preliminary studies of the decay patterns of the KK top quarks and their production rates at the LHC in various different modes. Recast of existing experimental analyzes in scenarios having similar states is found to be not so straightforward for the KK top quarks of the nmUED scenario under consideration., Comment: 47 pages, 16 figures, 5 tables (v1); 47 pages, 16 figures, 6 tables, published version in JHEP with minor modifications, references added (v2)

We work out the strongly interacting sector of a non-minimal Universal Extra Dimension (nmUED) scenario with one flat extra spatial dimension orbifolded on S^1/Z_2 in the presence of brane-localized kinetic and Yukawa terms. On compactification, these terms are known to have significant, nontrivial impact on the masses and the couplings of the Kaluza-Klein (KK) excitations. We study the masses of the level `1' KK gluon and the quarks and find the modified strong interaction vertices involving these particles. The scenario conserves KK parity. Possibility of significant level-mixing among the quarks from different KK-levels is pointed out with particular reference to the top quark sector. Cross sections for various generic final states involving level `1' KK-gluon and KK-quarks from first two generations are estimated at the Large Hadron Collider (LHC) via an implementation of the scenario in MadGraph-5 with the help of FeynRules. The decay branching fractions of both strong and weakly interacting KK excitations are studied to estimate yields in various different final states involving jets, leptons and missing energy. These are used to put some conservative constraints on the nmUED parameter space using the latest LHC data. Nuances of the scenario are elucidated with reference to the minimal Universal Extra Dimension (mUED) and Supersymmetry (SUSY) and their implications for the LHC are discussed., Comment: 45 pages, 11 figures, 3 tables (v1); 39 pages, 8 figures, 4 tables (v2): Version accepted in JHEP. Some sections are added/modified

In the Minimal Supersymmetric extension of the Standard Model (MSSM) squarks from the third generation, i.e., the bottom and the top squarks, have a common set of parameters that determine their masses and couplings. These are in the form of the common soft mass for the left handed squark from the third generation ($m_{\widetilde{Q}_{_{3L}}}$), the supersymmetry conserving Higgsino mass parameter $\mu$ and $\tan\beta$, the ratio of vacuum expectation values of the two Higgs doublets. This leads to an interesting possibility that the systems involving the bottom and the top squarks might get correlated in a non-trivial way even in an unconstrained setup. In this work, phenomenology of the bottom and the top squarks is studied at the Large Hadron Collider which exploits such a possibility with a particular emphasis on bottom squark decaying to top squark and $W$ boson. Possibility of reconstructing multiple $W$ bosons in the final state is identified to be the key in probing the squark mixing angles. Further entanglement of the electroweak gaugino-higgsino sector is also not impossible in scenarios based on phenomenological MSSM while for highly constrained scenarios like minimal supergravity/constrained MSSM such entanglements are trivially forced upon., Comment: 31 pages, 4 figures, 8 tables

We present an implementation of the model of minimal universal extra dimensions (MUED) in CalcHEP/CompHEP. We include all level-1 and level-2 Kaluza-Klein (KK) particles outside the Higgs sector. The mass spectrum is automatically calculated at one loop in terms of the two input parameters in MUED: the radius of the extra dimension and the cut-off scale of the model. We implement both the KK number conserving and the KK number violating interactions of the KK particles. We also account for the proper running of the gauge coupling constants above the electroweak scale. The implementation has been extensively cross-checked against known analytical results in the literature and numerical results from other programs. Our files are publicly available and can be used to perform various automated calculations within the MUED model., Comment: 32 pages, 4 figures, 6 tables, invited contribution for New Journal of Physics Focus Issue on 'Extra Space Dimensions', the model file can be downloaded from http://home.fnal.gov/~kckong/mued/

The Higgs sector of the Universal Extra Dimensions (UED) has a rather involved setup. With one extra space dimension, the main ingredients to the construct are the higher Kaluza-Klein (KK) excitations of the Standard Model Higgs boson and the fifth components of the gauge fields which on compactification appear as scalar degrees of freedom and can mix with the former thus leading to physical KK-Higgs states of the scenario. In this work, we explore in detail the phenomenology of such a Higgs sector of the UED with the Large Hadron Collider (LHC) in focus. We work out relevant decay branching fractions involving the KK-Higgs excitations. Possible production modes of the KK-Higgs bosons are then discussed with an emphasis on their associated production with the third generation KK-quarks and that under the cascade decays of strongly interacting UED excitations which turn out to be the only phenomenologically significant modes. It is pointed out that the collider searches of such Higgs bosons face generic hardship due to soft end-products which result from severe degeneracies in the masses of the involved excitations in the minimal version of the UED (MUED). Generic implications of either observing some or all of the KK-Higgs bosons at the LHC are discussed., Comment: 25 pages, 9 figures and 1 table

We investigate the parameter space of the minimal supersymmetric Standard Model (MSSM) where the gluino and squark masses are much above 1 TeV but the remaining part of the sparticle spectrum is accessible to the Large Hadron Collider at CERN. After pointing out that such a scenario may constitute an important benchmark of gaugino/scalar non-universality, we find that hadronically quiet trileptons are rather useful signals for it. Regions of the parameter space, where the signal is likely to be appreciable, are identified through a detailed scan. The advantage of hadronically quiet trileptons over other types of signals is demonstrated., Comment: Version modified, accepted in Physical Review D

Supersymmetric cascades, involving charginos and neutralinos at various stages, contribute in a significant way to Higgs production at the LHC. We explore the nature of such cascades, completely relaxing the universality of the gaugino masses. It is found that the deviation from the scenario with universal gaugino masses would be reflected in the relative production rates for the lightest Higgs and the charged Higgses, two characteristic particles of an extended Higgs sector., Comment: 14 pages, 22 figures

We study the possible signatures of non-universal scalar masses in supersymmetry at the Large Hadron Collider (LHC). This is done, following our recent study on gaugino non-universality, via a multichannel analysis, based largely on the ratios of event rates for different final states, aimed at minimizing irregularity in the pattern due to extraneous effects and errors. We have studied (a) squark-slepton non-universality, (b) non-universality in sfermion masses of the third family, (c) the effects of $SO(10) D$-terms in supersymmetric Grand Unified Theories. After presenting an elaborate numerical analysis of like- and opposite-sign dileptons, inclusive and hadronically quiet trileptons as well as inclusive jet final states, we point out specific features of the spectrum in each case, which can be differentiated in the above channels from the spectrum for a minimal supergravity scenario with a universal scalar mass at high scale. The event selection criteria, and the situations where the signals are sizable enough for a comparatve study, are also delineated. It is found that, with some exceptions, the trilepton channels are likely to be especially useful for this purpose., Comment: 30 pages, 8 figures

A benchmark CP-violating supersymmetric scenario (known in the literature as `CPX-scenario') is studied in the context of the Large Hadron Collider (LHC). It is shown that the LHC, with low to moderate accumulated luminosity, will be able to probe the existing `hole' in the $m_{h_1}$-$\tan\beta$ plane, which cannot be ruled out by the Large Electron Positron Collider data. This can be done through associated production of Higgs bosons with top quark and top squark pairs leading to the signal \emph{dilepton + $\leq{5}$ jets (including 3 b-jets) + missing ${p_T}$}. Efficient discrimination of such a CP-violating supersymmetric scenario from other contending ones is also possible at the LHC with a moderate volume of data., Comment: LaTeX, 19 pages, 5 figures, added references for section 2, typos corrected

We discuss the signals at the Large Hadron Collider (LHC) for scenarios with non-universal gaugino masses in supersymmetric (SUSY) theories. We perform a multichannel analysis, and consider the ratios of event rates in different channels such as $jets + {E}_T/ $, $same$ - and $opposite$-$sign dileptons$ $+jets+ {E}_T/ $, as well as $single-lepton$ and $trilepton$ final states together with $jets + {E}_T/ $ . Low-energy SUSY spectra corresponding to high-scale gaugino non-universality arising from different breaking schemes of SU(5) as well as SO(10) Grand Unified (GUT) SUSY models are considered, with both degenerate low-energy sfermion masses and those arising from a supergravity scenario. We present the numerical predictions over a wide range of the parameter space using the event generator {\tt Pythia}, specifying the event selection criteria and pointing out regions where signals are likely to be beset with backgrounds. Certain broad features emerge from the study, which may be useful in identifying the signatures of different GUT breaking schemes and distinguishing them from a situation with a universal gaugino mass at high scale. The absolute values of the predicted event rates for different scenarios are presented together with the various event ratios, so that these can also be used whenever necessary., Comment: 54 pages, 18 figures

We analyse hadronically quiet trilepton signatures in the T-parity conserving Littlest Higgs model and in R-parity conserving supersymmetry at the Large Hadron Collider. We identify the regions of the parameter space where such signals can reveal the presence of these new physics models above the Standard Model background and distinguish them from each other, even in a situation when the mass spectrum of the Littlest Higgs model resembles the supersymmetric pattern., Comment: 14 pages, 4 figures, Latex; v2: a few comments and references added, typos corrected, conclusions unchanged, version to be published in Physics Letters B

If a signal for physics beyond the Standard Model is observed at the Tevatron collider or LHC, we will be eager to interpret it. Because only certain observables can be studied at a hadron collider, it will be difficult or impossible to measure masses and spins that could easily establish what physics was being seen. Nevertheless, different underlying physics implies different signatures. We examine the main signatures for supersymmetry, with some emphasis on recognizing supersymmetry in parts of parameter space where generic signatures are reduced or absent. We also consider how to distinguish supersymmetry from alternatives that most closely resemble it, such as Universal Extra Dimensions (UED). Using the robust connection between spins and production cross section, we think it will not be difficult to distinguish UED from supersymmetry. We expect that by considering patterns of signatures it is very likely that it will not be difficult to find a compelling interpretation of any signal of new physics., Comment: 31 pages, 11 figures, 3 tables

We contrast the experimental signatures of low energy supersymmetry and the model of Universal Extra Dimensions and discuss various methods for their discrimination at hadron colliders. We study the discovery reach of the Tevatron and the LHC for level 2 Kaluza-Klein modes, which would indicate the presence of extra dimensions. We find that with 100 ${\rm fb}^{-1}$ of data the LHC will be able to discover the $\gamma_2$ and $Z_2$ KK modes as separate resonances if their masses are below 2 TeV. We also investigate the possibility to differentiate the spins of the superpartners and KK modes by means of the asymmetry method of Barr., Comment: 34 pages, 21 figures

Quark-lepton unification suggests Cabibbo-sized effects in lepton mixings, which we call Cabibbo haze. We give simple examples and explore possible Wolfenstein-like parametrizations of the MNSP matrix which incorporate leptonic Cabibbo shifts. We find that the size of the CHOOZ angle is not always correlated with the observability of CP violation., Comment: 10 pages

Universal extra dimensions and supersymmetry have rather similar experimental signatures at hadron colliders. The proper interpretation of an LHC discovery in either case may therefore require further data from a lepton collider. In this paper we identify methods for discriminating between the two scenarios at the linear collider. We study the processes of Kaluza-Klein muon pair production in universal extra dimensions in parallel to smuon pair production in supersymmetry, accounting for the effects of detector resolution, beam-beam interactions and accelerator induced backgrounds. We find that the angular distributions of the final state muons, the energy spectrum of the radiative return photon and the total cross-section measurement are powerful discriminators between the two models. Accurate determination of the particle masses can be obtained both by a study of the momentum spectrum of the final state leptons and by a scan of the particle pair production thresholds. We also calculate the production rates of various Kaluza-Klein particles and discuss the associated signatures., Comment: 20 pages, 13 figures, typeset in JHEP style, uses axodraw. Added new section 5. Version to appear in JHEP

We introduce a new parametrization of the MNS lepton mixing matrix which separates the hierarchical Grand Unified relations among quarks and leptons. We argue that one large angle stems from the charged leptons, the other from the seesaw structure of the neutral lepton mass matrix. We show how two large mixing angles can arise naturally provided there are special requirements on the Dirac ($\Delta I_{\rm w}=1/2$) and Majorana ($\Delta I_{\rm w}=0$) masses. One possibility is a correlated hierarchy between them, the other is that the $\Delta I_{\rm w}=0$ Majorana mass has a specific texture; it is Dirac-like for two of the three families., Comment: 15 pages, no fig, some refs. added

In the context of the Minimal Supersymmetric extension of the Standard Model, we study the production of Higgs bosons at the Large Hadron Collider via cascade decays of scalar quarks and gluinos. We focus on the cascades involving heavier charginos and neutralinos, which decay into the neutral $h,A,H$ and charged $H^\pm$ bosons and lighter charginos and neutralinos, but we will also discuss direct decays of third--generation squarks into their lighter partners and Higgs bosons as well as top quark decays into $H^\pm$ bosons. We show that the production rates of relatively light Higgs bosons, $M_\Phi \lsim 250$ GeV, via these mechanisms can be rather large in some areas of the parameter space. Performing a fast detector simulation analysis that takes into account the signals and the various backgrounds, we show that the detection of the neutral Higgs bosons through their decays into $b\bar{b}$ pairs, and of the charged Higgs particles through the $\tau^\pm \nu$ signature, is possible at the LHC., Comment: 44 pages, latex, 17 figures

Supersymmetry may resolve the disagreement between the precision electroweak data and the direct limit on the higgs mass, if there are light sneutrinos in the mass range 55 GeV $ < m_{\snu} < $ 80 GeV. Such sneutrinos should decay invisibly with 100% branching ratio and contribute to the $\gamma$ + missing energy signal, investigated by all the LEP groups. It is shown that while the data accumulated by a single group may not be adequate to reveal such sneutrinos, a combined analysis of the data collected by all four groups will be sensitive to $m_{\snu}$ in the above range. If no signal is found a lower bound on $m_{\snu}$ stronger than that obtained from the $Z$-pole data may emerge., Comment: 12 pages, LaTeX, 1 postscript figure included, uses epsfig.sty Minor revisions in the discussion of future prospects, 1 ref added

We analyze the associated production at future high--energy $e^+e^-$ colliders, of first generation sleptons with neutralinos and charginos in the modes $e^+ e^-$ and $e \gamma$, in the framework of the Minimal Supersymmetric extension of the Standard Model. We show that the production rates, in particular for associated production of right--handed selectrons and the lightest neutralino which in general is the first accessible kinematically, can be much larger than the corresponding ones for second and third generation scalar leptons and for scalar quarks. With the high--luminosities expected at these colliders, the detection of first generation sleptons with masses significantly above the kinematical two--body threshold, $\sqrt{s}= 2m_{\tilde{l}}$, is thus possible in favourable regions of the parameter space., Comment: 24 pages, latex, axodraw.sty, 6 figures

In the context of the Minimal Supersymmetric extension of the Standard Model, we analyze the production at future high-energy $e^+e^-$ colliders of second and third generation scalar leptons as well as scalar quarks in association with neutralinos and charginos, $e^+e^-\to f\tilde{f}\chi$. In the case of third generation squarks, we also discuss the associated production with gluinos. We show that the cross sections for some of these three-body final state processes could be significant enough to allow for the detection of scalar fermions with masses above the kinematical two--body threshold, $\sqrt{s}= 2m_{\tilde{f}}$. We then discuss, taking as a reference example the case of scalar muons, the production cross sections in various approximations and make a comparison with the full four-body production process, $e^+e^- \to f\bar{f} \chi \chi$, in particular around the two-sfermion threshold., Comment: 32 pages, latex, axodraw.sty, 10 figures

We analyze the cascade decays of the scalar quarks and gluinos of the Minimal Supersymmetric extension of the Standard Model, which are abundantly produced at the Large Hadron Collider, into heavier charginos and neutralinos which then decay into the lighter ones and charged Higgs particles, and show that they can have substantial branching fractions. The production rates of these Higgs bosons can be much larger than those from the direct production mechanisms, in particular for intermediate values of the parameter $\tan \beta$, and could therefore allow for the detection of these particles. We also discuss charged Higgs boson production from direct two-body top and bottom squark decays as well as from two- and three-body gluino decays., Comment: 30 pages with 10 figures, latex. Uses axodraw.sty and epsfig.sty

We discuss the production at $e^+e^-$ colliders of Higgs bosons in association with both the scalar leptons and the lightest neutralinos in the Minimal Supersymmetric extension of the Standard Model. While the rates for associated Higgs production with neutralinos and first/second generation sleptons are rather tiny, the cross section for the production of the lightest Higgs boson $h$ with scalar $\tau$ lepton pairs can reach the femtobarn level at c.m. energies at and above 500 GeV in favorable regions of the parameter space, making this process potentially detectable at a high-luminosity $\ee$ collider, in particular in the $\gamma \gamma$ option. This would provide a determination of the $h \tilde{\tau} \tilde{\tau}$ coupling and opens up the possibility of measuring the parameter $\tan \beta$., Comment: 10 pages, latex, axodraw.sty, 2 psfigures

Thanks to the focus point phenomenon, it is quite {\it natural} for the minimal SUGRA model to have a large soft scalar mass m_0 > 1 TeV. A distinctive feature of this model is an inverted hierarchy, where the lighter stop has a significantly smaller mass than the other squarks and sleptons. Consequently, the gluino is predicted to decay dominantly via stop exchange into a channel containing 2b and 2W along with the LSP. We exploit this feature to construct a robust signature for this model at the LHC in leptonic channels with 3-4 b-tags and a large missing-E_T., Comment: Small clarifications added. Final version to appear in Phys. Lett. B

In an R-parity nonconserving supersymmetric theory, the lighter stop can dominantly decay into $b\mu$ and $b\tau$ if R-parity breaking has to explain the neutrino mass and mixing pattern suggested by the data on atmospheric muon neutrinos. This should give rise to $dilepton+dijet$ and $single-lepton+jets$, signals resembling those of the top quark at the Fermilab Tevatron. One can thus constrain the stop parameter space using the current top search data, and similarly look for the first signals of supersymmetry at the upgraded runs of the Tevatron., Comment: 13 pages, RevTeX, 2 PS figures, uses epsfig.sty, few comments and references added, version to appear in Phys. Rev. Lett

We show that an R-parity violating supersymmetric scenario which can account for the atmospheric nu(mu) deficit has testable signals at the Fermilab Tevatron with upgraded energy and luminosity. The explanation of neutrino masses and maximal nu(mu)-nu(tau) oscillation in terms of bilinear R-violating terms in the superpotential associates comparable numbers of muons and tau's resulting from decays of the lightest neutralino. We show that this should lead to like-sign dimuons and ditaus with substantial rates, in a form that separates them from standard model backgrounds and other signals of supersymmetry. One here also has the possibility of completely reconstructing the lightest neutralino., Comment: 10 pages, 4 figures (ps files included). Matches published version

We study signals for the production of superparticles at the Tevatron in supergravity scenarios based on the Grand Unified group SO(10). The breaking of this group introduces extra contributions to the masses of all scalars, described by a single new parameter. We find that varying this parameter can considerably change the size of various expected signals studied in the literature, with different numbers of jets and/or charged leptons in the final state. The ratios of these signal can thus serve as a diagnostic to detect or constrain deviations from the much--studied scenario where all scalar masses are universal at the GUT scale. Moreover, under favorable circumstances some of these signals, and/or new signals involving hard $b-$jets, should be observable at the next run of the Tevatron collider even if the average scalar mass lies well above the gluino mass., Comment: 17 pages, LaTeX including 3 postscript figures, uses equation.sty

The constraints on an R-parity violating supersymmetric theory arising from the recent SuperKamiokande results on atmospheric neutrinos are studied, with special reference to a scenario with bilinear R-parity violating terms. Considering both the fermionic and scalar sectors, we find that a large area of the parameter space is allowed, in terms of both the lepton-number violating entries in the superpotential and the soft R-violating terms in the scalar potential, and that no fine-tuning is required. However, the need to avoid flavour changing neutral currents puts additional restrictions on the theory, requiring either the R-violating terms in the superpotential to be smaller than the R-conserving ones, or a hierarchy in the R-violating parameters for different lepton flavours in the superpotential., Comment: 18 pages, LaTex including postscript figures

In minimal supergravity based supersymmetry models the charged sleptons as well as the sneutrinos may be lighter than the squarks. In such light slepton scenario the search for lighter stop squark has been investigated in the dilepton + missing $p_T(\missingpt)$ +jets ($\ge 1$) channel at Tevatron. In this scenario semileptonic decay of lighter stop squark has been considered via off shell and on shell charginos. In the latter case the chargino undergoes pure leptonic 2-body decay. We observe that for some favourable region of the MSSM parameter space one can probe lighter stop squark mass upto 140 GeV with few events in the present data set for which the luminosity is 110 pb$^{-1}$. At the MI upgrade one is likely to end up with more events., Comment: 20 pages, LaTeX, including 3 postscript figures, to appear in Int. Journal of Mod. Physics A

We identify several mass patterns, within the framework of N=1 SUGRA with nonuniversal soft breaking masses for the sfermions, which may significantly alter SUSY signals and the current squark-gluino mass limits from the Tevatron. These effects are illustrated in a SO(10) SUSY GUT with an intermediate mass scale, but the conclusions are also valid in SUSY SO(10) models with grand deserts., Comment: 17 pages, two ps figures, LaTeX format

We show that the process $e^+e^- \to \gamma+$ missing energy, arising from the pair production of neutralinos, can probe the $\gamma-\tilde\gamma- \gravitino$ as well as the $Z-\tilde Z-\gravitino$ couplings in Gauge Mediated Supersymmetry Breaking models. This enables one to study the mutual relationship of the Goldstino couplings of the different gauginos, a feature whose testability has not been emphasized so far. The Standard Model backgrounds get suppresed with the use of a right polarized electron beam. The energy and angular distribution of the emitted photon can distinguish such models from the minimal supersymmetric theory and its variants., Comment: Revised version to be published in Physics Letters B. Some minor changes were made

Currently popular search strategies for supersymmetric particles may be significantly affected due to relatively light sneutrinos which decay dominantly into invisible channels. In certain cases the second lightest neutralino may also decay invisibly leading to two extra carriers of missing energy (in addition to the lightest supersymmetric particle (LSP)) -- the virtual LSPs (VLSPs). It is shown that if the sneutrino masses happen to be in the small but experimentally allowed range ~ 45 - 55 GeV, these particles together with neutralino pairs may contribute significantly to the missing energy in the process e+ e- ---> \gamma + missing energy at LEP-2 energies as an enhancement over the Standard Model or the conventional MSSM predictions. It is further shown that a much larger region of the parameter space can be scanned at a high luminosity e+ e- collider at 500 GeV like the proposed NLC machine. Moreover this process can play a complementary role to direct chargino searches at LEP-2 and NLC which may fail due to a near mass degeneracy of the chargino and the sneutrino. Formulae for the cross sections taking into account full mixings of the charginos and the neutralinos are derived. The signal remains observable even in the context of more restricted models based on N=1 SUGRA with common scalar and gaugino masses. The effect of soft photon brehmsstrahlung on the signal is also discussed briefly., Comment: 51 pages, LaTeX plus 13 postscript figures included using epsfig in uuencoded and compressed form, minor comments added

In the minimal supersymmetric extension of the Standard Model (MSSM) with $R$-parity conservation the possibility that the sneutrino and the second lightest neutralino decay dominantly into invisible channels and, in addition to the lightest neutralino, carry missing energy, is still open --- both theoretically and experimentally. It is shown that for a large region of the parameter space allowed by {\rm LEP-I} data, these particles can contribute significantly to the process $e^+ e^- \longrightarrow \gamma$ + {\rm nothing}. This signal, if it exists, can be easily detected at {\rm LEP-II} as an enhancement over the Standard Model or the conventional MSSM predictions., Comment: 11 pages,latex,4 figs(available from the authors on request)